Multijunction optoelectronic devices including device interlayers

Abstract

The present invention provides a photoelectric conversion device comprising: a) a first photoactive region comprising a layer of a first photoactive material; b) a second photoactive region comprising a layer of a second photoactive material; and c) a charge recombination layer disposed between the first photoactive region and the second photoactive region, wherein the charge recombination layer comprises a charge recombination layer material, wherein one of the first and second photoactive materials comprises at least one A / M / X material; and wherein the other of the first and second photoactive materials comprises at least one A / M / X material or a compound that is a photoactive semiconductor other than an A / M / X material; and wherein each A / M / X material has a structure represented by Formula (I)[A] a [M] b [X] c wherein: [A] comprises one or more A cations; [M] comprises one or more M cations that are metal or semi-metal cations; [X] comprises one or more X anions; a is a number from 1 to 6; b is a number from 1 to 6; and c is a number from 1 to 18; and wherein the charge recombination layer material has a refractive index, n(λ), of at least 2 at a wavelength, λ, where λ is a wavelength between 500 nm and 1200 nm.

Description

[Technical field]

[0001] FIELD OF THEINVENTION The present invention provides a multijunction device that includes a first photoactive region including a layer of a first photoactive material, a second photoactive region including a layer of a second photoactive material, and a charge recombination layer disposed between the first and second photoactive regions. [Background technology]

[0002] 2. Background of the Invention To provide a perovskite solar cell that reaches its thermodynamically limited efficiency, the device stack must be simultaneously optimized electronically and optically. The open circuit voltage (V oc ) and fill factor losses, the short circuit current density (J sc Optical optimization to increase the efficiency (at 1000 nm) has been somewhat neglected. Single-junction cells can usually be optimized by brute force optimization of layer thicknesses. However, due to the large number of layers in multijunction devices, complex optical modeling is required to maximize the optical absorption and therefore the efficiency [Horantner et al., ACS Energy Letters 2, no. 10 (2017): 2506-13].

[0003] Multijunction devices consist of two or more absorbers of different bandgaps, stacked so that each absorber absorbs photons from a different part of the spectrum. This helps to reduce the energy loss as carrier thermalization and increases the power conversion efficiency (PCE) from absorbed sunlight to electricity. The simplest multijunction device is the tandem device, which has two absorbers as shown in Figure 1. For a monolithic tandem cell, where all the subcells are processed on top of each other and power is extracted through two terminals, the two subcells are electrically connected in series by a recombination layer.

[0004] As an alternative to the two-terminal monolithic approach for tandem solar cells, it is possible to fabricate two solar cells separately on separate substrates and subsequently stack them together. This is often referred to as a four-terminal stacked tandem cell. However, this four-terminal stacked approach has several disadvantages. One disadvantage is the requirement of at least three highly transparent and highly conductive electrodes, which increases costs and reduces the transmission of light from the top cell to the bottom cell. A further disadvantage of the four-terminal stacked approach is the need to fabricate two completely separate modules and have two completely separate electronic circuits for the two subcells, further increasing costs. In contrast, the two-terminal monolithic approach only requires the deposition of additional layers, and all costs associated with turning the deposited thin films into a module remain similar to a single-junction module.

[0005] For perovskite solar cells based on metal halide perovskites, there have been two successful strategies that have delivered functional monolithic two-terminal tandem cells. One strategy is to use physical vapor deposition of a perovskite absorber layer in parallel with physical vapor deposition of charge extraction and charge recombination layers. By these means, very thin charge transport and charge recombination layers can be processed (thicknesses of ∼5–20 nm). Because these thicknesses are much smaller than a quarter of the wavelength of sunlight spanning the visible to near-infrared region of the spectrum, optical interference and reflection within and between these layers are not as much of a problem. An additional advantage of physical vapor deposition is that dissolution of the underlying layers due to solvent interactions does not need to be considered. However, to date, the highest quality perovskite absorbers have been processed by solution processing, which is easier to do than vapor deposition. One issue with solution processing is that the solvents used to deposit layers on the device stack can decompose previously deposited layers, leading to degradation of device performance. Solvents such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), γ-butyrolactone and dimethylacetamide (DMA) are often used to deposit perovskite precursors to form the photoactive layer. However, these solvents have a tendency to remove pre-existing organic layers during device fabrication. Also, if a perovskite layer is already present in the device stack, these solvents may decompose the perovskite layer unless steps are taken to prevent solvent penetration into the device stack. One option to inhibit solvent penetration is to use a recombination layer as a physical barrier, which prevents the solvent used to deposit the second cell from dissolving the layers that form the first cell underneath. Thus, there is a need to develop a recombination layer that is also substantial enough to prevent the solvent from damaging the underlying layers during device fabrication, with minimal optical interference and reflection.

[0006] A second approach to making functional tandem cells that allows the use of solution-processed perovskite layers employs an intermediate dense metal oxide layer of indium tin oxide (ITO) as the recombination layer. This ITO intermediate layer has two functions: first, it acts as a physical barrier to the solvent used to process the second perovskite absorber layer, allowing the use of multiple solution-processed layers. Second, it acts as a semi-transparent charge recombination layer, allowing the monolithic series interconnection of the two subcells. However, these layers produce significant reflection losses from the infrared region of the spectrum (above 750 nm), and therefore the current densities resulting from the lower band gap cells in such devices are much lower than desired. Thus, there is a need to provide a recombination layer that can better prevent reflection losses in the infrared region of the spectrum and maximize the performance of both the top and bottom cells in multijunction devices.

[0007] Horantner et al. propose maximizing the current density in perovskite tandem cells by completely removing the ITO layer and having extremely thin electron and hole charge extraction layers. In practice, however, this would be impractical, since there would be no suitable solvent barrier for the subsequently processed perovskite absorber layers. As discussed above, if there is no (or very thin) barrier between the perovskite absorber layers, the solvent used to deposit the second perovskite layer could dissolve the underlying perovskite layer and possibly any other organic n-type or p-type layers present. This is impractical for device fabrication.

[0008] In semiconductors, the refractive index n is equal to the band gap E g It is well known empirically that increases as decreases ("Moss's law") [Herve and LKJ Vandamme, Infrared Physics and Technology 35, no. 4 (1994): 609-15]. n 4 E g = constant Thus, in multijunction cells, light is expected to encounter a sharp change in refractive index as it travels successfully through absorbers of varying band gaps. This index mismatch causes light to be reflected out of the stack, resulting in a reduction in solar radiation absorbed in the rear subcell and a subsequent reduction in current density. All absorbers in the stack, except for the widest band gap, are subject to this reflection loss. Reflection is also wavelength dependent. The major reflection loss in all perovskite tandem cells employing an indium tin oxide (ITO) recombination layer is at the top cell-ITO-bottom cell interface. Reflection varies between slight and severe depending on the phase difference between the waves reflected from the top and bottom interfaces of the recombination layer. For wavelengths where interference is destructive, very little reflection is seen. Severe reflection is seen at wavelengths where interference is constructive. The same constructive interference is identified as the cause behind the large dip typically seen in the external quantum effect (EQE) spectra of the tandem lower cell [Giles E. et al., Eperon, Science 354, no. 6314 (2016): 861-65]. The presence of the dip indicates that it is a purely optical phenomenon, even in optically produced EQE spectra in the literature [Maximilian T. Horantner et al., ACS Energy letters 2, no. 10 (2017): 2506-13]. The elimination of this reflection loss is highly desirable in the quest for optically optimized perovskite multijunction devices.

[0009] All perovskite multijunction devices suffer from this loss, but the loss is particularly large in tandem cells, where the two absorber bandgaps are most widely spaced compared to other multijunction cells. All perovskite tandem cells exhibit this large mismatch in refractive index at the top absorber-ITO and ITO-bottom absorber interfaces:

[0010] Therefore, there is a need to optimize the optical properties of multijunction devices so that higher short circuit current densities can be achieved.

[0011] Eperon et al. [Giles E. et al. Eperon, Science 354, no. 6314 (2016): 861-65] disclose tandem perovskite-perovskite photovoltaics using a layer of sputter-coated ITO as a recombination layer. As mentioned above, such layers act as a barrier to solvent attack on the underlying perovskite layer during device fabrication, but they also cause significant losses due to reflection within the device.

[0012] Horantner et al. [Maximilian T. Horantner et al., ACS Energy letters 2, no. 10 (2017): 2506-13] discuss modeling for optimizing the band gap and thickness of layers in tandem devices. Horantner et al. suggest that the best improvement to device efficiency could be obtained by completely removing the ITO recombination layer. As mentioned above, this is not practical for solution-processed devices, where the recombination layer acts as a barrier to protect the underlying layers when the second cell is fabricated.

[0013] Mazarella et al. [Mazarella. L. et al. Optics Express, Vol. 26, No. 10 (2018), A487] is concerned with optical simulations for perovskite / silicon heterojunction tandem solar cells. Jager et al. [Jager. K. et al., Optics Express, Vol. 25, No. 12 (2017), A473] is concerned with optimizing layer thicknesses in silicon / perovskite tandem solar cells. This document also focuses on the use of an ITO recombination layer.

[0014] Thus, a need exists for a recombination layer that has optimal optical properties, can be easily deposited by conventional means such as sputter coating or solution processing, and can act as a barrier layer to prevent damage to the underlying structure due to the deposition of the further (solution-processed) layers, as well as the requisite electrical properties to enable charge recombination. Summary of the Invention [Means for solving the problem]

[0015] Summary of the Invention Now, the inventors have established a new solution to this problem: they realised that replacing the ITO interlayer with a semi-transparent material with an optimised refractive index (preferably intermediate between those of the upper and lower perovskite absorber layers) could satisfy both requirements for a dense material of suitable thickness for solvent blocking, whilst facilitating the forward transfer of light to the rear cell (minimising reflection losses).

[0016] Table 1 shows the refractive index change, or refractive index mismatch, for a perovskite (perov) subcell at different interfaces with other perovskite subcells, silicon (Si) subcells and copper indium gallium sulfide (selenide) (CIGS) subcells in a solar cell. For the tandem cell type, the brackets give the band gap of the absorber material in the different subcells. Next to the refractive index mismatch, the value in brackets is the wavelength of light for which this mismatch is estimated.

[0017] [Table 1]

[0018] In devices using an ITO interlayer, the mismatch in refractive index between the ITO layer and the perovskite absorber layer, and the fact that ITO must have a certain thickness to perform its role as a solvent blocking layer, results in significant optical interference within the device stack and significant reflection losses from the infrared region of the spectrum. As a result, the current density generated from the lower bandgap cell in such devices is much lower than desired. By providing the device with an interlayer with an optimized refractive index, this problem is avoided and the power conversion efficiency (PCE) can be increased, since the access of (generally longer wavelength) light to the lower cell (usually the lower bandgap cell) is improved.

[0019] Unexpectedly, the inventors also demonstrate that index-matched devices are less sensitive to changes in the angle of incidence, thus making such devices better suited for real-world applications where the angle of incidence varies with time of day, season, weather (cloud cover or direct sunlight), humidity, dust, and location. Such cells are therefore well suited for use in locations where diffuse light (as opposed to direct sunlight) may dominate, for example in countries where overcast skies are commonplace.

[0020] A further unexpected discovery with respect to the devices of the present invention is that the performance of such devices is significantly less sensitive to expected random variations in layer thickness during fabrication as compared to cells employing known ITO interlayers. Thus, the present invention overcomes many of the problems noted with existing multijunction devices.

[0021] Thus, the present invention provides a) a first photoactive region comprising a layer of a first photoactive material; b) a second photoactive region comprising a layer of a second photoactive material; and c) a charge recombination layer disposed between the first photoactive region and the second photoactive region, where the charge recombination layer comprises a charge recombination layer material; wherein one of the first and second photoactive materials comprises at least one A / M / X material; and wherein the other of the first and second photoactive materials comprises at least one A / M / X material or a compound that is a photoactive semiconductor other than an A / M / X material; and wherein each A / M / X material is a crystalline compound of formula (I), [A] a [M] b [X] c (I) wherein: [A] comprises one or more A cations; [M] comprises one or more M cations which are metal or semi-metal cations; [X] comprises one or more X anions; a is a number from 1 to 6; b is a number from 1 to 6; and c is a number from 1 to 18; and wherein the charge recombination layer material has a refractive index, n(λ), of at least 2 at a wavelength λ, where λ is a wavelength between 500 nm and 1200 nm. A multijunction device is provided. [Brief description of the drawings]

[0022] [Figure 1] Figure 1 shows a schematic (top) and a cross-sectional SEM image (bottom) of a perovskite-perovskite tandem solar cell. (Drawings taken from [Giles E. et al. Eperon, Science 354, no. 6314 (2016): 861-65].) [Figure 2A] FIG. 2A shows how reflections from the recombination layer occur from the upper cell, recombination layer interface (phase angle φ1) and the recombination layer, lower cell interface (phase angle φ2). [Figure 2B] FIG. 2B shows the refractive index of 1.8 eV gap and 1.2 eV band gap perovskite absorber layers along with the refractive index of typical transparent conductive oxides fluorine doped tin oxide (FTO) and indium tin oxide (ITO).

[0023]

number

[0024] where n1(λ0) and n2(λ0) are the refractive indices of the upper and lower perovskite layers at λ0 = 850 nm. Also shown is a dashed line indicating the approximate ideal refractive index to minimize reflection losses between the two perovskite layers, calculated as [Figure 3A] FIG. 3A shows how the external quantum effect (EQE) is affected by constructively interfering reflections (tITO=83 nm). [Figure 3B] FIG. 3B shows how the EQE is affected by a destructively interfering reflection (tITO=173 nm). [Figure 3C] FIG. 3C shows how the EQE is affected in the absence of a recombination layer. [Figure 3D] FIG. 3D shows the variation of the bottom cell current with the recombination layer thickness. [Figure 4A] FIG. 4A shows the EQE results for the optimized perovskite-perovskite tandem with an ITO recombination layer (203 nm) yielding a PCE of 28.8%. [Figure 4B] FIG. 4B shows the EQE results for the optimized perovskite-perovskite tandem with n=2.45 interlayers resulting in a PCE of 29.38%. [Figure 4C] FIG. 4C shows the current density in the bottom cell as a function of the recombination layer thickness and refractive index. [Figure 4D] FIG. 4D shows the PCE as a function of recombination layer thickness for ITO and a material with a refractive index of 2.2. [Figure 5A] FIG. 5A shows the PCE as a function of Nb:TiO2 fraction in ITO / Nb:TiO2 mixed interlayers. [Figure 5B] FIG. 5B shows the PCE as a function of the recombination layer thickness for various ITO / Nb:TiO2 mixture ratios. [Figure 6] Figure 6 shows how the Nb:TiO2 rate-matched cell is less sensitive to changes in incidence angle. At 50° incidence, the Nb:TiO2 interlayer gives a 1.1% (absolute) efficiency gain over the ITO interlayer. [Figure 7] FIG. 7 shows the PCE distribution with 5% standard deviation in layer thickness during the fabrication of index-matched cells (TiO 2 interlayer) and ITO interlayer cells. [Figure 8] Figure 8 is a schematic diagram of a potential device stack that includes an optical spacer layer, in which the recombination layer is Nb-doped TiO2 (Nb:TiO2). [Figure 9] FIG. 9 shows the optical constants of the sputtered Nb-doped (4%) TiO2 thin film (80 nm) of Example 2 measured using ellipsometry. [Figure 10] FIG. 10 shows the transmittance and reflectance spectra of Nb-doped (4%) TiO 2 thin film (80 nm) sputtered on glass in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Detailed Description of the Invention definition The term "crystalline" as used herein refers to a crystalline compound, which is a compound that has an extended 3D crystal structure. A crystalline compound is typically in the form of crystals, or in the case of polycrystalline compounds, in the form of microcrystals (i.e., multiple crystals with particle sizes of 1 μm or less). The crystals often form layers together. The crystals of a crystalline material can be of any size. When the crystals have one or more dimensions ranging from 1 nm to 1000 nm, they can be described as nanocrystals.

[0026] The terms "organic compound" and "organic solvent" as used herein have their typical meanings in the art and would be readily understood by one of ordinary skill in the art.

[0027] As used herein, the term "crystalline A / M / X material" refers to a material having a crystalline structure that includes one or more A ions, one or more M ions, and one or more X ions. The A and M ions are cations. The X ions are anions. A / M / X materials typically do not include any additional types of ions.

[0028] The term "perovskite" as used herein refers to a material having a three-dimensional crystal structure related to that of CaTiO3 or a material containing a layer of a material having a structure related to that of CaTiO3. The structure of CaTiO3 can be represented by the formula ABX3, where A and B are cations of different sizes and X is an anion. In the unit cell, the A cations are at (0,0,0), the B cations are at (1 / 2, 1 / 2, 1 / 2), and the X anions are at (1 / 2, 1 / 2, 0). The A cations are usually larger than the B cations. Those skilled in the art will understand that when A, B, and X are varied, the different ion sizes can distort the structure of the perovskite material from that adopted by CaTiO3 to a distorted structure with less symmetry. The symmetry is also lower when the material contains a layer with a structure related to that of CaTiO3. Materials containing layers of perovskite materials are well known. For example, the structure of the material adopting the K2NiF4-type structure includes a layer of perovskite material. Those skilled in the art understand that perovskite materials can be represented by the formula [A][B][X]3, where [A] is at least one cation, [B] is at least one cation, and [X] is at least one anion. When the perovskite contains more than one A cation, the different A cations can be distributed across the A sites in an ordered or disordered manner. When the perovskite contains more than one B cation, the different B cations can be distributed across the B sites in an ordered or disordered manner. When the perovskite contains more than one X anion, the different X anions can be distributed across the X sites in an ordered or disordered manner. The symmetry of perovskites containing more than one A cation, more than one B cation, or more than one X cation is lower than that of CaTiO3. For layered perovskites, the stoichiometry can vary between the A, B and X ions. As an example, an [A]2[B][X]4 structure can be adopted when the A cation has an ionic radius that is too large to fit within the 3D perovskite structure. The term "perovskite" also includes A / M / X materials that adopt the Rdolphin-Popper phase.The Rdolphin–Popper phase refers to perovskites that have a mixture of layered and 3D components. Such perovskites have the crystal structure A. n-1 A'2M n X 3n+1 where A and A' are different cations and n is an integer from 1 to 8, or from 2 to 6. The term "mixed 2D and 3D" perovskites may be used, for example, AMX3 and A n-1 A'2M n X 3n+1 It is used to refer to a perovskite film in which both regions or domains of the perovskite phase are present.

[0029] As used herein, the term "metal halide perovskite" refers to a perovskite whose formula includes at least one metal cation and at least one halide anion.

[0030] As used herein, the term "mixed halide perovskite" refers to a perovskite or mixed perovskite that contains at least two types of halide anions.

[0031] As used herein, the term "mixed cation perovskite" refers to a perovskite or mixed perovskite that contains at least two types of A cations.

[0032] As used herein, the term "organic-inorganic metal halide perovskite" refers to a metal halide perovskite whose formula includes at least one organic cation.

[0033] As used herein, the term "monocation" refers to any cation having a single positive charge, i.e., a cation of formula A + As used herein, the term "dication" refers to any cation having two positive charges, i.e., a cation of the formula A 2+As used herein, the term "trication" refers to any cation having three positive charges, i.e., a cation of the formula A 3+ As used herein, the term "tetracation" refers to any cation having four positive charges, i.e., a cation of the formula A 4+ where A is any moiety, for example a metal atom, refers to a cation of.

[0034] As used herein, the term "alkyl" refers to a straight or branched chain saturated hydrocarbon group. An alkyl group is any of the C 1-20 Alkyl group, C 1-14 Alkyl group, C 1-10 Alkyl group, C 1-6 Alkyl group or C 1-4 It may be an alkyl group. 1-10 Examples of alkyl groups are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. 1-6 Examples of alkyl groups are methyl, ethyl, propyl, butyl, pentyl or hexyl. 1-4 Examples of alkyl groups are methyl, ethyl, i-propyl, n-propyl, t-butyl, s-butyl or n-butyl. When the term "alkyl" is used anywhere in this specification without a prefix specifying the number of carbons, it has 1 to 6 carbons (and this also applies to any other organic groups referenced herein).

[0035] As used herein, the term "cycloalkyl" refers to a saturated or partially unsaturated cyclic hydrocarbon group. A cycloalkyl group is a C 3-10 Cycloalkyl groups, C 3-8 Cycloalkyl group or C 3-6 It may be a cycloalkyl group. 3-8 Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexenyl, cyclohexy-1,3-dienyl, cycloheptyl, and cyclooctyl. 3-6Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

[0036] As used herein, the term "alkenyl" refers to a straight or branched chain hydrocarbon group containing one or more double bonds. An alkenyl group is a C 2-20 Alkenyl group, C 2-14 Alkenyl group, C 2-10 Alkenyl group, C 2-6 Alkenyl group or C 2-4 It may be an alkenyl group. 2-10 Examples of alkenyl groups are ethenyl (vinyl), propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl or decenyl. 2-6 Examples of alkenyl groups are ethenyl, propenyl, butenyl, pentenyl or hexenyl. 2-4 Examples of alkenyl groups are ethenyl, i-propenyl, n-propenyl, s-butenyl or n-butenyl. Alkenyl groups typically contain one or two double bonds.

[0037] The term "aryl" as used herein refers to a monocyclic, bicyclic or polycyclic aromatic ring containing 6 to 14 carbon atoms, typically 6 to 10 carbon atoms, in the ring portion. Examples include phenyl, naphthyl, indenyl, indanyl, anthracenyl and pyrenyl groups. The term "aryl group" as used herein includes heteroaryl groups.

[0038] The term "heteroaryl" as used herein refers to a monocyclic or bicyclic heteroaromatic ring that typically contains 6 to 10 atoms in the ring portion containing one or more heteroatoms. A heteroaryl group is generally a 5- or 6-membered ring containing at least one heteroatom selected from O, S, N, P, Se and Si. It may contain, for example, one, two or three heteroatoms. Examples of heteroaryl groups include pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, furanyl, thienyl, pyrazolidinyl, pyrrolyl, oxazolyl, oxadiazolyl, isoxazolyl, thiadiazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl, quinolyl and isoquinolyl.

[0039] The term "substituted" as used herein in the context of substituted organic groups means C 1-10 Alkyl, aryl (as defined herein), cyano, amino, nitro, C 1-10 Alkylamino, di(C 1--10 ) Alkylamino, arylamino, diarylamino, aryl(C 1--10 ) Alkylamino, Amido, Acyl Amido, Hydroxy, Oxo, Halo, Carboxy, Ester, Acyl, Acyloxy, C 1-10 Alkoxy, aryloxy, halo(C 1--10 ) Alkyl, Sulfonic Acid, Thiol, C 1-10 It refers to an organic group having one or more substituents selected from alkylthio, arylthio, sulfonyl, phosphoric acid, phosphate ester, phosphonic acid, and phosphonate ester. Examples of substituted alkyl groups include haloalkyl, perhaloalkyl, hydroxyalkyl, aminoalkyl, alkoxyalkyl, and alkaryl groups. When a group is substituted, it can have one, two, or three substituents. For example, a substituted group can have one or two substituents.

[0040] As used herein, the term "halide" refers to a monovalent anion of an element in Group VIII of the periodic table. "Halide" includes fluoride, chloride, bromide, and iodide.

[0041] The term "halo" as used herein refers to a halogen atom. Exemplary halo species include fluoro, chloro, bromo and iodo species.

[0042] As used herein, an amino group is a group of formula -NR2, where each R is a substituent. R is typically selected from hydrogen, alkyl, alkenyl, cycloalkyl, or aryl, where each of alkyl, alkenyl, cycloalkyl, and aryl is as defined herein. Typically, each R is selected from hydrogen, C 1-10 Alkyl, C 2-10 Alkenyl, and C 3-10 Preferably, each R is selected from hydrogen, C 1-6 Alkyl, C 2-6 Alkenyl, and C 3-6 More preferably, each R is selected from hydrogen and C 1-6 is selected from alkyl.

[0043] Exemplary amino groups are alkylamino groups of the formula -NR2, where at least one R is an alkyl group as defined herein. 1-6 An alkylamino group is one in which at least one R is C. 1-6 It is an alkylamino group which is an alkyl group.

[0044] As used herein, an imino group is a group of formula R2C=N- or -C(R)=NR, where each R is a substituent. That is, an imino group is a group that contains a C=N moiety, either having a group moiety at the N atom of the C=N bond or having a group moiety bonded to the C atom of the C=N bond. R is as defined herein; that is, R is typically selected from hydrogen, alkyl, alkenyl, cycloalkyl, or aryl, where each of alkyl, alkenyl, cycloalkyl, and aryl are as defined herein. Typically, each R is selected from hydrogen, C 1-10 Alkyl, C 2-10 Alkenyl, and C 3-10Preferably, each R is selected from hydrogen, C 1-6 Alkyl, C 2-6 Alkenyl, and C 3-6 More preferably, each R is selected from hydrogen and C 1-6 is selected from alkyl.

[0045] Exemplary imino groups are alkylimino groups of formula R2C=N- or -C(R)=NR, where at least one R is an alkyl group as defined herein. 1-6 An alkylimino group is one in which the R substituent contains from 1 to 6 carbon atoms.

[0046] The term "ester" as used herein refers to an organic compound of the formula alkyl-C(=O)-O-alkyl, where the alkyl groups are the same or different and are as defined herein. The alkyl groups may be optionally substituted.

[0047] As used herein, the term "ammonium" refers to an organic cation that contains a quaternary nitrogen. The ammonium cation has the formula R 1 R 2 R 3 R 4 N + R is a cation of 1 , R 2 , R 3 , and R 4 is a substituent. 1 , R 2 , R 3 , and R 4 are typically independently selected from hydrogen or optionally substituted alkyl, alkenyl, aryl, cycloalkyl, cycloalkenyl, and amino; any optional substituents are preferably amino or imino substituents. 1 , R 2 , R 3 , and R 4 Each of 1-10 Alkyl, C 2-10 Alkenyl, C3-10 Cycloalkyl, C 3-10 Cycloalkenyl, C 6-12 Aryl and C 1-6 When present, the optional substituents are preferably amino groups; particularly preferably C 1-6 Preferably, R 1 , R 2 , R 3 , and R 4 Each of the groups is hydrogen and unsubstituted C 1-10 Alkyl, C 2-10 Alkenyl, C 3-10 Cycloalkyl, C 3-10 Cycloalkenyl, C 6-12 Aryl and C 1-6 In a particularly preferred embodiment, R 1 , R 2 , R 3 , and R 4 is hydrogen, C 1-10 Alkyl, and C 2-10 Alkenyl and C 1-6 More preferably, R 1 , R 2 , R 3 , and R 4 is hydrogen, C 1-6 Alkyl, C 2-6 Alkenyl and C 1-6 are independently selected from amino.

[0048] As used herein, the term “iminium” refers to a compound of the formula (R 1 R 2 C=NR 3 R 4 ) + , in the formula R 1 , R 2 , R 3 , and R 4 represents an organic cation as defined for the ammonium cation. Thus, in a particularly preferred embodiment of the iminium cation, R 1 , R 2 , R 3 , and R 4 is hydrogen, C1-10 Alkyl, C 2-10 Alkenyl and C 1-6 In a further preferred embodiment of the iminium cation, R 1 , R 2 , R 3 , and R 4 is hydrogen, C 1-6 Alkyl, C 2-6 Alkenyl and C 1-6 Frequently, the iminium cation is a formamidinium, i.e., R 1 is NH2, and R 2 , R 3 and R 4 are all H.

[0049] As used herein, the term "optoelectronic device" refers to a device that generates, controls, or detects light. Light is understood to include any electromagnetic radiation. Examples of optoelectronic devices include photovoltaic devices, photodiodes (including solar cells), phototransistors, photomultipliers, photoresistors, and light-emitting diodes.

[0050] The term "consisting essentially of" refers to a composition that contains the component it substantially comprises as well as other components, provided that the other components do not substantially affect the essential properties of the composition. Typically, a composition that consists essentially of certain components contains 95 wt% or more of those components, or 99 wt% or more of those components.

[0051] As used herein, the term "disposed on" or "disposed on" refers to making one component available on or placing on another component. A first component can be made available on or placed directly on a second component, or there can be a third component intervening between the first and second components. For example, when a first layer is placed on a second layer, this includes the case where there is a third intervening layer between the first and second layers. Typically, "disposed on" refers to placing one component directly on the other component.

[0052] The term "layer" as used herein refers to any structure that is substantially laminar in form (e.g., extends substantially in two perpendicular directions, but its extension in a third perpendicular direction is limited). A layer may have a thickness that varies over the extent of the layer. Typically, a layer has an approximately constant thickness. The "thickness" of a layer as used herein refers to the average thickness of the layer. The thickness of a layer can be readily measured, for example, by microscopy, such as electron microscopy of a cross-section of a film, or by surface profilometry using a stylus profilometer.

[0053] The term "band gap" as used herein refers to the energy difference between the top of the valence band and the bottom of the conduction band in a material. Those skilled in the art can easily measure the band gap of a semiconductor (including perovskite semiconductors) by using well-known procedures that do not require undue experimentation. For example, the band gap of a semiconductor can be estimated by constructing a photovoltaic diode or solar cell from the semiconductor and determining the photovoltaic action spectrum. Alternatively, the band gap can be estimated by measuring the optical absorption spectrum by either transmission spectrophotometry or photothermal deflection spectroscopy. The band gap can be determined by constructing a Tauc plot as described in Tauc, J., Grigorovici, R. & Vancu, a. Optical Properties and Electronic Structure of Amorphous Germanium. Phys. Status Solidi 15, 627-637 (1966), where the square of the product of the absorption coefficient and the photon energy is plotted on the Y-axis against the photon energy on the x-axis, with a linear intercept at the absorption edge, and the x-axis gives the optical band gap of the semiconductor. Alternatively, the optical band gap can be estimated by taking the onset of the incident photon to electron conversion efficiency as described in [Barkhouse DAR, Gunawan O, Gokmen T, Todorov TK, Mitzi DB. Device characteristics of a 10.1% hydrazineprocessed Cu2ZnSn(Se,S)4 solar cell. Progress in Photovoltaics: Research and Applications 2012; published online DOI: 10.1002 / pip.1160.].

[0054] As used herein, the term "semiconductor" or "semiconductor material" refers to a material that has an electrical conductivity intermediate between that of a conductor and that of a dielectric. A semiconductor can be a negative (n)-type semiconductor, a positive (p)-type semiconductor, or an intrinsic (i) semiconductor. A semiconductor can have a band gap of 0.5 to 3.5 eV, e.g., 0.5 to 2.5 eV or 1.0 to 2.0 eV (measured at 300 K).

[0055] As used herein, the term "n-type region" refers to a region of one or more electron transporting (i.e., n-type) materials. Similarly, the term "n-type layer" refers to a layer of an electron transporting (i.e., n-type) material. An electron transporting (i.e., n-type) material can be a single electron transporting compound or elemental material, or a mixture of two or more electron transporting compounds or elemental materials. An electron transporting compound or elemental material can be undoped or doped with one or more dopant elements.

[0056] As used herein, the term "p-type region" refers to a region of one or more hole-transporting (i.e., p-type) materials. Similarly, the term "p-type layer" refers to a layer of a hole-transporting (i.e., p-type) material. A hole-transporting (i.e., p-type) material can be a single hole-transporting compound or elemental material, or a mixture of two or more hole-transporting compounds or elemental materials. A hole-transporting compound or elemental material can be undoped or doped with one or more dopant elements.

[0057] As used herein, the term "electrode material" refers to any material suitable for use in an electrode. The electrode material has high electrical conductivity. As used herein, the term "electrode" refers to a region or layer that consists or consists essentially of an electrode material.

[0058] As used herein, the term "chalcogenide" or "chalcogenide anion" refers to an oxygen (O 2- ), Sulfur (S 2- ), Selenium (Se 2- ) or Tellurium (Te 2-) anion.

[0059] The term "transition metal" as used herein means any one of the three rows of elements resulting from the filling of the 3d, 4d and 5d shells and located in the periodic table following the alkaline earth metals. This definition is used for the term "transition element" in NN Greenwood and A. Earnshaw "Chemistry of the Elements", First Edition 1984, Pergamon Press Ltd., page 1060, paragraph 1. The same definition is used herein for the term "transition metal". Thus, the term "transition metal" as used herein includes all of Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd and Hg. These are also referred to as first, second and third row transition metals (i.e., transition metals in the fourth, fifth and sixth rows of the periodic table).

[0060] The term "p-block metal" as used herein means any metal in the p-block of the periodic table. Thus, as used herein, the term "p-block metal" refers to a metal selected from Al, Ga, Ge, In, Tl, Sn, Sb, Tl, Pb, and Bi.

[0061] Multijunction Devices The present invention relates to a) a first photoactive region comprising a layer of a first photoactive material; b) a second photoactive region comprising a layer of a second photoactive material; and c) a charge recombination layer disposed between the first photoactive region and the second photoactive region, where the charge recombination layer comprises a charge recombination layer material; wherein one of the first and second photoactive materials comprises at least one A / M / X material; and wherein the other of the first and second photoactive materials comprises at least one A / M / X material or a compound that is a photoactive semiconductor other than an A / M / X material; and wherein each A / M / X material is a crystalline compound of formula (I), [A] a [M] b [X] c (I) wherein: [A] comprises one or more A cations; [M] comprises one or more M cations which are metal or semi-metal cations; [X] comprises one or more X anions; a is a number from 1 to 6; b is a number from 1 to 6; and c is a number from 1 to 18; and wherein the charge recombination layer material has a refractive index, n(λ), of at least 2 at a wavelength λ, where λ is a wavelength between 500 nm and 1200 nm. A multijunction device is provided.

[0062] Thus, the refractive index n(λ) of the charge recombination layer material can be at least 2 at a single wavelength λ, where λ is a wavelength between 500 nm and 1200 nm. In other words, the requirement is met if n(λ) is at least 2 at at least one wavelength λ in the range of 500 nm to 1200 nm (this range including both endpoints of 500 nm and 1200 nm).

[0063] In practice, the refractive index n(λ) of the charge recombination layer material is often at least 2 over more than one wavelength in the range of 500 nm to 1200 nm. It can be, for example, at least 2 over a range of wavelengths in the range of 500 nm to 1200 nm.

[0064] In some embodiments, the refractive index, n(λ), of the charge recombination layer material can be at least 2 for all wavelengths in the range of 500 nm to 1200 nm.

[0065] Typically, the charge recombination layer material has a low absorption coefficient α, e.g., α<10 at wavelengths typically between 650-1100 nm. 3 cm -1 Typically, the charge recombination layer material has a low resistivity, e.g., 10 5 <10 Ω cm 4 <10 Ω cm 3In one embodiment, the charge recombination layer material has a resistivity of less than 10 Ω cm, less than 500 Ω cm, less than 250 Ω cm, less than 100 Ω cm, less than 50 Ω cm, less than 10 Ω cm, less than 5 Ω cm, or less than 1 Ω cm. 5 Ω cm to 0.1 Ω cm range, or 10 5 Ω cm to 1 Ω cm, more preferably 10 3 It has a resistivity in the range of Ω cm to 10 Ω cm.

[0066] Due to the risk of shorting the device by undesired contact of the top electrode with the recombination layer, it is advantageous if the recombination layer has an intermediate resistivity. Ideally, the resistivity should be low enough to allow low-voltage loss recombination of carriers from the top and bottom subcells, but high enough not to short out most of the device if the top contact comes into physical contact with the recombination layer. In thin-film photovoltaic modules, this event can occur in the interconnection between different strings in the module, as described by Walter et al. [Walter et al. Closing the Cell-to-Module Efficiency Gap: A Fully Laser Scribed Perovskite Minimodule with 16% Steady-State Aperture Area Efficiency IEEE Journal of Photovoltaics, Vol 8, No. 1, January 2018], where scribing and interconnection require the top electrode of one string to be in physical and electronic contact with the bottom electrode of the adjacent string. Therefore, a further challenge to be overcome before a successful perovskite tandem module can be fabricated is to find a chemically impermeable recombination layer with intermediate resistivity.

[0067] The charge recombination layer may include a charge recombination layer material having a refractive index n(λ) of at least 2 at a wavelength λ, where λ is a wavelength between 500 nm and 1200 nm, and optionally one or more additional layers. Typically, the charge recombination layer consists essentially of or consists of a charge recombination layer material having a refractive index n(λ) of at least 2 at a wavelength λ, where λ is a wavelength between 500 nm and 1200 nm.

[0068] Charge recombination layer materials typically have a refractive index n(λ) of at least 2 at a wavelength λ, where λ is a wavelength between 500 nm and 1100 nm, between 600 nm and 1200 nm, between 550 nm and 1150 nm, between 600 nm and 1100 nm, between 600 and 1000 nm, or between 700 nm and 1000 or preferably between 800 nm and 1000 nm. For example, charge recombination layer materials may have a refractive index n(λ) of at least 2 at a wavelength λ, where λ is a wavelength between about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, about 1000 nm, about 1050 nm, about 1100 nm, about 1150 nm, or about 1200 nm. Often, the charge recombination layer material has a refractive index n(λ) of at least 2 at a wavelength λ, where λ is a wavelength between 800 nm and 900 nm. Typically, the charge recombination layer material has a refractive index n(λ) of at least 2 at a wavelength λ, where λ is a wavelength of 850 nm.

[0069] Typically, the refractive index n(λ) of the charge recombination layer material at a wavelength λ is less than 3.5, optionally less than or equal to 3, and more particularly less than or equal to 2.5, where λ is a wavelength between 500 nm and 1200 nm. Typically, the charge recombination layer material may have a refractive index n(λ) of at least 2 and less than 3 at a wavelength λ, where λ is a wavelength between 500 nm and 1200 nm, or between 600 nm and 1200 nm, for example between 550 nm and 1150 nm, 600 nm and 1100 nm, 700 nm and 1000 nm, or between 800 nm and 1000 nm, for example between 800 nm and 900 nm, for example about 850 nm. For example, the charge recombination layer material may have a refractive index n(λ) of at least 2 and less than 2.75 at a wavelength λ, where λ is a wavelength between 500 nm and 1200 nm, or between 600 nm and 1200 nm, e.g., between 550 nm and 1150 nm, between 600 nm and 1100 nm, or between 700 nm and 1000 nm, or between 800 and 1000 nm, e.g., between 800 nm and 900 nm, e.g., about 850 nm. Preferably, the charge recombination layer material has a refractive index n(λ) of at least 2 and less than 2.5 at a wavelength λ, where λ is a wavelength between 500 nm and 1200 nm, or between 600 nm and 1200 nm, for example between 550 nm and 1150 nm, between 600 nm and 1100 nm, or between 700 nm and 1000 nm, or between 800 and 1000 nm, for example between 800 nm and 900 nm, for example about 850 nm.

[0070] Typically, the charge recombination layer material is A The refractive index n(λ A ), and the first photoactive material has a wavelength λ A The refractive index n1(λ A ), where n1(λ A ) is n(λ A ), where λ A is a wavelength between 500 nm and 1200 nm, which may be the same as or different from λ. Therefore, A n1(λ A ) <n(λ A ).

[0071] Typically, the first photoactive material emits light at a wavelength λ A A refractive index n1(λ) of at least 1, at least 1.5 or at least 2 A For example, the first photoactive material has a wavelength λ A The refractive index n1 (λ) is between 1 and 3, typically between 1.5 and 2.5, for example, between 1.5 and 2.0 or between 2.0 and 2.5. A ).

[0072] wavelength λ A is the same as λ, the charge recombination layer material is A A refractive index n(λ) of at least 2 A ) and the first photoactive material has a wavelength λ A n(λ A ) smaller than the refractive index n1(λ A ), where λ and λ A Both of n(λ) and n(λ) are wavelengths of 500 nm to 1200 nm or 600 nm to 1200 nm, for example, 550 nm to 1150 nm, 600 nm to 1100 nm, 700 nm to 1000 nm, or 800 nm to 1000 nm, for example, 800 nm to 900 nm. A )>2 and n(λ A )>n1(λ A ).

[0073] wavelength λ A can be different from λ. Thus, at one wavelength λ, the refractive index n(λ) of the charge recombination layer material is at least 2, and at another wavelength λ A The charge recombination layer material is A The refractive index n(λ A ), and the first photoactive material has a wavelength λ A The refractive index n1(λ A ), where n1(λ A ) is n(λ A ), where λ and λ ABoth of them have (different) wavelengths of 500 nm to 1200 nm, 600 nm to 1200 nm, for example 550 nm to 1150 nm, 600 nm to 1100 nm, 700 nm to 1000 nm, or 800 nm to 1000 nm, for example 800 nm to 900 nm.

[0074] The charge recombination layer material is A The refractive index n(λ A ), and the second photoactive material can have a wavelength λ A The refractive index n2(λ A ), where n2(λ A ) is n(λ A ), where λ A is a wavelength between 500 nm and 1200 nm, which may be the same as or different from λ. Therefore, A n2(λ A )>n(λ A ).

[0075] Typically, the second photoactive material emits light at wavelength λ A A refractive index n2(λ) of at least 1.5, or at least 2, or at least 2.5 A For example, the second photoactive material has a wavelength λ A The refractive index n2 (λ) is between 1.5 and 3.5, typically between 2 and 3, for example between 2 and 2.5 or between 2.5 and 3. A ).

[0076] wavelength λ A is the same as λ, the charge recombination layer material is A A refractive index n(λ) of at least 2 A ) and the second photoactive material has a wavelength λ A n(λ A ) is greater than n2(λ A ), where λ and λ ABoth of n(λ) and n(λ) are 500 nm to 1200 nm, 600 nm to 1200 nm, for example, 550 nm to 1150 nm, 600 nm to 1100 nm, 700 nm to 1000 nm, or 800 nm to 1000 nm. Thus, in this embodiment, n(λ) and n(λ) are 500 nm to 1200 nm, 600 nm to 1100 nm, 700 nm to 1000 nm, or 800 nm to 1000 nm. A )>2 and n(λ A ) <n2(λ A ).

[0077] wavelength λ A can be different from λ. Thus, at one wavelength λ, the refractive index n(λ) of the charge recombination layer material is at least 2, and at another wavelength λ A The charge recombination layer material is A The refractive index n(λ A ), and the second photoactive material has a wavelength λ A The refractive index n2(λ A ), where n(λ A ) is n(λ A ), where λ and λ A Both of them have (different) wavelengths of 500 nm to 1200 nm, 600 nm to 1200 nm, for example, 550 nm to 1150 nm, 600 nm to 1100 nm, 700 nm to 1000 nm, or 800 nm to 1000 nm.

[0078] Thus, typically, the charge recombination layer material is A The refractive index n(λ A ), and the first photoactive material has a wavelength λ A The refractive index n1(λ A ), and the second photoactive material has a wavelength λ A The refractive index n2(λ A ), where n1(λ A ) is n(λ A ), and n2(λ A ) is n(λ A ), where λ A is a wavelength between 500 nm and 1200 nm, which may be the same as or different from λ. Therefore, A n2(λ A )>n(λA )>n1(λ A ).

[0079] In the embodiments discussed above, typically, λ A λ is 500 nm to 1200 nm, 600 nm to 1200 nm, 500 to 1100 nm, 550 nm to 1150 nm, 600 nm to 1100 nm, 600 to 1000 nm, or 700 nm to 1000, or 800 nm to 1000 nm, for example, 800 nm to 900 nm. A can be about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, about 1000 nm, about 1050 nm, about 1100 nm, about 1150 nm or about 1200 nm. Typically, λ A is about 850 nm.

[0080] In the embodiments discussed above, typically, λ A and λ are the same wavelength. For example, λ A Both λ and λ can be the same wavelength, where the wavelength is 500 nm to 1200 nm, 600 nm to 1200 nm, 500 to 1100 nm, 550 nm to 1150 nm, 600 nm to 1100 nm, 600 to 1000 nm, or 700 nm to 1000, or 800 nm to 1000 nm, for example, 800 nm to 900 nm. A Both λ and λ can be about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, about 1000 nm, about 1050 nm, about 1100 nm, about 1150 nm or about 1200 nm. Typically, λ A and λ are both about 850 nm.

[0081] The charge recombination layer material is usually a semi-transparent material. Typically, the charge recombination layer material has an average light transmittance of about 50% or more, for example, about 60% or more, about 70% or more, about 80% or more, about 90% or more in the visible to near infrared range of the spectrum. It may, for example, have an average light transmittance of 50% to 90%, for example, 60% to 85%, for example, 70% to 80%, or for example, 80% to 95%, for example, 90% to 95% in the visible range of the spectrum. The visible range of the spectrum is usually understood to be about 400 nm to about 700 nm. Preferably, the charge recombination layer material is semi-transparent to wavelengths in the range of 700 to 1100 nm. For example, the charge recombination layer material has an average light transmittance of about 50% or more, for example, about 60% or more, about 70% or more, about 80% or more, or about 90% or more in the spectral range of 700 nm to 1100 nm. It may for example have an average light transmittance in the spectral range from 700 nm to 1100 nm of 50% to 90%, such as 60% to 85%, for example 70% to 80%, or such as 80% to 95%, for example 90% to 95%.

[0082] Typically, the charge recombination layer material has a band gap of at least 2 eV, at least 2.5 eV or at least 3 eV, for example at least 3.2 eV, or at least 3.5 eV. Thus, typically, the charge recombination layer material is a wide band gap semiconductor.

[0083] Typically, the first photoactive material has a bandgap Eg1 and the second photoactive material has a bandgap Eg2, where Eg1 is greater than Eg2 (Eg1>Eg2). Typically, both Eg1 and Eg2 are 3 eV or less, e.g., 2.8 eV or less, 2.5 eV or less, 2.3 eV or less, or 2.0 eV or less.

[0084] Typically, the first photoactive material has a bandgap Eg1, and the charge recombination layer material has a bandgap Eg, where Eg is greater than Eg1. Thus, typically Eg>Eg1.

[0085] Typically, the charge recombination layer material has a bandgap Eg, the first photoactive material has a bandgap Eg1, and the second photoactive material has a bandgap Eg2, where Eg is greater than Eg1 and Eg1 is greater than Eg2, thus typically Eg>Eg1>Eg2.

[0086] Typically, Eg is at least 2.0 eV, for example, Eg can be at least 3.0 eV, and Eg1 can be 3.0 eV or less, 2.8 eV or less, 2.5 eV or less, 2.3 eV or less, or 2.0 eV or less. Eg can be, for example, at least 3.2 eV, or at least 3.5 eV.

[0087] Typically, the charge recombination layer has a thickness of at least 5 nm, for example, a thickness of 20 to 300 nm, or a thickness of 20 to 200 nm, more particularly a thickness of 50 to 200 nm, or a thickness of 75 to 150 nm, or a thickness of 80 to 125 nm, or a thickness of 90 to 110 nm. For example, the charge recombination layer may have a thickness of about 100 nm.

[0088] The charge recombination layer is

[0089]

number

[0090] λ in the formula o is a wavelength between 500 nm and 1200 nm that may be the same or different from λ, and n is the λ of the charge recombination layer material. o is the refractive index at The thickness of the film may be in the range of 1 nm to 2 nm.

[0091] For example, the charge recombination layer is

[0092]

number

[0093] λ in the formula ois a wavelength between 500 nm and 1200 nm that may be the same or different from λ, and n is the λ of the charge recombination layer material. o is the refractive index at The thickness of the film may be in the range of 1 nm to 2 nm.

[0094] There are also other thicknesses of the charge recombination layer that result in minimal reflection losses. In one embodiment, the charge recombination layer is

[0095]

number

[0096] λ in the formula o is a wavelength between 500 nm and 1200 nm that may be the same or different from λ, and n is the λ of the charge recombination layer material. o is the refractive index at The thickness of the film may be in the range of 1 nm to 2 nm.

[0097] In another embodiment, the charge recombination layer comprises

[0098]

number

[0099] λ in the formula o is a wavelength between 500 nm and 1200 nm that may be the same or different from λ, and n is the λ of the charge recombination layer material. o is the refractive index at The thickness of the film may be in the range of 1 nm to 2 nm.

[0100] In the embodiments discussed above, typically, λ ois 500 nm to 1200 nm, 600 nm to 1200 nm, 500 to 1100 nm, 550 nm to 1150 nm, 600 nm to 1100 nm, 600 to 1000 nm, or 700 nm to 1000, or 800 nm to 1000 nm, for example 800 nm to 900 nm. λ0 can be about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, about 1000 nm, about 1050 nm, about 1100 nm, about 1150 nm or about 1200 nm. Typically, λ o is about 850 nm.

[0101] Typically, λ o is the same as λ. For example, λ0 and λ can both be the same wavelength, where the wavelength is 500 nm to 1200 nm, 600 nm to 1200 nm, for example, 550 nm to 1150 nm, 600 nm to 1100 nm, or 700 nm to 1000 nm, for example, 800 nm to 900 nm. λ0 and λ can both be about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, about 1000 nm, about 1050 nm, about 1100 nm, about 1150 nm, or about 1200 nm.

[0102] Typically, one of the first and second photoactive materials comprises at least one A / M / X material described herein, and the other of the first and second photoactive materials comprises a compound that is a photoactive semiconductor other than an A / M / X material. For example, one of the first and second photoactive materials can consist essentially of, or consist of, at least one A / M / X material described herein, and the other of the first and second photoactive materials can consist essentially of, or consist of, a compound that is a photoactive semiconductor other than an A / M / X material.

[0103] Typically, the first photoactive material comprises at least one A / M / X material described herein, and the second photoactive material comprises a compound that is a photoactive semiconductor other than an A / M / X material. For example, the first photoactive material can consist essentially of, or consist of, at least one crystalline A / M / X material described herein, and the second photoactive material can consist essentially of, or consist of, a compound that is a photoactive semiconductor other than an A / M / X material.

[0104] Alternatively, the first photoactive material can include a compound that is a photoactive semiconductor other than an A / M / X material, and the second photoactive material can include at least one A / M / X material described herein. For example, the first photoactive material can consist essentially of or consist of a compound that is a photoactive semiconductor other than an A / M / X material, and the second photoactive material can consist essentially of at least one A / M / X material described herein.

[0105] In some embodiments, the multijunction device may include a third photoactive region comprising a layer of a third material. The third photoactive material may be as described herein for the first and second photoactive materials. For example, the third photoactive material may comprise, consist essentially of, or consist of at least one A / M / X material described herein. The third photoactive material may comprise, consist essentially of, or consist of a compound that is a photoactive semiconductor other than the A / M / X material. For example, the third photoactive material may comprise, consist essentially of, or consist of a compound that is a photoactive semiconductor other than the A / M / X material described herein. Materials that are photoactive semiconductors other than the A / M / X material are known to those skilled in the art. Such materials include silicon-based materials such as crystalline silicon (c-Si) and compounds that are photoactive semiconductors other than the A / M / X material described herein.

[0106] In one embodiment, each of the first, second and third photoactive materials comprises at least one A / M / X material described herein. Each of the first, second and third photoactive materials can comprise a different A / M / X material described herein.

[0107] In one embodiment, each of the first and second photoactive materials includes at least one A / M / X material described herein, and the third photoactive material includes a material that is a photoactive semiconductor other than an A / M / X material. For example, each of the first and second photoactive materials includes at least one A / M / X material described herein, and the third photoactive material includes a compound that is a photoactive semiconductor other than an A / M / X material described herein.

[0108] In one embodiment, one of the first and second photoactive materials comprises at least one A / M / X material described herein, the other of the first and second photoactive materials comprises a compound that is a photoactive semiconductor other than an A / M / X material, and the third photoactive material comprises a material that is a photoactive semiconductor other than an A / M / X material, e.g., a compound that is a photoactive semiconductor other than an A / M / X material described herein.

[0109] Typically, in embodiments where a layer of a third photoactive material is present, the device includes a second charge recombination layer. The second charge recombination layer can be as defined elsewhere herein for a charge recombination layer. The second charge recombination layer can be the same as or different from the charge recombination layer. The second charge recombination layer can include a charge recombination layer material as defined herein. The second charge recombination layer can include the same charge recombination layer material as the charge recombination layer. Alternatively, the second charge recombination layer can include a charge recombination layer material that is different from the charge recombination layer material that the charge recombination layer includes.

[0110] Materials that are photoactive semiconductors other than A / M / X materials Photoactive semiconductors other than A / M / X materials are known to those skilled in the art. Typically, compounds that are photoactive semiconductors contain chalcogenide anions. Typically, compounds that are photoactive semiconductors are metal chalcogenides and contain at least one metal and at least one chalcogenide anion. Metal chalcogenides can contain at least two different metals and at least one chalcogenide anion. Metal chalcogenides can contain at least two different metals and at least two different chalcogenide anions.

[0111] Typically, the metals are selected from transition metals and p-block metals. For example, the metal can be selected from gallium, niobium, tantalum, tungsten, indium, neodinium, palladium, copper, lead, antimony, zinc, iron, or bismuth.

[0112] Typically, the photoactive semiconductor compounds are selected from copper zinc tin chalcogenides, antimony chalcogenides, bismuth chalcogenides, copper indium gallium chalcogenides, cadmium chalcogenides, iron chalcogenides, and lead chalcogenides. Further examples are group IV compound semiconductors; group III-V semiconductors (e.g., gallium arsenide); group II-VI semiconductors (e.g., cadmium selenide); group I-VII semiconductors (e.g., cuprous chloride); group IV-VI semiconductors (e.g., lead selenide); group V-VI semiconductors (e.g., bismuth telluride); and group II-V semiconductors (e.g., cadmium hydride).

[0113] For example, the photoactive semiconductor compound is copper indium gallium selenide (CIGS), copper indium sulfide (CIS), copper indium gallium (S) selenide (CIG(S)Se), cadmium telluride (CdTe), cadmium telluride selenide (CdTe x Se 1-x , where 0 < x < 1), cadmium telluride sulfide (CdTe x S 1-x, where 0 < x < 1), and can be selected from copper zinc tin sulfide (CZTS), copper zinc tin selenide (CZTSe), copper zinc tin sulfoselenide (CZTSSe), antimony sulfide, antimony selenide, bismuth sulfide, bismuth selenide, iron sulfide, lead sulfide, lead selenide, cadmium sulfide, and cadmium selenide.

[0114] Preferably, the photoactive semiconductor compound is copper indium gallium selenide (CIGS), copper indium sulfide (CIS), copper indium sulfoselenide (CIG(S)Se), cadmium telluride (CdTe), cadmium tellurosulfide (CdTe x Se 1-x , where 0 < x < 1), cadmium tellurosulfide (CdTe x S 1-x , where 0 < x < 1), and is selected from copper zinc tin sulfide (CZTS), copper zinc tin selenide (CZTSe), and copper zinc tin sulfoselenide (CZTSSe). For example, the photoactive semiconductor compound is copper indium gallium selenide (CIGS), cadmium telluride (CdTe), cadmium tellurosulfide (CdTe x Se 1-x , where 0 < x < 1) or cadmium tellurosulfide (CdTe x S 1-x , where 0 < x < 1) can be.

[0115] Typically, the photoactive semiconductor has a bandgap of less than 3.0 eV, for example, less than 2.5 eV or less than 2.0 eV. The photoactive semiconductor can have a bandgap of at least 0.5 eV, at least 0.8 eV, or at least 1.0 eV. Typically, the photoactive semiconductor has a bandgap between 1.0 eV and 2.0 eV, for example, between 1.0 eV and 1.5 eV, or between 1.5 eV and 2.0 eV.

[0116] When the first photoactive material comprises at least one crystalline A / M / X material described herein, and the second photoactive material comprises a compound that is a photoactive semiconductor other than an A / M / X material, typically the first A / M / X material has a band gap Eg1 and the second photoactive material has a band gap Eg2, where Eg1 is greater than Eg2 (Eg1>Eg2). Typically, both Eg1 and Eg2 are 3.0 eV or less, e.g., 2.5 eV or less or 2.0 eV or less.

[0117] For example, Eg1 can be 1.5 eV or more, and Eg2 can be 1.5 eV or less. Typically, Eg1 is between 1.5 eV and 3 eV, for example, between 1.5 eV and 2.5 eV or between 1.5 eV and 2 eV. Typically, Eg2 is between 0.5 eV and 1.5 eV, for example, between 0.75 eV and 1.5 eV, between 0.75 eV and 1.25 eV, or between 1 eV and 1.5 eV. Eg1 can be about 1.5 eV, 1.6 eV, 1.7 eV, 1.8 eV, 1.9 eV, or 2.0 eV. Eg2 can be about 1 eV, 1.1 eV, 1.2 eV, 1.3 eV, 1.4 eV, or 1.5 eV. For example, Eg1 can be between 1.5 eV and 2.0 eV and Eg2 can be between 1 eV and 1.5 eV, such as between 1 eV and 1.2 eV.

[0118] Typically, the first photoactive material, which includes at least one crystalline A / M / X material, has a bandgap Eg1, and the charge recombination layer material has a bandgap Eg, where Eg is greater than Eg1. Thus, typically Eg>Eg1.

[0119] Typically, the charge recombination layer material has a band gap Eg, the first photoactive material comprising at least one crystalline A / M / X material has a band gap Eg1, and the second photoactive material comprising a compound that is a photoactive semiconductor other than the A / M / X material has a band gap Eg2, where Eg is greater than Eg1 and Eg1 is greater than Eg2. Thus, typically Eg>Eg1>Eg2. Usually, Eg is at least 2.0 eV, for example, Eg can be at least 3.0 eV, and Eg1 can be 2.0 eV or less.

[0120] The first and second photoactive materials are both A / M / X materials. Typically, the first photoactive material comprises at least one first A / M / X material described herein, and the second photoactive material comprises at least one second A / M / X material described herein. Typically, the first photoactive material consists essentially of or consists of at least one first A / M / X material described herein, and the second photoactive material consists essentially of or consists of at least one second A / M / X material described herein. Preferably, the at least one first and second crystalline A / M / X materials are different.

[0121] Typically, at least one of the first and second crystalline A / M / X materials have different bandgaps. Typically, when the first photoactive material comprises at least one first A / M / X material described herein and the second photoactive material comprises at least one second A / M / X material described herein, the first A / M / X material has a bandgap Eg1 and the second A / M / X material has a bandgap Eg2, where Eg1 is greater than Eg2 (Eg1>Eg2). Typically, both Eg1 and Eg2 are 3.0 eV or less, e.g., 2.5 eV or less or 2.0 eV or less.

[0122] For example, Eg1 can be 1.5 eV or more, and Eg2 can be 1.5 eV or less. Typically, Eg1 is between 1.5 eV and 3 eV, for example, between 1.5 eV and 2.5 eV or between 1.5 eV and 2 eV. Typically, Eg2 is between 0.5 eV and 1.5 eV, for example, between 0.75 eV and 1.5 eV or between 1 eV and 1.5 eV. Eg1 can be about 1.5 eV, 1.6 eV, 1.7 eV, 1.8 eV, 1.9 eV or 2.0 eV. Eg2 can be about 1 eV, 1.1 eV, 1.2 eV, 1.3 eV, 1.4 eV or 1.5 eV. For example, Eg1 can be between 1.5 eV and 2.0 eV, and Eg2 can be between 1 eV and 1.5 eV.

[0123] Typically, the first A / M / X material has a bandgap Eg1 and the charge recombination layer material has a bandgap Eg, where Eg is greater than Eg1. Thus, typically, Eg>Eg1.

[0124] Typically, the charge recombination layer material has a band gap Eg, the first A / M / X material has a band gap Eg1, and the second A / M / X material has a band gap Eg2, where Eg is greater than Eg1, and Eg1 is greater than Eg2. Thus, typically Eg>Eg1>Eg2. Usually, Eg is at least 2.0 eV, for example, Eg can be at least 3.0 eV, and Eg1 can be 2.0 eV or less.

[0125] Charge recombination layer material The charge recombination layer material can be an organic or inorganic material. Preferably, the charge recombination layer material is an inorganic material. In general, inorganic materials are less susceptible to damage by the application of solvents when constructing the layer.

[0126] Typically, the charge recombination layer material includes a metal oxide, a metal nitride, or a metal sulfide. For example, the charge recombination layer material may include TiO2, metal-doped TiO2, SrTiO3, BaTiO3, Cr2O3, CuCrO2, ZnS, ZrO2, AlN, GaN, and TiN. Preferably, the charge recombination layer material includes TiO2 or metal-doped TiO2.

[0127] Typically, the charge recombination layer material comprises (a) TiO2 or metal-doped TiO2 and (b) a transparent conductive oxide. Preferably, the charge recombination layer material comprises a mixture of (a) and (b). The transparent conductive oxide may be selected from fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO) and indium-doped tin oxide (ITO). Usually, the transparent conductive oxide is indium tin oxide (ITO).

[0128] Typically, when the charge recombination layer material comprises a mixture of (a) and (b), the TiO2 or metal-doped TiO2 is at least 20% by volume of the combined volume of the transparent conductive oxide and the TiO2 or metal-doped TiO2. For example, the TiO2 or metal-doped TiO2 can be at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% by volume of the combined volume of the transparent conductive oxide and the TiO2 or metal-doped TiO2.

[0129] The charge recombination layer material typically comprises metal-doped TiO2. The metal is usually a transition metal. Typically, the transition metal is selected from Ta, V and Nb. Preferably, the transition metal is Nb.

[0130] The metal in the metal-doped TiO2 may be present in an amount of at least 0.5 wt% of the total weight of the metal-doped TiO2. For example, the metal in the metal-doped TiO2 may be present in an amount of at least 1 wt% of the total weight of the metal-doped TiO2. Typically, the metal in the metal-doped TiO2 may be present in an amount of 1-10 wt% of the total weight of the metal-doped TiO2, or in an amount of 2-6 wt% of the total weight of the metal-doped TiO2. Thus, in one embodiment, the metal in the metal-doped TiO2 is Ta, V or Nb, preferably Nb, in an amount of 1-10%, for example, 2-6 wt% of the total weight of the metal-doped TiO2.

[0131] The charge recombination layer material may include a mixture of metal-doped TiO2, where the metal is selected from Ta, V or Nb, preferably Nb, and a transparent conductive oxide. The metal-doped TiO2, preferably Nb-doped TiO2, is at least 20% by volume of the total volume of the transparent conductive oxide and the metal-doped TiO2. For example, the metal-doped TiO2, preferably Nb-doped TiO2, may be at least 30% by volume, at least 40% by volume, at least 50% by volume, at least 60% by volume, at least 70% by volume, at least 80% by volume, or at least 90% by volume of the total volume of the transparent conductive oxide and the metal-doped TiO2.

[0132] Titanium dioxide can be in any amorphous or crystalline form. Thus, it can be, for example, in the anatase, rutile or brookite form. Typically, in charge recombination layers that include TiO2, the TiO2 is in the rutile phase.

[0133] Thus, in one embodiment, the charge recombination layer comprises TiO2 in the rutile phase doped with a transition metal selected from Ta, V and Nb, preferably Nb, in an amount of 1-10 wt%, 2-6 wt%, e.g., about 4 wt% of the total weight of the metal-doped TiO2.

[0134] The charge recombination layer material may consist essentially of or may consist of TiO2 or metal-doped TiO2. The charge recombination layer material may consist essentially of or may consist of metal-doped TiO2. The metal is usually a transition metal. Typically, the transition metal is selected from Ta, V and Nb. Typically, the transition metal is Nb. Typically, the metal, preferably Nb, is present in an amount of 1-10 wt%, 2-6 wt%, for example, about 4 wt% of the total weight of the metal-doped TiO2. Thus, the charge recombination layer material may consist essentially of or may consist of Nb-doped TiO2, where Nb is present in an amount of 1-10 wt%, 2-6 wt%, for example, about 4 wt% of the total weight of the metal-doped TiO2.

[0135] In one embodiment, the charge recombination layer comprises a layer of charge recombination layer material and one or more additional layers. For example, the charge recombination layer may comprise a layer of charge recombination layer material and two additional layers. The additional layer may be a layer of transparent conductive oxide, which may be selected from, for example, fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO) and indium-doped tin oxide (ITO). Typically, the additional layer is a layer of indium tin oxide (ITO). Thus, the charge recombination layer may comprise the following layers in the following order: - an additional layer of a transparent conductive oxide, preferably ITO; - a layer of a charge recombination layer material as described herein; -An additional layer of transparent conductive oxide, preferably ITO.

[0136] Typically, each of the additional layers has a thickness of less than 100 nm, less than 50 nm, less than 25 nm, less than 10 nm, preferably about 5 nm. Typically, the charge recombination layer material is TiO2 or metal-doped TiO2 as described herein. The layer of the charge recombination layer can have any thickness as described herein. Typically, the layer of the charge recombination layer material is 20 to 300 nm, for example 20 to 200 nm.

[0137] Thus, the charge recombination layer can comprise, consist essentially of, or consist of the following layers in the following order: - additional layer of ITO; - a layer of TiO2 or metal-doped TiO2 as described herein; -An additional layer of ITO.

[0138] A / M / X materials Thus, the multijunction devices of the present invention include at least one layer of photoactive material comprising at least one crystalline A / M / X material having the formula: [A] a [M] b [X] c includes compounds of the formula: [A] comprises one or more A cations; [M] comprises one or more M cations which are metal or metalloid cations; [X] comprises one or more X anions; a is a number from 1 to 6; b is a number from 1 to 6; and c is a number from 1 to 18. A is often a number from 1 to 4, b is often a number from 1 to 3, and c is often a number from 1 to 8.

[0139] Each of a, b and c may be an integer or may not be an integer. For example, a, b or c may not be an integer if the compound adopts a structure with vacancies such that the crystal lattice is not completely filled. The method of the present invention provides very good control over the stoichiometry of the product, and is therefore well suited to forming structures in which a, b or c are not integers (e.g., structures with vacancies at one or more of the A, M or X sites). Thus, in some embodiments, one or more of a, b and c are non-integer values. For example, one of a, b and c can be non-integer values. In one embodiment, a is a non-integer value. In another embodiment, b is a non-integer value. In yet another embodiment, c is a non-integer value.

[0140] In other embodiments, each of a, b, and c is an integer value. Thus, in some embodiments, a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18. A is often an integer from 1 to 4, b is often an integer from 1 to 3, and c is often an integer from 1 to 8.

[0141] Formula [A] a [M] b [X] c In the compound of formula (I), generally: [A] contains one or more A cations, which may be selected, for example, from alkali metal cations or organic monocations; [M] is Pd 4+ , W 4+ , Re 4+ , Os 4+ , Ir 4+ , Pt 4+ , Sn 4+ , Pb 4+ , Ge 4+ , Te 4+ , Bi 3+ , Sb 3+ , Ca 2+ , Sr 2+ , Cd 2+ , Cu 2+ , Ni 2+ , Mn 2+ , Fe 2+ , Co 2+ , Pd 2+ , Ge 2+ , Sn 2+ , Pb 2+ , Yb 2+ and Eu 2+ , preferably Sn 2+ , Pb 2+ , Cu 2+ , Ge 2+ , and Ni 2+ ; Particularly preferably Pb 2+ and Sn 2+ [X] is a halide anion (e.g., Cl - , Br - , and I - ), O 2- , S 2- , Se 2-, and Te 2- a is a number from 1 to 4; b is a number from 1 to 3; and c is a number from 1 to 8.

[0142] Preferably, the formula [A] a [M] b [X] c The compound of formula [A] includes perovskites. a [M] b [X] c Compounds of this type often include metal halide perovskites.

[0143] [M] includes one or more M cations that are metal or metalloid cations. [M] may include two or more different M cations. [M] may include one or more monocations, one or more dications, one or more trications, or one or more tetracations.

[0144] Typically, one or more of the M cations is Ca 2+ , Sr 2+ , Cd 2+ , Cu 2+ , Ni 2+ , Mn 2+ , Fe 2+ , Co 2+ , Pd 2+ , Ge 2+ , Sn 2+ , Pb 2+ , Yb 2+ ,EU 2+ , Bi 3+ , Sb 3+ , Pd 4+ , W 4+ , Re 4+ , Os 4+ , Ir 4+ , Pt 4+ , Sn 4+ , Pb 4+ , Ge 4+ or Te 4+ Preferably, one or more M cations are selected from Cu 2+ , Pb 2+ , Ge 2+ or Sn 2+ Selected from.

[0145] Typically, [M] includes one or more metal or metalloid dications. For example, each M cation is Ca 2+ , Sr 2+ , Cd 2+ , Cu 2+ , Ni 2+ , Mn 2+ , Fe 2+ , Co 2+ , Pd 2+ , Ge 2+ , Sn 2+ , Pb 2+ , Yb 2+ and Eu 2+ , preferably Sn 2+ , Pb 2+ , Cu 2+ , Ge 2+ , and Ni 2+ ; preferably Sn 2+ and Pb 2+ In some embodiments, [M] comprises two different M cations, typically where the cations are selected from Sn 2+ and Pb 2+ , preferably Pb 2+ It is.

[0146] Generally, the one or more A cations are monocations.[A] typically comprises one or more A cations, which can be organic and / or inorganic monocations.Typically, [A] comprises two or more different A cations.Typically, [A] comprises one or more A cations, which comprises at least one organic cation.

[0147] For example, [A] may include at least two A cations, which may be organic and / or inorganic monocations, or at least three A cations, which may be organic and / or inorganic monocations. Thus, the formula [A] a [M] b [X] cThe compound of may be a mixed cation perovskite. [A] may contain at least one A cation that is an organic cation and at least one A cation that is an inorganic cation. [A] may contain at least two A cations that are both organic cations. [A] may contain at least two A cations that are both inorganic cations. In one embodiment, [A] contains two A cations that are both organic cations and an A cation that is an inorganic cation.

[0148] When the A species is an inorganic monocation, A is typically an alkali metal monocation (i.e., a monocation of a metal found in Group 1 of the periodic table), such as Li + , Na + , K + , Rb + , Cs + , e.g. Cs + or Rb + Typically, [A] comprises at least one organic monocation. When the A species is an organic monocation, A is typically an ammonium cation, such as methylammonium, or an iminium cation, such as formamidium.

[0149] Thus, typically each A cation is: an alkali metal cation, e.g., Li+, Na+, K+, Rb+, Cs+; + wherein each of R1, R2, R3, and R4 is independently hydrogen, unsubstituted or substituted C 1-20 Alkyl, and unsubstituted or substituted C 6-12 aryl, and at least one of R1, R2, R3 and R4 is not hydrogen; + wherein each of R5, R6, R7 and R8 is independently hydrogen, unsubstituted or substituted C 1-20 Alkyl, and unsubstituted or substituted C 6-12 Aryl; and C 1-10 Alkylammonium, C 2-10 Alkenylammonium, C 1-10 Alkyliminium, C3-10 Cycloalkylammonium and C 3-10 cycloalkyliminium, each of which is unsubstituted or amino, C 1-6 Alkylamino, imino, C 1-6 Alkylimino, C 1-6 Alkyl, C 2-6 Alkenyl, C 3-6 Cycloalkyl and C 6-12 substituted with one or more substituents selected from aryl; selected from;

[0150] For example, each A cation is Cs + , Rb + , methylammonium [(CH3NH3) + ], ethylammonium [(CH3CH2NH3) + ], propylammonium [(CH3CH2CH2NH3) + ], butylammonium [(CH3CH2CH2CH2NH3) + ], pentylammonium [(CH3CH2CH2CH2CH2NH3) + ], hexylammonium [(CH3CH2CH2CH2CH2CH2NH3) + ], heptylammonium [(CH3CH2CH2CH2CH2CH2CH2NH3) + ], Octylammonium [(CH3CH2CH2CH2CH2CH2CH2CH2NH3) + ], tetramethylammonium [(N(CH3)4) + ], formamidinium [(H2N-C(H)=NH2) + ], 1-aminoethane-1-iminium [(H2N-C(CH3)=NH2) + ] and guanidinium [(H2N-C(NH2)=NH2) + Preferably, each A cation is selected from Cs + , Rb +, methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, heptylammonium, octylammonium, formamidinium and guanidinium.

[0151] [A] usually contains one, two or three A monocations. [A] is methylammonium [(CH3NH3) + ], ethylammonium [(CH3CH2NH3) + ], propylammonium [(CH3CH2CH2NH3)+], dimethylammonium [(CH3)2NH + ], tetramethylammonium [(N(CH3)4) + ], formamidinium [(H2N-C(H)=NH2)+], 1-aminoethane-1-iminium [(H2N-C(CH3)=NH2) + ], guanidinium [(H2N-C(NH2)=NH2) + ], Cs + and Rb + For example, [A] may contain a single cation selected from methylammonium [(CH3NH3) + ].

[0152] Alternatively, [A] may be any of the groups, e.g., Cs + and formamidinium [(H2N-C(H)=NH2) + ], or for example, Cs + and Rb + , or, for example, methylammonium [(CH3NH3) + ] and formamidinium [(H2N-C(H)=NH2) + ], preferably Cs + and formamidinium [(H2N-C(H)=NH2) + ] may contain two cations selected from.

[0153] Alternatively, [A] may be any of the group, e.g., methylammonium [(CH3NH3) +], formamidinium [(H2N-C(H)=NH2) + ] and Cs + The compound may include three cations selected from:

[0154] [X] comprises one or more X anions. Typically, [X] comprises one or more halide anions, i.e., F - , Br - , Cl - and I - Typically, each X anion is a halide. [X] typically contains one, two or three X anions, and these are usually Br - , Cl - and I - Selected from.

[0155] X may contain two or more different X anions. Typically, [X] contains two or more different halide anions. [X] may consist of two X anions, such as Cl and Br, or Br and I, or Cl and I. Thus, the formula [A] a [M] b [X] c Compounds of formula [A] often include mixed halide perovskites. When [A] contains one or more organic cations, the compound of formula [A] a [M] b [X] c The compound may be an organic-inorganic metal halide perovskite.

[0156] Typically, the one or more A cations are monocations, the one or more M cations are dications, and the one or more X anions are one or more halide anions.

[0157] Often, [A] comprises at least two different A cations as described herein, and [X] comprises at least two different X anions as described herein. In some embodiments, [A] comprises at least three different A cations as described herein, and [X] comprises at least two different X anions as described herein.

[0158] Typically, a = 1, b = 1 and c = 3. Thus, in the formula [A] a [M] b [X] c The compound of formula (I) may be a compound of formula [A][M][X]3, where [A], [M] and [X] are as described herein. Typically, the crystalline A / M / X material comprises a perovskite of formula (I): [A][M][X]3(I) wherein: [A] includes one or more A cations that are monocations; [M] includes one or more M cations that are metal or metalloid dications; and [X] includes one or more anions that are halide anions.

[0159] In some embodiments, the perovskite of formula (I) comprises a single A cation, a single M cation and a single X cation, i.e., the perovskite is of formula (IA): AMX3(IA) wherein A, M and X are as defined above. In a preferred embodiment, A is (CHNH) + , (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (H2N-C(H)=NH2) + , (H2N-C(CH3)=NH2) + , (H2N-C(NH2)=NH2) + , Cs + and Rb + M is Pb 2+ or Sn 2+ and X is Br - , Cl - and I - Selected from.

[0160] For example, the crystalline A / M / X material may comprise, or consist essentially of, a perovskite compound of formula (IA) selected from APbI3, APbBr3, APbCl3, ASnI3, ASnBr3 and ASnCl3, where A is a cation as described herein. For example, crystalline A / M / X materials include CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CH3NH3SnI3, CH3NH3SnBr3, CH3NH3SnCl3, CsPbI3, CsPbBr3, CsPbCl3, CsSnI3, CsSnBr3, CsSnCl3, (H2N-C(H)=NH2)PbI3, (H2N-C(H)=NH2)PbBr 3, (H2N-C(H)=NH2)PbCl3, (H2N-C(H)=NH2)SnI3, (H2N-C(H)=NH2)SnBr3 and (H2N-C(H)=NH2)SnCl3, in particular CH3NH3PbI3 or CH3NH3PbBr3, preferably CH3NH3PbI3.

[0161] In one embodiment, the perovskite is a perovskite of formula (IB): [A I x A II 1-x ]MX3(IB) A in the formula I and A II is as defined above for A, where M and X are as defined above, and where x is greater than 0 and less than 1. In a preferred embodiment, A I and A II are (CH3NH3) + , (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (H2N-C(H)=NH2) + , (H2N-C(CH3)=NH2) + , (H2N-C(NH2)=NH2) + , Cs + and Rb +M is Pb 2+ or Sn 2+ and X is Br - , Cl - and I - A I and A II For example, (H2N-C(H)=NH2) + and Cs + or they can be (CH3NH3) + and (H2N-C(H)=NH2) + Alternatively, they can be Cs + and Rb + Preferably, A I and A II are (H2N-C(H)=NH2) + and Cs + It is.

[0162] For example, crystalline A / M / X materials are (Cs x Rb 1-x )PbBr3, (Cs x Rb 1-x )PbCl3, (Cs x Rb 1-x )PbI3, [(CH3NH3) x (H2N-C(H)=NH2) 1-x ]PbCl3, [(CH3NH3) x (H2N-C(H)=NH2) 1-x ]PbBr3,[(CH3NH3) x (H2N-C(H)=NH2) 1-x ]PbI3,[(CH3NH3) x Cs 1-x ]PbCl3, [(CH3NH3) x Cs 1-x ]PbBr3,[(CH3NH3) x Cs 1-x ]PbI3, [(H2N-C(H)=NH2) x Cs 1-x ]PbCl3, [(H2N-C(H)=NH2) x Cs 1-x ]PbBr3, [(H2N-C(H)=NH2) xCs 1-x ]PbI3,[(CH3NH3) x (H2N-C(H)=NH2) 1-x ]SnCl3, [(CH3NH3) x (H2N-C(H)=NH2) 1-x ]SnBr3,[(CH3NH3) x (H2N-C(H)=NH2) 1-x ]SnI3,[(CH3NH3) x Cs 1-x ]SnCl3, [(CH3NH3) x Cs 1-x ]SnBr3,[(CH3NH3) x Cs 1-x ]SnI3, [(H2N-C(H)=NH2) x Cs 1-x ]SnCl3, [(H2N-C(H)=NH2) x Cs 1-x ]SnBr3, and [(H2N-C(H)=NH2) x Cs 1-x ]SnI3, where x is greater than 0 and less than 1, for example, x may be from 0.01 to 0.99, or from 0.05 to 0.95, or from 0.1 to 0.9.

[0163] In one embodiment, the perovskite is a perovskite compound of formula (IC): AM[X I y X II 1-y ]3(IC) where A and M are as defined above, and X I and X II is as defined above for X, and y is greater than 0 and less than 1. In a preferred embodiment, A is (CHNH) + , (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (H2N-C(H)=NH2) + , (H2N-C(CH3)=NH2)+ , (H2N-C(NH2)=NH2) + , Cs + and Rb + M is Pb 2+ or Sn 2+ and X I and X II are Br - , Cl - and I - Selected from.

[0164] For example, crystalline A / M / X materials are APb[Br y I 1-y ]3, APb[Br y Cl 1-y ]3, APb[I y Cl 1-y ]3, ASn[Br y I 1-y ]3, ASn[Br y Cl 1-y ]3, ASn[I y Cl 1-y ]3, preferably APb[Br y I 1-y ]3, where y is greater than 0 and less than 1, and where A is a cation as described herein. y may be from 0.01 to 0.99. For example, y may be from 0.05 to 0.95 or from 0.1 to 0.9.

[0165] For example, crystalline A / M / X materials are CH3NH3Pb[Br y I 1-y ]3, CH3NH3Pb[Br y Cl 1-y ]3, CH3NH3Pb[I y Cl 1-y ]3, CH3NH3Sn[Br y I 1-y ]3, CH3NH3Sn[Br y Cl 1-y ]3, CH3NH3Sn[I y Cl 1-y ]3, CsPb[Br y I 1-y]3, CsPb[Br y Cl 1-y ]3, CsPb[I y Cl 1-y ]3, CsSn[Br y I 1-y ]3, CsSn[Br y Cl 1-y ]3, CsSn[I y Cl 1-y ]3, (H2N-C(H)=NH2)Pb[Br y I 1-y ]3, (H2N-C(H)=NH2)Pb[Br y Cl 1-y ]3, (H2N-C(H)=NH2)Pb[I y Cl 1-y ]3, (H2N-C(H)=NH2)Sn[Br y I 1-y ]3, (H2N-C(H)=NH2)Sn[Br y Cl 1-y ]3, and (H2N-C(H)=NH2)Sn[I y Cl 1-y ]3, where y is greater than 0 and less than 1, for example y may be from 0.01 to 0.99, or from 0.05 to 0.95, or from 0.1 to 0.9.

[0166] In a preferred embodiment, the perovskite is a perovskite of formula (ID): [A I x A II 1-x ]M[X I y X II 1-y ]3(ID) A in the formula I and A II is as defined above for A, M is as defined above, and X I and X II is as defined above for X, and where x and y are both greater than 0 and less than 1. In a preferred embodiment, A I and A IIare ((CH3NH3) + , (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (H2N-C(H)=NH2) + , (H2N-C(CH3)=NH2) + , (H2N-C(NH2)=NH2) + , Cs + and Rb + is selected from, preferably A I and A II are (H2N-C(H)=NH2), respectively. + and Cs + and M is Pb 2+ or Sn 2+ and X I and X II are Br - , Cl - and I - Selected from.

[0167] For example, crystalline A / M / X materials are (Cs x Rb 1-x )Pb(Br y Cl 1-y )3, (Cs x Rb 1-x )Pb(Br y I 1-y )3, and (Cs x Rb 1-x )Pb(Cl y I 1-y )3, [(CH3NH3) x (H2N-C(H)=NH2) 1-x ]Pb[Br y I 1-y ]3, [(CH3NH3) x (H2N-C(H)=NH2) 1-x ]Pb[Br y Cl 1-y ]3, [(CH3NH3) x (H2N-C(H)=NH2) 1-x ]Pb[I y Cl 1-y ]3, [(CH3NH3) x Cs1-x ]Pb[Br y I 1-y ]3、[(CH3NH3) x Cs 1-x ]Pb[Br y Cl 1-y ]3、[(CH3NH3) x Cs 1-x ]Pb[I y Cl 1-y ]3、[(H2N-C(H)=NH2) x Cs 1-x ]Pb[Br y I 1-y ]3、[(H2N-C(H)=NH2) x Cs 1-x ]Pb[Br y Cl 1-y ]3、[(H2N-C(H)=NH2) x Cs 1-x ]Pb[I y Cl 1-y ]3、[(CH3NH3) x (H2N-C(H)=NH2) 1-x ]Sn[Br y I 1-y ]3、[(CH3NH3) x (H2N-C(H)=NH2) 1-x ]Sn[Br y Cl 1-y ]3、[(CH3NH3) x (H2N-C(H)=NH2) 1-x ]Sn[I y Cl 1-y ]3、[(CH3NH3) x Cs 1-x ]Sn[Br y I 1-y ]3、[(CH3NH3) x Cs 1-x ]Sn[Br y Cl 1-y ]3、[(CH3NH3) x Cs 1-x ]Sn[I y Cl 1-y ]3、[(H2N-C(H)=NH2) x Cs 1-x ]Sn[Br y I 1-y]3, [(H2N-C(H)=NH2) x Cs 1-x ]Sn[Br y Cl 1-y ]3, and [(H2N-C(H)=NH2) x Cs 1-x ]Sn[I y Cl 1-y ]3, where x and y are both greater than 0 and less than 1, for example, x and y may both be between 0.01 and 0.99, or between 0.05 and 0.95, or between 0.1 and 0.9. Preferably, the compound of formula (ID) is selected from [(H2N-C(H)=NH2) x Cs 1-x ]Pb[Br y I 1-y ]3.

[0168] In one embodiment, the perovskite is of formula (IE): A[M I z M II 1-z ]X3(IE) M in the formula I and M. II is as defined above for M, A and X are as defined above, and z is greater than 0 and less than 1. In a preferred embodiment, A is (CHNH) + , (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (H2N-C(H)=NH2) + , (H2N-C(CH3)=NH2) + , (H2N-C(NH2)=NH2) + , Cs + and Rb + Selected from;M I is Pb 2+ And M II is Sn 2+ and X is Br - , Cl - and I -Selected from.

[0169] For example, crystalline A / M / X materials are CH3NH3[Pb z Sn 1-z ]Cl3, CH3NH3[Pb z Sn 1-z ]Br3, CH3NH3[Pb z Sn 1-z ]I3, Cs[Pb z Sn 1-z ]Cl3, Cs[Pb z Sn 1-z ]Br3, Cs[Pb z Sn 1-z ]I3, (H2N-C(H)=NH2)[Pb z Sn 1-z ]Cl3, (H2N-C(H)=NH2)[Pb z Sn 1-z ]Br3, and (H2N-C(H)=NH2)[Pb z Sn 1-z ]I3, where z is greater than 0 and less than 1, for example z may be from 0.01 to 0.99 or from 0.05 to 0.95 or from 0.1 to 0.9.

[0170] In one embodiment, the perovskite is a perovskite of formula (IF): [A I x A II 1-x ][M I z M II 1-z ]X3(IF) A in the formula I and A II is as defined above for A, and M I and M. II is as defined above for M, and X is as defined above, and wherein x and z are both greater than 0 and less than 1. In a preferred embodiment, A I and A II are (CH3NH3), respectively. +, (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (H2N-C(H)=NH2) + , (H2N-C(CH3)=NH2) + , (H2N-C(NH2)=NH2) + , Cs + and Rb + Selected from;M I is Pb 2+ And M II is Sn 2+ and X is Br - , Cl - and I - A I and A II For example, (H2N-C(H)=NH2) + and Cs + or (CH3NH3), respectively. + and (H2N-C(H)=NH2) + Alternatively, they can be Cs + and Rb + It could be.

[0171] For example, crystalline A / M / X materials are [(CH3NH3) x (H2N-C(H)=NH2) 1-x ][Pb z Sn 1-z ]Cl3, [(CH3NH3) x (H2N-C(H)=NH2) 1-x ][Pb z Sn 1-z ]Br3,[(CH3NH3) x (H2N-C(H)=NH2) 1-x ][Pb z Sn 1-z ]I3, [(CH3NH3) x Cs 1-x ][Pb z Sn 1-z ]Cl3, [(CH3NH3) x Cs 1-x ][Pb z Sn 1-z]Br3,[(CH3NH3) x Cs 1-x ][Pb z Sn 1-z ]I3, [(H2N-C(H)=NH2) x Cs 1-x ][Pb z Sn 1-z ]Cl3, [(H2N-C(H)=NH2) x Cs 1-x ][Pb z Sn 1-z ]Br3, [(H2N-C(H)=NH2) x Cs 1-x ][Pb z Sn 1-z ]I3, where x and z are both greater than 0 and less than 1, for example, x and z may each be from 0.01 to 0.99 or from 0.05 to 0.95 or from 0.1 to 0.9. Preferably, the compound of formula (IF) is selected from [(CH3NH3) x Cs 1-x ][Pb z Sn 1-z ]I3 or [(H2N-C(H)=NH2) x Cs 1-x ][Pb z Sn 1-z ]I3, where x and z can each be 0.01 to 0.99 or 0.05 to 0.95 or 0.1 to 0.9, typically where x is 0.95 to 0.70 and z is 0.25 to 0.75.

[0172] In one embodiment, the perovskite is a perovskite compound of formula (IG): A[M I z M II 1-z ][X I y X II 1-y ]3(IG) In the formula, A is as defined above, and M I and M. II is as defined above for M, andI and X II is as defined above for X, and where y and z are both greater than 0 and less than 1. In a preferred embodiment, A is (CHNH) + , (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (H2N-C(H)=NH2) + , (H2N-C(CH3)=NH2) + , (H2N-C(NH2)=NH2) + , Cs + and Rb + Selected from;M I is Pb 2+ And M II is Sn 2+ and X I and X II are Br - , Cl - and I - Selected from.

[0173] For example, crystalline A / M / X materials are z Sn 1-z ][Br y I 1-y ]3, A[Pb z Sn 1-z ][Br y Cl 1-y ]3, A[Pb z Sn 1-z ][I y Cl 1-y

[0033] 3, where y and z are both greater than 0 and less than 1, and where A is a cation as described herein. Y and z can each be from 0.01 to 0.99. For example, y and z can each be from 0.05 to 0.95 or from 0.1 to 0.9.

[0174] For example, crystalline A / M / X materials are CH3NH3[Pb z Sn 1-z ][Br yI 1-y ]3, CH3NH3[Pb z Sn 1-z ][Br y Cl 1-y ]3, CH3NH3[Pb z Sn 1-z ][I y Cl 1-y ]3, Cs[Pb z Sn 1-z ][Br y I 1-y ]3, Cs[Pb z Sn 1-z ][Br y Cl 1-y ]3, Cs[Pb z Sn 1-z ][I y Cl 1-y ]3, (H2N-C(H)=NH2)[Pb z Sn 1-z ][Br y I 1-y ]3, (H2N-C(H)=NH2)[Pb z Sn 1-z ][Br y Cl 1-y ]3, and (H2N-C(H)=NH2)[Pb z Sn 1-z ][I y Cl 1-y 3, wherein y and z are both greater than 0 and less than 1, for example, y and z may each be from 0.01 to 0.99, or from 0.05 to 0.95, or from 0.1 to 0.9.

[0175] In a preferred embodiment, the perovskite is a perovskite of formula (IH): [A I x A II 1-x ][M I z M II 1-z ][X I y X II 1-y ]3(IH) A in the formulaI and A II is as defined above for A, and M I and M. II is as defined above for M, and X I and X II is as defined above for X, and where x, y and z are each greater than 0 and less than 1. In a preferred embodiment, A I and A II are respectively ((CH3NH3) + , (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (H2N-C(H)=NH2) + , (H2N-C(CH3)=NH2) + , (H2N-C(NH2)=NH2) + , Cs + and Rb + Selected from;M I is Pb 2+ And M II is Sn 2+ and X I and X II are Br - , Cl - and I - Selected from.

[0176] For example, crystalline A / M / X materials are [(CH3NH3) x (H2N-C(H)=NH2) 1-x ][Pb z Sn 1-z ][Br y I 1-y ]3, [(CH3NH3) x (H2N-C(H)=NH2) 1-x ][Pb z Sn 1-z ][Br y Cl 1-y ]3, (CH3NH3) x (H2N-C(H)=NH2) 1-x ][Pb z Sn 1-z ][I yCl 1-y ]3, [(CH3NH3) x Cs 1-x ][Pb z Sn 1-z ][Br y I 1-y ]3, [(CH3NH3) x Cs 1-x ][Pb z Sn 1-z ][Br y Cl 1-y ]3, [(CH3NH3) x Cs 1-x ][Pb z Sn 1-z ][I y Cl 1-y ]3, [(H2N-C(H)=NH2) x Cs 1-x ][Pb z Sn 1-z ][Br y I 1-y ]3, [(H2N-C(H)=NH2) x Cs 1-x ][Pb z Sn 1-z ][Br y Cl 1-y ]3, and [(H2N-C(H)=NH2) x Cs 1-x ][Pb z Sn 1-z ][I y Cl 1-y

[0033] wherein x, y and z are each greater than 0 and less than 1, for example, x, y and z may each be 0.01 to 0.99, or 0.05 to 0.95, or 0.1 to 0.9.

[0177] In one embodiment, a = 2, b = 1 and c = 4. In that embodiment, the crystalline A / M / X material comprises a compound of formula (II) (a "2D layered perovskite"): [A]2[M][X]4(II) wherein: [A] comprises one or more A cations which are monocations; [M] comprises one or more M cations which are metal or metalloid dications; and [X] comprises one or more X anions which are halide anions. In this embodiment, the A and M cations, and the X anions are as defined above.

[0178] The Ruddersden-Popper phase refers to a perovskite having a mixture of layered 3D components. Typically, the layered 2D components may be of formula (II). Such perovskites have the crystal structure A n-1 A'2M n X 3n+1 where A and A' are different A cations as described herein, M is one or more M cations as described herein, X is one or more X anions as described herein, and n is an integer from 1 to 8, or from 2 to 6. The term "mixed 2D and 3D" perovskites refers to perovskites that are made up of AMX3 and A n-1 A'2M n X 3n+1 It is used to refer to a perovskite film in which both regions or domains of the perovskite phase are present, where A, M and X are all as defined herein.

[0179] In another embodiment, a = 2, b = 1 and c = 6. In that embodiment, the crystalline A / M / X material may then comprise a hexahalometalate of formula (III): [A]2[M][X]6(III) where: [A] includes one or more A cations that are monocations; [M] includes one or more M cations that are metal or metalloid tetracations; and [X] includes one or more X anions that are halide anions.

[0180] The hexahalometallate of formula (III) may be a mixed monocation hexahalometallate in a preferred embodiment. In a mixed monocation hexahalometallate, [A] contains at least two A cations that are monocations; [M] contains at least one M cation that is a metal or metalloid tetracation (and typically, [M] contains a single M cation that is a metal or metalloid tetracation); and [X] contains at least one X anion that is a halide anion (and typically, [X] contains a single halide anion or two types of halide anions). In a mixed metal hexahalometallate, [A] contains at least one monocation (and typically, [A] is a single monocation or two types of monocations); [M] contains at least two metal or metalloid tetracations (e.g., Ge). 4+ and Sn 4+ and [X] comprises at least one halide anion (and typically, [X] is a single halide anion or two types of halide anions). In mixed halide hexahalometalates, [A] comprises at least one monocation (and typically, [A] is a single monocation or two types of monocations); [M] comprises at least one metal or metalloid tetracation (and typically, [M] is a single metal tetracation); and [X] comprises at least two halide anions, e.g., Br - and Cl - or Br - and I - Includes.

[0181] [A] may include at least one A monocation selected from any suitable monocation, such as those described above for perovskites. In the case of hexahalometalates, each A cation is typically Li + , Na + , K + , Rb + , Cs + , NH4 +and monovalent organic cations. Monovalent organic cations are organic cations that have a single positive charge, and they may have, for example, a molecular weight of 500 g / mol or less. For example, [A] is Li + , Na + , K + , Rb + , Cs + , NH4 + and a monovalent organic cation. [A] is preferably Rb + , Cs + , NH4 + and at least one A cation which is a monocation selected from monovalent organic cations. For example, [A] is Li + , Na + , K + , Rb + , Cs + and NH4 + In another embodiment, [A] can be at least one monovalent organic A cation. For example, [A] can be a single monovalent organic A cation. In one embodiment, [A] is (CHNH) + In another embodiment, [A] is (H2N-C(H)=NH2) + It is.

[0182] Preferably, [A] contains two or more types of A cations. [A] may be a single A monocation, or in fact two A monocations, each of which is K + , Rb + , Cs + , NH4 + , (CH3NH3) + , (CH3CH2NH3) + , (CH3CH2CH2NH3) + , (N(CH3)4) + , (N(CH2CH3)4) + , (N(CH2CH2CH3)4) + , (H2N-C(H)=NH2) + and (H2N-C(CH3)=NH2) + are selected independently.

[0183] [M] may include one or more M cations selected from suitable metal or metalloid tetracations. Metals include elements in groups 3-12 of the Periodic Table of the Elements, as well as Ga, In, Tl, Sn, Pb, Bi, and Po. Metalloids include Si, Ge, As, Sb, and Te. For example, [M] may include Ti 4+ , V 4+ , Mn 4+ , Fe 4+ , Co 4+ , Zr 4+ , Nb 4+ , Mo 4+ , Ru 4+ , Rh 4+ , Pd 4+ , Hf 4+ , Ta 4+ , W 4+ , Re 4+ , Os 4+ , Ir 4+ , Pt 4+ , Sn 4+ , Pb 4+ , Po 4+ , Si 4+ , Ge 4+ , and Te 4+ Typically, [M] is selected from the group consisting of Pd 4+ , W 4+ , Re 4+ , Os 4+ , Ir 4+ , Pt 4+ , Sn 4+ , Pb 4+ , Ge 4+ , and Te 4+ For example, [M] is selected from Pd 4+ , W 4+ , Re 4+ , Os 4+ , Ir 4+ , Pt 4+ , Sn 4+ , Pb 4+ , Ge 4+ , and Te 4+ The cation may be a single metal or metalloid tetracation selected from:

[0184] Typically, [M] is Sn 4+ , Te 4+ , Ge 4+ and Re 4+ In one embodiment, [M] is selected from the group consisting of Pb 4+ , Sn 4+ , Te 4+ , Ge 4+ and Re 4+ At least one M cation is a metal or metalloid tetracation selected from the group consisting of Pb 4+ , Sn 4+ , Te 4+ and Ge 4+ Preferably, [M] is at least one metal or semimetal tetracation selected from Sn 4+ , Te 4+ , and Ge 4+ As discussed above, the hexahalometallate compound may be a mixed-metal or single-metal hexahalometallate. Preferably, the hexahalometallate compound is a single-metal hexahalometallate compound. More preferably, [M] is selected from the group consisting of Sn 4+ , Te 4+ , and Ge 4+ For example, [M] is Te 4+ For example, [M] can be a single metal or metalloid tetracation, 4+ Most preferably, [M] is a single metal or semimetal tetracation, 4+ is a single metal or metalloid tetracation where

[0185] [X] may include at least one X anion that is a halide anion. Thus, [X] may include F - , Cl - , Br - and I -Typically, [X] is selected from the group consisting of Cl - , Br - and I - The hexahalometallate compound may be a mixed-halide hexahalometallate or a single-halide hexahalometallate. When the hexahalometallate is a mixed halide, [X] is selected from the group consisting of F - , Cl - , Br - and I - Typically, in the mixed-halide compounds, [X] is selected from F - , Cl - , Br - and I - It contains two halide anions selected from:

[0186] In some embodiments, [A] is a single monocation and [M] is a single metal or metalloid tetracation. Thus, the crystalline A / M / X material can include, for example, a hexahalometallate compound of formula (IIIA): A2M[X]6(IIIA) where A is a monocation; M is a metal or metalloid tetracation; and [X] is at least one halide anion. [X] is F - , Cl - , Br - and I - and preferably Cl - , Br - and I - In formula (IIIA), [X] is preferably one, two or three halide anions selected from Cl. - , Br - and I - and wherein the anions are one or two halide anions selected from the group consisting of:

[0187] The crystalline A / M / X material may, for example, comprise or consist essentially of a hexahalometallate compound of formula (IIIB): A2MX 6-y X' y (IIIB) where: A is a monocation (i.e., a second cation); M is a metal or metalloid tetracation (i.e., a first cation); X and X' are each independently (different) halide anions (i.e., two second anions); and y is 0 to 6. When y is 0 or 6, the hexahalometallate compound is a single-halide compound. When y is 0.01 to 5.99, the compound is a mixed-halide hexahalometallate compound. When the compound is a mixed-halide compound, y can be 0.05 to 5.95. For example, y can be 1.00 to 5.00.

[0188] The hexahalometalate compound is, for example, A2SnF 6-y Cl y , A2SnF 6-y Br y , A2SnF 6-y I y , A2SnCl 6-y Br y , A2SnCl 6-y I y , A2SnBr 6-y I y , A2TeF 6-y Cl y , A2TeF 6-y Br y , A2TeF 6-y I y , A2TeCl 6-y Br y , A2TeCl 6-y I y , A2TeBr 6-y I y , A2GeF 6-y Cl y , A2GeF 6-y Br y , A2GeF 6-y I y , A2GeCl 6-y Br y , A2GeCl 6-y I y , A2GeBr 6-y I y, A2ReF 6-y Cl y , A2ReF 6-y Br y , A2ReF 6-y I y , A2ReCl 6-y Br y , A2ReCl 6-y I y or A2ReBr 6-y I y where A is K + , Rb + , Cs + , (R 1 NH3) + , (NR 2 4) + , or (H2N-C(R 1 )=NH2) + where R 1 is H, substituted or unsubstituted C 1-20 is an alkyl group or a substituted or unsubstituted aryl group, and R 2 is substituted or unsubstituted C 1-10 is an alkyl group; and y is 0 to 6. Optionally, y is 0.01 to 5.99. When the hexahalometallate compound is a mixed-halide compound, y is typically 1.00 to 5.00. A can be as defined above. For example, A can be Cs + , NH4 + , (CH3NH3) + , (CH3CH2NH3) + , (N(CH3)4) + , (N(CH2CH3)4) + , (H2N-C(H)=NH2) + or (H2N-C(CH3)=NH2) + , e.g., Cs + , NH4 + , or (CH3NH3) + It could be.

[0189] The hexahalometalate compound is typically A2SnF 6-y Cl y , A2SnF 6-y Br y , A2SnF 6-yI y , A2SnCl 6-y Br y , A2SnCl 6-y I y , or A2SnBr 6-y I y where A is K + , Rb + , Cs + , (R 1 NH3) + , (NR 2 4) + , or (H2N-C(R 1 )=NH2) + or A is as defined herein, where R 1 is H, substituted or unsubstituted C 1-20 an alkyl group or a substituted or unsubstituted aryl group, or R 2 is substituted or unsubstituted C 1-10 is an alkyl group; and y is 0-6.

[0190] In another embodiment, the hexahalometalate compound is A2GeF 6-y Cl y , A2GeF 6-y Br y , A2GeF 6-y I y , A2GeCl 6-y Br y , A2GeCl 6-y I y , or A2GeBr 6-y I y where: A is K + , Rb + , Cs + , (R 1 NH3) + , (NR 2 4) + , or (H2N-C(R 1 )=NH2) + or A is as defined herein, where R 1 is H, substituted or unsubstituted C 1-20 is an alkyl group or a substituted or unsubstituted aryl group, and R 2 is substituted or unsubstituted C1-10 is an alkyl group; and y is 0-6.

[0191] The hexahalometalate compound is, for example, A2TeF 6-y Cl y , A2TeF 6-y Br y , A2TeF 6-y I y , A2TeCl 6-y Br y , A2TeCl 6-y I y , or A2TeBr 6-y I y where A is K + , Rb + , Cs + , (R 1 NH3) + , (NR 2 4) + , or (H2N-C(R 1 )=NH2) + or A is as defined herein, where R 1 is H, substituted or unsubstituted C 1-20 is an alkyl group or a substituted or unsubstituted aryl group, and R 2 is substituted or unsubstituted C 1-10 is an alkyl group; and y is 0 to 6, or y is as defined herein.

[0192] Often, y is between 1.50 and 2.50. For example, y can be between 1.80 and 2.20. This can occur when the compound is prepared using 2 equivalents of AX' and 1 equivalent of MX4, as discussed below.

[0193] In some embodiments, all of the ions are a single anion or cation. Thus, the crystalline A / M / X material can comprise or consist essentially of a hexahalometallate compound of formula (IIIC): A2MX6(IIIC) wherein: A is a monocation; M is a metal or metalloid tetracation; and X is a halide anion. A, M and X may be as defined herein.

[0194] The hexahalometalate compound can be A2SnF6, A2SnCl6, A2SnBr6, A2SnI6, A2TeF6, A2TeCl6, A2TeBr6, A2TeI6, A2GeF6, A2GeCl6, A2GeBr6, A2GeI6, A2ReF6, A2ReCl6, A2ReBr6, or A2ReI6, where A is K. + , Rb + , Cs + , (R 1 NH3) + , (NR 2 4) + , or (H2N-C(R 1 )=NH2) + where R 1 is H, substituted or unsubstituted C 1-20 is an alkyl group or a substituted or unsubstituted aryl group, and R 2 is substituted or unsubstituted C 1-10 A is an alkyl group. A can be as defined herein. Preferably, the hexahalometallate compound is Cs2SnI6, Cs2SnBr6, Cs2SnBr 6-y I y , Cs2SnCl 6-y I y , Cs2SnCl 6-y Br y , (CH3NH3)2SnI6, (CH3NH3)2SnBr6, (CH3NH3)2SnBr 6-y I y , (CH3NH3)2SnCl 6-y I y , (CH3NH3)2SnCl 6-y Br y , (H2N-C(H)=NH2)2SnI6, (H2N-C(H)=NH2)2SnBr6, (H2N-C(H)=NH2)2SnBr 6-y I y , (H2N-C(H)=NH2)2SnCl 6-y I yor (H2N-C(H)=NH2)2SnCl 6-y Br y where y is 0.01 to 5.99. For example, the hexahalometalate compound can be (CH3NH3)2SnI6, (CH3NH3)2SnBr6, (CH3NH3)2SnCl6, (H2N-C(H)=NH2)2SnI6, (H2N-C(H)=NH2)2SnBr6, or (H2N-C(H)=NH2)2SnCl6. The hexahalometalate compound can be Cs2SnI6, Cs2SnBr6, Cs2SnCl 6-y Br y , (CH3NH3)2SnI6, (CH3NH3)2SnBr6, or (H2N-C(H)=NH2)2SnI6.

[0195] The crystalline A / M / X material may include a bismuth or antimony halogenometallate. For example, the crystalline A / M / X material may include a halogenometallate compound that includes: (i) one or more monocations ([A]) or one or more dications ([B]); (ii) one or more metal or metalloid trications ([M]); and (iii) one or more halide anions ([X]). The compound may be of formula BBiX5, B2BiX7, or B3BiX9, where B is (H3NCH2NH3). 2+ , (H3N(CH2)2NH3) 2+ , (H3N(CH2)3NH3) 2+ , (H3N(CH2)4NH3) 2+ , (H3N(CH2)5NH3) 2+ , (H3N(CH2)6NH3) 2+ , (H3N(CH2)7NH3) 2+ , (H3N(CH2)8NH3) 2+ or (H3N-C6H4-NH3) 2+ and X is I - , Br - or Cl - , preferably I - It is.

[0196] In yet further embodiments, the crystalline A / M / X material may be a double perovskite. Such compounds are defined in WO 2017 / 037448, the entire contents of which are incorporated herein by reference. Typically, the compound is a double perovskite compound of formula (IV): [A]2[B + ][B 3+ ][X]6(IV); where: [A] comprises one or more A cations, which are monocations as defined herein; [B + ] and [B 3+ ] is equivalent to [M], where M contains one or more M cations that are monocations and one or more M cations that are tricationic; and [X] contains one or more X anions that are halide anions.

[0197] [B + The one or more M cations which are monocations in the formula (I) are typically selected from metal and semimetal monocations. Preferably, the one or more M cations which are monocations are Li + , Na + , K + , Rb + , Cs + , Cu + , Ag + , Au + and Hg + More preferably, the one or more M cations that are monocations are selected from Cu + , Ag + and Au + Most preferably, the one or more M cations that are monocations are selected from Ag + and Au + For example, [B + ] is Ag + or [B + ] is Au + The cation can be one monocation,

[0198] [B 3+The one or more M cations in the trication are typically selected from metal and metalloid trications. Preferably, the one or more M cations in the trication are selected from Bi 3+ , Sb 3+ , Cr 3+ , Fe 3+ , Co 3+ , Ga 3+ , As 3+ , Ru 3+ , Rh 3+ , In 3+ , Ir 3+ and Au 3+ More preferably, the one or more M cations that are trications are selected from Bi 3+ and Sb 3+ For example, [B 3+ ] is Bi 3+ or [B 3+ ] is Sb 3+ Bismuth has relatively low toxicity compared to heavy metals such as lead. In some embodiments, one or more M cations ([B + ]) is Cu + , Ag + and Au + and one or more M cations ([B 3+ ]) is Bi 3+ and Sb 3+ Selected from.

[0199] An exemplary double perovskite is Cs2BiAgBr6.

[0200] Typically, when the compound is a double perovskite, it is a compound of formula (IVa): A2B + B 3+ [X]6(IVa); where: A cation is as defined herein; B + is a M cation, which is a monocation as defined herein; B 3+is an M cation that is a trication as defined herein; and [X] includes one or more X anions that are halide anions, for example, two or more halide anions, preferably a single halide anion.

[0201] In yet another embodiment, the compound may be a layered double perovskite compound of formula (V): [A]4[B + ][B 3+ ][X]8(V); In the formula: [A], [B + ], [B 3+ [X] are as defined above. In some embodiments, the layered double perovskite compound is a double perovskite compound of formula (Va): A4B + B 3+ [X]8(Va); where: A cation is as defined herein; B + is a M cation, which is a monocation as defined herein; B 3+ is an M cation that is a trication as defined herein; and [X] includes one or more X anions that are halide anions, for example, two or more halide anions, preferably a single halide anion or two or more halide anions.

[0202] In yet another embodiment, the compound can be a compound of formula (VI): [A]4[M][X]6(VI); wherein: [A], [M] and [X] are as defined above (e.g., for compounds of formula (I) or (II)). Preferably, however, the compound is not a compound of formula (VI). When the compound is a compound of formula (VI), it is preferably a compound of formula (VIA): [A I A II ]4[M][X]6(VIA); That is, [A] may be a compound containing two types of A monocations. In another preferred embodiment, the compound of formula (VI) is a compound of formula (VIB): [A]4[M][X I X II ]6(VIB); That is, the compound of formula (VI) may be one in which [X] comprises two types of X anions. In yet another preferred embodiment, the compound of formula (VI) may be one of formula (VIC): [A I A II ]4[M][X I X II ]6(VIC); That is, a compound of formula (VI) in which [A] comprises two types of A monocations and [X] comprises two types of X anions. In formulas (VIa), (VIb) and (VIc), each of [A], [M] and [X] is as defined above (e.g., with respect to a compound of formula (I) or (II)).

[0203] In another embodiment, a = 1, b = 1 and c = 4. In that embodiment, the crystalline A / M / X material may then comprise a compound of formula (VII): [A][M][X]4(VII) Wherein: [A] comprises one or more A cations which are monocations; [M] comprises one or more M cations which are metal or metalloid trications; and [X] comprises one or more X anions which are halide anions. The A monocations and M trications are as defined herein. An exemplary compound of formula (VII) is AgBiI4.

[0204] Typically, the first photoactive material comprises at least one first A / M / X material described herein, and the second photoactive material comprises at least one second A / M / X material described herein. Typically, the first photoactive material consists essentially of or consists of at least one first A / M / X material described herein, and the second photoactive material consists essentially of or consists of at least one second A / M / X material described herein. Preferably, the at least one first and second A / M / X materials are different. For example, the first A / M / X material can be a compound of formula (I), (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (II), (III), (IV), (V), (VI), and (VII) described above, and the second A / M / X material can be a different compound of formula (I), (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (II), (III), (IV), (V), (VI), and (VII) described above.

[0205] Typically, the first photoactive material comprises a first A / M / X material, where [X] comprises two or more X anions, where each X anion is a halide, preferably where [X] comprises Br and I. [A] in the first A / M / X material may comprise two or more A cations, typically where one of the A cations is an organic cation. For example, [A] in the first A / M / X material may comprise Cs + and formamidinium.

[0206] In one embodiment, the first A / M / X material is a compound of formula (IC) described herein, e.g., APb[Br y I 1-y ]3, where y is greater than 0 and less than 1, and where A is a cation as described herein. Y can be from 0.01 to 0.99. Y can be from 0.05 to 0.95 or from 0.1 to 0.9. Typically, A is Cs + and therefore the compound of formula (IC) is CsPb[Br y I 1-y ]3.

[0207] In another embodiment, the first A / M / X material is a compound of formula (ID) described herein, e.g., a compound of formula [(H2N-C(H)=NH2) x Cs 1-x ]Pb[Br y I 1-y ]3, where x and y are both greater than 0 and less than 1, for example, x and y can both be 0.01 to 0.99 or 0.05 to 0.95 or 0.1 to 0.9.

[0208] In another embodiment, the first A / M / X material comprises a compound of formula (II). For example, the first A / M / X material can comprise a mixed 2D and 3D perovskite described herein.

[0209] Typically, the second photoactive material comprises a second A / M / X material, where [M] in the second A / M / X material comprises two or more M cations. Preferably, [M] is Pb 2+ and Sn 2+ Includes.

[0210] For example, in one embodiment, the second A / M / X material is a compound of formula (IE) described herein, e.g., CH3NH3[Pb z Sn 1-z ]Cl3, CH3NH3[Pb z Sn 1-z ]Br3, CH3NH3[Pb z Sn 1-z ]I3, Cs[Pb z Sn 1-z ]Cl3, Cs[Pb z Sn 1-z ]Br3, Cs[Pb z Sn 1-z ]I3, (H2N-C(H)=NH2)[Pb z Sn 1-z ]Cl3, (H2N-C(H)=NH2)[Pb z Sn 1-z ]Br3, and (H2N-C(H)=NH2)[Pb z Sn 1-z]I3, where z is greater than 0 and less than 1, for example, z can be 0.01 to 0.99 or 0.05 to 0.95 or 0.1 to 0.9.

[0211] In another embodiment, the second A / M / X material is a compound of formula (IF) described herein, for example, a compound of formula [(CH3NH3) x Cs 1-x ][Pb z Sn 1-z ]I3, where x and z are both greater than 0 and less than 1, for example, x and z can each be 0.01 to 0.99, or 0.05 to 0.95, or 0.1 to 0.9.

[0212] In another embodiment, the second A / M / X material is [(H2N-C(H)=NH2) x Cs 1-x ][Pb z Sn 1-z ]I3, where x and z can each be 0.01 to 0.99 or 0.05 to 0.95 or 0.1 to 0.9, typically where x is 0.95 to 0.70 and z is 0.25 to 0.75.

[0213] In one embodiment, the first photoactive material comprises a first A / M / X material described herein, and the second photoactive material comprises a compound comprising a chalcogenide anion, typically a metal chalcogenide comprising at least one metal and at least one chalcogenide anion. For example, the first photoactive material can be a compound of formula (ID) and the second photoactive material can be copper indium gallium selenide (CIGS) or copper indium sulfide (CIS). In one embodiment, the first photoactive material comprises a compound of formula [(H2N-C(H)=NH2) x Cs 1-x ]Pb[Br y I 1-y ]3, where x and y are both greater than 0 and less than 1, e.g., x and y can both be 0.01 to 0.99 or 0.05 to 0.95 or 0.1 to 0.9, e.g., [(H2N-C(H)=NH2)0.8 Cs 0.2 ]Pb[Br 0.1 I 0.9 ]3, and the second photoactive material can be copper indium gallium selenide (CIGS) or copper indium sulfide (CIS).

[0214] Device Structure Typically, in multijunction devices of the invention, each photoactive region further comprises one or more charge transport layers. Typically, each photoactive region comprises at least two charge transport layers.

[0215] The charge transport layer can be an electron transport (n-type) layer or a hole transport (p-type) layer. Typically, each photoactive region includes an electron transport (n-type) layer and a hole transport (p-type) layer.

[0216] Typically, each photoactive region includes a layer of photoactive material disposed between an electron-transporting (n-type) layer and a hole-transporting (p-type) layer. Thus, each photoactive region may include the following layers, in the following order: - hole transport (p-type) layer; - a layer of a photoactive material as described herein; - Electron transport (n-type) layer.

[0217] Thus, in one embodiment, a multijunction device may comprise the following layers in the following order: - hole transport (p-type) layer; - a layer of a first photoactive material as described herein; - Electron transport (n-type) layer; - a charge recombination layer as described herein; - hole transport (p-type) layer; - a layer of a second photoactive material as described herein; - Electron transport (n-type) layer.

[0218] The n-type layer may comprise, consist essentially of, or consist of an electron transporting (n-type) material. Examples of electron transporting (n-type) materials are known to those skilled in the art. Suitable n-type materials may be organic or inorganic. Suitable inorganic n-type materials may be selected from metal oxides, metal sulfides, metal selenides, metal tellurides, perovskites, amorphous Si, n-type Group IV semiconductors, n-type Group III-V semiconductors, n-type Group II-VI semiconductors, n-type Group I-VII semiconductors, n-type Group IV-VI semiconductors, n-type Group V-VI semiconductors, and n-type Group II-V semiconductors, any of which may be doped or undoped. More typically, the n-type material is selected from metal oxides, metal sulfides, metal selenides, and metal tellurides.

[0219] Thus, the n-type layer may comprise an inorganic material selected from oxides of titanium, tin, zinc, niobium, tantalum, tungsten, indium, gallium, neodymium, palladium, or cadmium, or oxides of a mixture of two or more of said metals. For example, the n-type layer may comprise TiO2, SnO2, ZnO, Nb2O5, Ta2O5, WO3, W2O5, In2O3, Ga2O3, Nd2O3, PbO, or CdO. Other suitable n-type materials that may be employed include sulfides of cadmium, tin, copper, or zinc, including sulfides of a mixture of two or more of said metals. For example, the sulfides may be FeS2, CdS, ZnS, SnS, BiS, SbS, or Cu2ZnSnS4.

[0220] The n-type layer may, for example, comprise a selenide of cadmium, zinc, indium, or gallium, or a mixture of two or more of the metals; or a telluride of cadmium, zinc, cadmium, or tin, or a mixture of two or more of the metals. For example, the selenide may be Cu(In,Ga)Se2. Typically, the telluride is a telluride of cadmium, zinc, cadmium, or tin. For example, the telluride may be CdTe.

[0221] The n-type layer may comprise an inorganic material selected from, for example, oxides of titanium (e.g., TiO2), tin (e.g., SnO2), zinc (e.g., ZnO), niobium, tantalum, tungsten, indium, gallium, neodymium, palladium, cadmium, or a mixture of two or more of said metals; sulfides of cadmium, tin, copper, zinc, or a mixture of two or more of said metals; selenides of cadmium, zinc, indium, gallium, or a mixture of two or more of said metals; or tellurides of cadmium, zinc, cadmium, or tin, or a mixture of two or more of said metals.

[0222] Examples of other semiconductors that may be suitable n-type materials include, for example, when they are n-doped, Group IV elemental or compound semiconductors; amorphous Si; Group III-V semiconductors (e.g., gallium arsenide); Group II-VI semiconductors (e.g., cadmium selenide); Group I-VII semiconductors (e.g., cuprous chloride); Group IV-VI semiconductors (e.g., lead selenide); Group V-VI semiconductors (e.g., bismuth telluride); and Group II-V semiconductors (e.g., cadmium arsenide).

[0223] Other n-type materials may also be employed, including organic and polymeric electron transport materials, and electrolytes. Suitable examples include fullerenes or fullerene derivatives (e.g., C 60 , C 70 , Phenyl-C 61 -Butyric acid methyl ester (PCBM), PC 71 BM (i.e., phenyl C 71 Butyric acid methyl ester, bis[C 60 ]BM (i.e., bis-C 60 butyric acid methyl ester), and 1',1'',4',4''-tetrahydro-di[1,4]methanonaphthaleno[1,2:2',3',56,60:2'',3''][5,6]fullerene-C 60(ICBA)), organic electron transport materials containing perylene or its derivatives, poly{[N,N0-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,50-(2,20-bithiophene)} (P(NDI2OD-T2)), bathocuproine (BCP) or C 60 / BCP, including but not limited to:

[0224] Typically, the n-type material is phenyl-C61-butyric acid methyl ester (PCBM) or C 60 / BCP.

[0225] In some embodiments, the n-type layer may include two sub-layers, each of which includes an n-type material. For example, the n-type layer may include a first sub-layer that includes an organic n-type material, preferably PCBM, and a second sub-layer that includes an inorganic n-type material, preferably SnO2.

[0226] A p-type layer may comprise, consist essentially of, or consist of a hole-transporting (p-type) material. Examples of hole-transporting (p-type) materials are known to those skilled in the art. A p-type material may be a single p-type compound or elemental material, or a mixture of two or more p-type compounds or elemental materials, which may be undoped or doped with one or more dopant elements.

[0227] The p-type material may include inorganic or organic p-type materials. For example, the p-type material may be an organic p-type material.

[0228] Suitable p-type materials can be selected from polymers or molecular hole transporters, such as spiro-OMeTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene), P3HT (poly(3-hexylthiophene)), PCPDTBT (poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl]]), PVK (poly(N-vinylcarbazole)), HTM-TFSI (1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), Li-TFSI (lithium bis(trifluoromethanesulfonyl)imide), spiro-OMETAD + -Bis(trifluoromethanesulfonyl)imide -(spiro(TFSI)2), tBP (tert-butylpyridine), m-MTDATA (4,4',4''-tris(methylphenylphenylamino)triphenylamine), MeOTPD (N,N,N',N'-tetrakis(4-methoxyphenyl)-benzidine), BP2T (5,5'-di(biphenyl-4-yl)-2,2'-bithiophene), Di-NPB (N,N'-di-[(1-naphthyl)-N,N'-diphenyl]-1,1'-biphenyl)-4,4'-diamine), α-NPB (N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine), TNATA (4,4',4''-tris-(N-(naphthyl)-N-phenylamine)triphenylamine), BPAPF (9, 9-bis[4-(N,N-bis-biphenyl-4-yl-amino)phenyl]-9H-fluorene), spiro-NPB (N2,N7-di-1-naphthalenyl-N2,N7-diphenyl-9,9'-spirobi[9H-fluorene]-2,7-diamine), 4P-TPD (4,4-bis-(N,N-diphenylamino)-tetraphenyl), polyTPD (i.e., poly[N,N'-bis(4-butylphenyl)-N,N'-bisphenylbenzidine]), PTAA (i.e., poly(triarylamine), also known as poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]), or poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS). The p-type material may include carbon nanotubes. Typically, the p-type material is selected from spiro-OMeTAD, P3HT, PCPDTBT, polyTPD, PEDOT:PSS, spiro(TFSI)2 and PVK.

[0229] Suitable p-type materials also include molecular hole transporters, polymeric hole transporters and copolymeric hole transporters. The p-type material can be, for example, a molecular hole transport material, a polymer or a copolymer that includes one or more of the following moieties: thiophenyl, phenelenyl, dithiazolyl, benzothiazolyl, diketopyrrolopyrrolyl, ethoxydithiophenyl, amino, triphenylamino, carbozolyl, ethylenedioxythiophenyl, dioxythiophenyl, or fluorenyl.

[0230] The p-type material may be doped, for example, with tertbutylpyridine and LiTFSI. The p-type material may be doped to increase the hole density. The p-type material may be doped, for example, with NOBF4 (nitrosonium tetrafluoroborate) to increase the hole density.

[0231] Typically, hole transport material (p-type material) is a solid inorganic hole transport material.For example, p-type layer can include inorganic hole transporter, including nickel (e.g. NiO), vanadium, copper or molybdenum oxide; CuI, CuBr, CuSCN, Cu2O, CuO or CIS; perovskite; amorphous Si; p-type IV semiconductor, p-type III-V semiconductor, p-type II-VI semiconductor, p-type I-VII semiconductor, p-type IV-VI semiconductor, p-type V-VI semiconductor, and p-type II-V semiconductor, and this inorganic material can be undoped or doped.p-type layer can be a dense layer of said inorganic hole transporter.

[0232] The p-type material may be an inorganic p-type material, such as an oxide of nickel, vanadium, copper or molybdenum; CuI, CuBr, CuSCN, Cu2O, CuO or CIS; amorphous Si; a p-type IV semiconductor, a p-type III-V semiconductor, a p-type II-VI semiconductor, a p-type I-VII semiconductor, a p-type IV-VI semiconductor, a p-type V-VI semiconductor, and a p-type II-V semiconductor, which may be undoped or doped. The p-type material may include an inorganic hole transporter selected from, for example, CuI, CuBr, CuSCN, Cu2O, CuO and CIS.

[0233] Typically, the layer of hole transporting (p-type) material is a solid inorganic hole transporting material comprising an oxide of nickel, vanadium, copper or molybdenum. The solid inorganic hole transporting material typically exists as a dense layer. For example, the solid inorganic hole transporting material comprises nickel oxide, e.g., a dense layer of nickel oxide. The layer of hole transporting (p-type) material may comprise two sublayers, e.g., an inorganic p-type sublayer and an organic p-type sublayer. The inorganic p-type sublayer may be a layer of nickel oxide. The organic p-type sublayer may be a layer of polyTPD. The multijunction devices described herein may further include one or more buffer layers. For example, one or more buffer layers may be introduced between the electrode and the charge transport layer (electron transport (n-type) layer or hole transport (p-type) layer). The purpose of the buffer layer is both to improve the electronic and physical contact between the charge transport layer and the electrode, and to prevent damage to the charge transport layer and the photoactive layer due to or during the deposition of the electrode. The buffer layer may also prevent undesirable chemical interactions occurring at the point of physical contact between the electrode and the charge transport layer and / or the photoactive layer. Examples of buffer layers include SnO2, ZnO, MoO x , Al2O3Cr, CrO, LiF and BCP individual layers, combinations thereof or alloys thereof.

[0234] The multijunction devices described herein may further include one or more interface modification layers. Often, the properties of the surface of the perovskite layer, or the interface between the perovskite layer and the charge transport layer, may be improved by the inclusion of at least one interface modification layer. The improvement provided by the one or more interface modification layers may be one of the following properties: slower surface recombination of charge; improved charge extraction; change in energy level alignment at the interface, including improved open-circuit voltage; improved stability of the photoactive layer (e.g., a layer of the A / M / X material described herein), and / or improved stability of the A / M / X layer in contact with the charge extraction layer. The interfacial modification layer may include LiF; MgF2; AX, where A = Cs, Rb, Na, K, and X = I, Br, Cl, or F; AX, where A = an organic ammonium cation such as guanadinium as described herein, and X = I, Cl, Br, F, and pseudohalides; Al2O3, and other A / M / X passivators such as those described in WO2015092397A1.

[0235] The multijunction devices described herein may further include one or more optical spacer layers. Due to the properties of light, when light reflects off a metal surface, the nodes of the corrugation are located very close to the metal surface. This means that the light power density, i.e., the light intensity, is low in the area close to the metal reflective layer. In the devices described herein, a metal electrode may be used as a rear reflector. However, since the charge extraction layer may be very thin, the second photoactive layer is often in close proximity to this rear reflective metal layer. This therefore implies that the light power density, and subsequent light absorption, in the rear area of ​​the second photoactive layer is often low. To overcome this problem, an optical spacer layer between the second photoactive layer (and any buffer layer) and the second electrode may be included. This optical spacer layer must be highly transparent to light in the wavelength range of the spectral response of the second photoactive material. For example, it may be a transparent conductive oxide, such as ITO, AZO, or FTO. Preferably, the refractive index of the optical spacer layer is close to that of the second photoactive layer. The optical spacer layer can be TiO2, metal doped TiO2 or TiN. An example of a device with an optical spacer layer is shown in FIG.

[0236] The multijunction devices described herein can further include a first electrode. The first electrode may comprise a metal (e.g., silver, gold, aluminum or tungsten) or a transparent conductive oxide (e.g., fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO) or indium-doped tin oxide (ITO)). Typically, the first electrode is a transparent electrode. Thus, the first electrode typically comprises a transparent conductive oxide, preferably FTO, ITO or AZO. The layer thickness of the first electrode is typically from 5 nm to 100 nm.

[0237] The multijunction devices described herein may further include a second electrode. The second electrode may be as defined above for the first electrode. Typically, the second electrode comprises or consists essentially of a metal, e.g., an elemental metal. Examples of metals that the second electrode material may comprise or consist essentially of include silver, gold, copper, aluminum, molybdenum, platinum, palladium, or tungsten. The second electrode may be disposed by vacuum deposition. The layer of the second electrode material typically has a thickness of 1 to 250 nm, preferably 50 nm to 150 nm.

[0238] Thus, the multijunction devices described herein may further include a first electrode and a second electrode. Typically, the multijunction devices may include the following layers in the following order: - a first electrode as described herein; - any buffer layer as described herein; - a hole transporting (p-type) layer as described herein; - any interfacial modification layer as described herein; - a layer of a first photoactive material as described herein; - any interfacial modification layer as described herein; - an electron transporting (n-type) layer as described herein; - any buffer layer as described herein; - a charge recombination layer as described herein; - any buffer layer as described herein; - a hole transporting (p-type) layer as described herein; - any interfacial modification layer as described herein; - a layer of a second photoactive material as described herein; - any interfacial modification layer as described herein; - an electron transporting (n-type) layer as described herein; - any buffer layer as described herein; - a second electrode as described herein.

[0239] Typically, the first electrode comprises a transparent conductive oxide, preferably ITO, AZO or FTO, and the second electrode comprises an elemental metal, preferably silver, gold, molybdenum or tungsten.

[0240] In one embodiment, the multijunction device may comprise the following layers in the following order: - a first electrode comprising a preferably transparent conductive oxide as described herein; - a hole transporting (p-type) layer as described herein; - a layer of a first photoactive material as described herein, wherein the first photoactive material comprises at least one A / M / X material; - an electron transporting (n-type) layer as described herein; a charge recombination layer comprising a charge recombination layer material, preferably comprising (a) TiO2 or metal-doped TiO2 as described herein, and optionally (b) a transparent conductive oxide as described herein; - a hole transporting (p-type) layer as described herein; - a layer of a second photoactive material as described herein, where the second photoactive material comprises a compound that is a photoactive semiconductor other than an A / M / X material; - an electron transporting (n-type) layer as described herein; - any optical spacer layer as described herein; - a second electrode, preferably comprising an elemental metal or a transparent conductive oxide as described herein.

[0241] The multijunction device may further include any of the buffer layers and any of the interfacial modification layers described herein. The charge recombination layer may include a layer of the charge recombination layer material described herein and one or more additional layers.

[0242] In another embodiment, the multijunction device may comprise the following layers in the following order: - a first electrode comprising a preferably transparent conductive oxide as described herein; - hole transport (p-type) layer; - a layer of a first photoactive material as described herein, wherein the first photoactive material comprises at least one A / M / X material; - Electron transport (n-type) layer; a charge recombination layer comprising a charge recombination layer material, preferably comprising (a) TiO2 or metal-doped TiO2 as described herein, and optionally (b) a transparent conductive oxide as described herein; - hole transport (p-type) layer; - a layer of a second photoactive material as described herein, where the second photoactive material comprises at least one A / M / X material; - Electron transport (n-type) layer; - any optical spacer layer as described herein; - a second electrode, preferably comprising an elemental metal or a transparent conductive oxide as described herein.

[0243] The multijunction device may further include any of the buffer layers and any of the interfacial modification layers described herein. The charge recombination layer may include a layer of the charge recombination layer material described herein and one or more additional layers.

[0244] The multijunction device may be an optoelectronic device. The optoelectronic device includes a photovoltaic device, a photodiode (including a solar cell), a phototransistor, a photomultiplier, a photoresistor, or a light-emitting device. Typically, the multijunction device is a photovoltaic device or a light-emitting device. Preferably, the multijunction device is a positive intrinsic negative (pin) planar heterojunction photovoltaic device.

[0245] The multijunction device of the present invention can be a multijunction light emitting device, where multiple junctions of different band gap light emitting diodes produce a composite white emission.

[0246] Manufacturing method The multi-junction device of the present invention can be fabricated by sequential deposition of each layer onto a substrate. Typically, the substrate is a transparent substrate such as glass, and each layer is deposited in turn to build a stack of layers that form the multi-junction device structure. Some or all of the layers can be deposited by liquid deposition, such as gravure coating, slot-die coating, screen printing, inkjet printing, doctor blade coating, spray coating, roll-to-roll (R2R) processing, or spin coating. Typically, some of the layers are deposited by spin coating.

[0247] For example, a multijunction device may - providing a substrate, typically a transparent substrate such as glass; - depositing a first electrode, typically comprising a transparent conductive oxide, onto a substrate; - Optionally deposit a charge transport layer, typically a p-type layer; - depositing a layer of a first photoactive material; - Depositing an optional charge transport layer, typically an n-type layer; - Depositing a charge recombination layer; - Optionally deposit a charge transport layer, typically a p-type layer; - depositing a layer of a second photoactive material; - Depositing an optional charge transport layer, typically an n-type layer; - Depositing a second electrode, typically comprising an elemental metal The composition can be produced by the method described above.

[0248] Methods for the deposition of n-type and p-type layers, deposition of A / M / X materials, deposition of photoactive semiconductors other than A / M / X materials, and deposition of electrodes are well known in the art and are described in published patent applications WO2013 / 132236, WO2013 / 171517, WO2013 / 171518, WO2013 / 171520, WO2014 / 045021, WO2014 / 045022, WO2014 / 045023, WO2014 / 045024, WO2014 / 045025, WO2014 / 045026, WO2014 / 045028, WO2014 / 045029 ... No. 4 / 191767, WO2014 / 202965, WO2015 / 092397, WO2015 / 140548, WO2016 / 005758, WO2016 / 020699, WO2017 / 060700, WO2017 / 037448, WO2017 / 089819, WO2017 / 153752 and WO2018 / 193267. The multijunction devices of the present invention may be prepared according to the methods set forth in these documents using the materials described herein.

[0249] Typically, the first electrode is disposed on the substrate by sputter coating.

[0250] Typically, the deposition of the charge transport layer involves forming a solution or dispersion of n-type or p-type materials or n-type or p-type precursors in a solvent and spin-coating the solution or dispersion onto the layer stack. Usually, the solution-processed layer stack is dried to remove the solvent. Removal of the solvent may involve heating the solvent or evaporating the solvent.

[0251] At least one of the layers of photoactive material comprises at least one A / M / X compound as described herein. Such A / M / X compounds may be deposited on the device stack by disposing at least one film-forming solution comprising one or more A cations, one or more M cations and one or more X anions as described herein. The film-forming solution may be disposed on the device stack by gravure coating, slot die coating, screen printing, inkjet printing, doctor blade coating, spray coating, roll-to-roll (R2R) processing, or spin coating, typically by spin coating.

[0252] The charge recombination layer may be disposed on the substrate by solution-based techniques or other techniques such as vacuum deposition or sputter coating, depending on the choice of charge recombination layer material.

[0253] Typically, when the charge recombination layer comprises TiO2, metal-doped TiO2 (e.g., Nb-doped TiO2), or a mixture of TiO2 or metal-doped TiO2 with a transparent conductive oxide, the charge recombination layer is deposited onto the device stack by sputter coating.

[0254] Typically, the second electrode is deposited by vacuum evaporation.

[0255] Working Example The advantages of the present invention are described hereinafter with reference to some specific embodiments.

[0256] Example 1 Optical and Device Modeling We implemented an optical model (generalized transfer matrix method) [Charalambos C. Katsidis and Dimitrios I. Siapkas, Applied Optics 41, no. 19 (2002): 3978] and a detailed balance-based device model [Kristofer Tvingstedt et al., Scientific Reports 4 (2014): 1-7] to simulate the effect of the index-matching interlayer. The transfer matrix method is a recalculation of Maxwell's equations for calculating electromagnetic wave propagation in any layered medium, such as a solar cell stack. The model fully accounts for interference. It uses the optical constants and layer thicknesses to calculate the absorptivity A(λ), which is treated as the external quantum effect (EQE(λ)) of the cell. We then implemented a detailed balance (assuming state-of-the-art, series resistance R s , shunt resistance R sh , ideality factor n id and electroluminescence external quantum effect EQE EL ) was used to calculate the J-V curves and therefore completely determine the device performance.

[0257] Optimized ITO interlayer The interlayer works best when the two reflections (Figure 2a) can destructively interfere. Even with a wildly mismatched ITO interlayer, the dip in the EQE can be reduced if the correct thickness is chosen. Unfortunately, this optimum thickness falls between 150-200 nm for the ITO interlayer. This is thicker than ideal from a manufacturing and material use standpoint, due to the cost and scarcity of indium. Moreover, even below this optimum ITO thickness, there is still significant reflection. More practical thicknesses - 100 to 120 nm - fall off strictly in the region that maximizes reflection. Thus, ITO is optically unsuitable for use as an interlayer. It only serves to worsen reflection at all thicknesses. In fact, the tandem is considered to reflect a minimum when the ITO layer is scaled down to 0 nm. This is, of course, an unrealistic thickness if its presence is required to allow either charge recombination or to act as a solvent barrier. For solvent barrier functionality, the ITO layer should probably be in the range of 100 nm in thickness.

[0258] rate-matched recombination layer Rate-matched interlayers do not suffer from the problems that ITO has. top (λ) and n bot Let (λ) be the refractive index of the upper and lower absorbers, respectively. Then

[0259]

number

[0260] The refractive index of the non-absorbing intermediate layer is given by

[0261]

number

[0262] , which minimizes the reflection at λ0. The thickness must also minimize the total reflection for all wavelengths, also taking into account the incident spectrum. However, real interlayers are not completely transparent, especially if they are electronically doped. This pushes the optimum refractive index for the interlayer towards a higher refractive index in order to minimize reflectance losses at smaller thicknesses.

[0263] Optical calculations reveal that an interlayer with a refractive index of 2.0-2.5 (700-1000 nm) maximizes the current. In such an interlayer, the current is also less sensitive to the selected interlayer thickness. In the model, the power conversion efficiency (PCE) of the tandem perovskite cell using an optimized ITO thickness of 203 nm is estimated to be 28.8%. The best index match-interlayer (n = 2.45, t = 50 nm) shows an absolute gain of 0.6%, increasing the PCE to 29.38%. However, 203 nm ITO is unrealistic as explained before. The choice of refractive index of 2.45, I, was based on the optimal value from the model. However, there are few real materials that are both highly transparent (wide band gap) and have this high refractive index. A more realistic value of ~2.2 can be achieved by many materials. In a more realistic scenario of n = 2.2 and t = 100 nm, the PCE advantage of replacing ITO for a 2.2 index material is an absolute gain of over 1%, which is shown in Figure 4d.

[0264] High refractive index material As our calculations show (FIG. 4), a recombination layer with a high refractive index n(850 nm)>2.0 can provide an absolute increase in PCE of one 1%.

[0265] Such a recombination layer: High refractive index (n>2.0), where the lower cell absorbs (650-1100 nm). Low absorption coefficient (α<10 between 650-1100 nm) 3 cm -1 ). Wide band gap semiconductors are suitable. Low resistivity (<500 Ωcm) (allowing low loss recombination of electrons and holes) needs to be satisfied.

[0266] In essence, this is similar to the family of materials suitable for the fabrication of TCOs. Unfortunately, high-index TCOs are rare due to the rule of thumb mentioned above: wide-bandgap semiconductors tend to have low refractive indices. There are a few exceptional ceramics that have high refractive indices: TiO2[n 900nm = 2.3], rTiO3[2.33], Cr2O3[2.5], CuCrO2[2.6], ZnS [2.3], ZrO2[2.12], AlN [2.1], GaN [2.3].

[0267] TiO2 is a suitable high-rate replacement for ITO or FTO. TiO2 has high conductivity, especially when doped with Nb, and absorbs less light than ITO across the visible-IR spectrum. The low-temperature processed phase, rutile TiO2, has suitable conductivity and mobility for the recombination layer. Low-temperature processing is also advantageous since organic-inorganic perovskite materials cannot withstand high temperatures. Unlike the electrodes, there is no need for long-term lateral conduction in the recombination layer, and in fact it is advantageous to have low lateral conduction, since it minimizes the risk of shorting the device by intermediate layers. This is particularly important when turning the monolithically deposited layers into modules where a series interconnection between the top and bottom electrodes is required. Considering the series resistance perpendicular to the substrate through the cell, it is 10 4 Even a high resistivity of Ωcm causes a negligible voltage drop of about 1 mV in a 100 nm thick recombination layer. Nb:TiO2 films have a 6·10 -1 A resistivity of Ωcm was achieved. [Ben Jemaa et al., Journal of Materials Science: Materials in Electronics 27, no. 12 (2016): 13242-48]

[0268] Nb:TiO2 intermediate layer Nb:TiO2 is a promising high refractive index interlayer. Nb:TiO2 / ITO mixtures can also be used to tune the refractive index and also to improve the electronic contact, where the advantageous electronic properties of ITO can be combined with the optical properties of TiO2. We calculate the performance of a tandem with a Nb:TiO2 / ITO mixed interlayer (Figure 5). At a thickness of 100 nm, the 60 / 40 Nb:TiO2 / ITO mixed recombination layer gives an absolute PCE gain of 0.8%.

[0269] Improved angular insensitivity Lab-measured PCE paints an incomplete picture of the cell's performance in the real world. Laboratory measurements are typically performed under a simulated direct incidence AM1.5 spectrum. Cells are also optimized for performance under such conditions. However, the spectral composition of sunlight can vary quite significantly depending on location, time, cloud cover, humidity and dust. Furthermore, the angle of incidence varies throughout the day and year. On cloudy or foggy days, most of the incident light is diffuse and strikes the panel from all angles. At direct incidence, the TiO2 index-matched stack shows a gain of 1.1% (absolute) over the ITO stack. The improvement in power conversion efficiency is seen over the entire range of incidence angles (Figure 6). This is particularly important in cloudy locations such as the UK, where diffuse light can sometimes dominate.

[0270] Reduced sensitivity to thickness changes In principle, these optimum thicknesses for the tandem cell layers can be calculated using a transfer matrix-based optical model. In practice, this exact optimum cannot be achieved since there is random variation in thickness during manufacturing. This effect causes the actual cells to have lower efficiency than the optimum. Modeling shows that rate-matched cells are more insensitive to thickness variations than mismatched cells. This results in a corresponding increase in

[0271] We simulate a batch of 1000 cells with absorber and recombination layer thicknesses normally distributed around the optimum with a 5% standard deviation (Figure 7). For the batch of cells with ITO (28.28% optimum), the average PCE is 27.86%, a degradation of -0.42%. For the cells with TiO2 (29.46% optimum), the average PCE is 29.23%, a degradation of -0.16%.

[0272] Example 2 - Preparation of NbTiO2 thin film 80 nm NbTiO2 films were formed on silicon and glass substrates by sputter coating from a 4% Nb-doped TiO2 target. The substrates were cleaned prior to deposition as follows. Silicone: Rinse successively in acetone and IPA and blow dry. Glass: Sonicated sequentially in DECON90, deionized water, acetone, and IPA for 2 minutes each, then blown dry. First, I ran the cleaning recipe with the following settings: - Initial chamber pump down to 9e-6 Torr - Set Argon to 18 SCCM (Standard Cubic Centimeters Per Minute) - 100W HIPIMs (High Power Impulse Magnetron Sputtering) on ​​4 inch targets - Average current 800 mA - Pulse frequency 750 Hz - Pulse width 50 μs - Pressure set point 5 mTorr - Sputter for 20 minutes

[0273] The deposition was then carried out with the following deposition run settings: - Initial chamber pump down to 2e-6 Torr - Board rotation 10 rpm - Sample stage at 30 °C. - Set Argon to 18 SCCM - 100W HIPIMs on 4 inch targets - Average current 800mA - Pulse frequency 750Hz - Pulse width 50μs - Pressure set point 5mTorr - Sputter for 30.5 minutes for surface cleaning - Set O2 to 6 SCCM - Wait 19.5 minutes - Open the shutter and lower the stage to 4 inches - 4 hour deposit time - The sample stage temperature was increased to 70 °C for the remaining hour of deposition.

[0274] The optical constants n and k were determined using ellipsometry. The ellipsometry data was measured on 80 nm sputtered Nb-doped (4%) TiO2 films on silicon wafers. The instrument used was a JA Woollam RC2 ellipsometer. The results of the tests are shown in Figure 9. The data in Figure 9 show that the refractive index of the layer, n, was greater than 2 for all wavelengths between 500 and 1200 nm.

[0275] The transmittance and reflectance data for 80 nm thick Nb-doped (4%) TiO2 thin films sputtered on glass were collected using a Perkin Elmer 1050 with an integrating sphere attachment and are shown in Figure 10. The transmittance was greater than 60% for all wavelengths between 400 and 1200 nm.

Claims

1. a) a first photoactive region comprising a layer of a first photoactive material; b) a second photoactive region comprising a layer of a second photoactive material; and c) a charge recombination layer disposed between the first photoactive region and the second photoactive region; Including, wherein one of the first and second photoactive materials comprises at least one A / M / X material; wherein the other of the first and second photoactive materials comprises at least one A / M / X material or a compound that is a photoactive semiconductor other than an A / M / X material; wherein each A / M / X material is a crystalline compound of formula (I); [A] a [M] b [X] c (I) During the ceremony: [A] contains one or more A cations; [M] comprises one or more M cations which are metal or metalloid cations; [X] comprises one or more X anions; a is a number from 1 to 6; b is a number from 1 to 6; and c is a number from 1 to 18; and wherein the charge recombination layer material has a refractive index, n(λ), of at least 2 at a wavelength λ, where λ is a wavelength between 500 nm and 1200 nm; and wherein each photoactive region further comprises at least two charge transport layers; wherein the charge recombination layer material is (a) TiO 2 or metal-doped TiO 2 and (b) a transparent conductive oxide; or where the charge recombination layer material comprises a mixture of (a) and (b); Further wherein the charge recombination layer has a thickness of 50 to 150 nm. Multijunction devices.

2. The charge recombination layer material has a wavelength λ A The refractive index n(λ A ) and the first photoactive material has a wavelength λ A where n is the refractive index 1 (λ A ), where n 1 (λ A ) is n(λ A ), where λ A is a wavelength between 500 nm and 1200 nm that may be the same or different from λ; and / or The charge recombination layer material has a wavelength λ A The refractive index n(λ A ) and the second photoactive material has a wavelength λ A where n is the refractive index 2 (λ A ), where n 2 (λ A ) is n(λ A ), where λ A 2. The multijunction device of claim 1, wherein is a wavelength between 500 nm and 1200 nm that is the same as or different from λ.

3. 3. The multijunction device of claim 1 or 2, wherein the charge recombination layer material has a refractive index, n(λ), at wavelength λ, of less than 3.

5.

4. 4. The multijunction device of claim 3, wherein the charge recombination layer material has a refractive index at wavelength λ, n(λ), less than or equal to 2.

5.

5. The first photoactive material has a band gap Eg 1 wherein the charge recombination layer material has a band gap Eg and the second photoactive material has a band gap Eg 2 where: a) Eg 1 Eg 2 and / or b) Eg is Eg 1 and / or c) Eg is Eg 1 Larger than Eg 1 Eg 2 and Eg is at least 2.0 eV.

6. Eg is Eg 1 Larger than Eg 1 Eg 2 greater than 0.01 eV, Eg is at least 3.0 eV, and Eg 1 The multijunction device of claim 5 , wherein is less than or equal to 2.0 eV.

7. The multijunction device of any one of claims 1 to 6, wherein the charge recombination layer has a thickness of 75 to 150 nm.

8. The multijunction device of any one of claims 1 to 6, wherein the charge recombination layer has a thickness of 50 to 125 nm.

9. The charge recombination layer [0010] λ in the formula o is a wavelength between 500 nm and 1200 nm that may be the same or different from λ, and n is the λ of the charge recombination layer material. o is the refractive index at The multijunction device of any one of claims 1 to 8, having a thickness of about 1 nm.

10. (i) one of the first and second photoactive materials comprises at least one A / M / X material as defined in claim 1, and the other of the first and second photoactive materials comprises a compound that is a photoactive semiconductor other than an A / M / X material; or (ii) The multijunction device of any one of claims 1 to 9, wherein the first photoactive material comprises at least one crystalline A / M / X material as defined in claim 1, and the second photoactive material comprises at least one second A / M / X material as defined in claim 1, which is the same as or different from the first A / M / X material.

11. The multijunction device of claim 10 wherein the compound that is a photoactive semiconductor comprises a chalcogenide anion.

12. TiO 2 or metal-doped TiO 2 Transparent conductive oxide and TiO 2 or metal-doped TiO 2 at least 20% by volume of the total volume of or TiO 2 or metal-doped TiO 2 Transparent conductive oxide and TiO 2 or metal-doped TiO 2 is at least 50% by volume of the total volume of or TiO 2 or metal-doped TiO 2 Transparent conductive oxide and TiO 2 or metal-doped TiO 2 The multijunction device of any one of claims 1 to 11, wherein the multijunction device is at least 80% by volume of the total volume of the multijunction device.

13. Charge recombination layer material is metal-doped TiO 2 13. The multijunction device of claim 12, comprising:

14. The multijunction device of claim 13 wherein the metal is selected from Ta, V and Nb.

15. The multijunction device of claim 14 wherein the metal is Nb.

16. Metal-doped TiO 2 The metal in the TiO 2 present in an amount of at least 0.5% by weight of the total weight of or Metal-doped TiO 2 The metal in the TiO 2 present in an amount of 1 to 10% by weight of the total weight of or Metal-doped TiO 2 The metal in the TiO 2 The multijunction device of any one of claims 13 to 15, wherein the multijunction device is present in an amount of 2 to 6 weight percent of the total weight of the device.

17. TiO 2 The multijunction device of any one of claims 13 to 16, wherein is in the rutile phase.

18. The multijunction device of any one of claims 1 to 17, wherein [A] comprises one or more A cations, including at least one organic cation.

19. Each A cation is Cs + , Rb + 19. The multijunction device of any one of claims 1 to 18, wherein the cation is selected from the group consisting of methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, septylammonium, octylammonium, tetramethylammonium, formamidinium, 1-aminoethane-1-iminium and guanidinium.

20. The multijunction device of any one of claims 1 to 19, wherein [M] comprises two or more different M cations.

21. The multijunction device of any one of claims 1 to 20, wherein each M cation is a dication.

22. Each M cation is Ca 2+ , Sr 2+ , Cd 2+ , Cu 2+ , Ni 2+ , Mn 2+ , Fe 2+ , Co 2+ , Pd 2+ , Ge 2+ , Sn 2+ , Pb 2+ , Yb 2+ and Eu 2+ 22. The multijunction device of claim 21 , selected from:

23. Each M cation is Sn 2+ and Pb 2+ 23. The multijunction device of claim 22 selected from:

24. The multijunction device of any one of claims 1 to 23, wherein each X anion is a halide.

25. 25. The multijunction device of claim 24, wherein [X] comprises two or more different halide anions.

26. Formula [A] a [M] b [X] c The compound of formula [A][M][X] 3 26. The multijunction device of any one of claims 1 to 25, wherein [A], [M] and [X] are as defined in any one of claims 1 and 20 to 23.

27. The multijunction device of any one of claims 1 to 26, wherein each photoactive region further comprises an electron transport (n-type) layer and a hole transport (p-type) layer.

28. 30. The multijunction device of claim 27, wherein each photoactive region comprises a layer of photoactive material disposed between an electron transport (n-type) layer and a hole transport (p-type) layer.

29. The multijunction device of any one of claims 1 to 28, further comprising an optical spacer layer.

30. The optical spacer layer is a transparent conductive oxide, TiO 2 , metal-doped TiO 2 or TiN.

31. The multijunction device of any one of claims 1 to 30, wherein the multijunction device is a photovoltaic or light emitting device.

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