Solar cell

Abstract

To provide a solar cell having improved power conversion efficiency, as well as improved stability and lifespan, and provide a solar cell having high rectification resulting in a high fill factor.SOLUTION: A solar cell includes a first electrode, a second electrode, and a layer stack disposed between the first and second electrodes. The layer stack includes a light-absorbing layer having a perovskite crystal structure and at least one dopant layer. The dopant layer is made of one or more n-type dopant materials or one or more p-type dopant materials.SELECTED DRAWING: Figure 2

Description

Detailed Description of the Invention

[0001] The present disclosure relates to solar cells.

[0002] 〔background〕 Thin-film photovoltaics are a key technology for future low-cost, sustainable renewable energy sources. Organic-inorganic (hybrid) lead halide perovskite solar cells have been proposed for photovoltaic applications due to their impressive power conversion efficiencies (PCEs), currently exceeding 21% (see Kojima et al., J. Am. Chem. Soc. 131, 6050-6051 (2009); Lee et al., Science 338, 643-647 (2012); Yang et al., Science 348, 1234-1237 (2015)). Perovskite thin-film absorbers can be deposited by simple solution or sublimation processes, thus offering the potential for inexpensive photovoltaic devices. The high PCE is due to the exceptionally high absorption coefficient and mobility of photogenerated electrons and holes in the hybrid perovskite.

[0003] To produce high-performance solar cells, uniform perovskite films with high crystallinity are required to reduce trap concentrations and achieve sufficient charge carrier mobility (see Nie et al., Science 347, 522-525 (2015)). The use of the archetype perovskite, methylammonium lead iodide (MAPbI3), can lead to highly efficient devices. Furthermore, further reduction of the bandgap by the addition of formamidinium (FA) allows for the collection of additional near-infrared photons (see Pellet et al., Angewandte Chemie International Edition 53, 3151-3157 (2014)). When such mixed-organic cation perovskites are further stabilized by substituting some of the iodide with bromide, a champion material for perovskite cells, i.e., (FAPbI3), is developed. 1-x (MAPbBr3) x (References: Yang et al., Science 348, 1234-1237 (2015); Jeon et al., Nature 517, 476-480 (2015); Bi et al., Science Advances 2 (2016)).

[0004] Various solar cell architectures have been used. One of these architectures is derived from dye-sensitized solar cells and consists of a transparent conductive substrate. The transparent conductive substrate is coated with a mesoporous or planar TiO layer (n-type, thus functioning as an electron transport layer, or ETL) to which a perovskite light-absorbing layer is added. A hole transport layer (HTL, p-type), usually an organic semiconductor, is then solution-deposited on top of the perovskite. The device is then finished with a deposited top electrode (see: Stranks et al., Science 342, 341-344 (2013); Eperon et al., Advanced Functional Materials 24, 151-157 (2014); Conings et al., Advanced Materials 26, 2041-2046 (2014); and Chen et al., Journal of the American Chemical Society 136, 622-625 (2014)).

[0005] Another configuration is inverted compared to the above configuration. A conductive substrate is coated with an HTL. Then, following the perovskite absorber and ETL, the conductive substrate is coated with a suitable evaporated top electrode (see Wu et al., Energy & Environmental Science 8, 2725-2733 (2015); Zhou et al., Science 345, 542-546 (2014)). These two device configurations are classified as "conventional" and "inverted." However, these devices are also referred to as nip and pn devices.

[0006] Chen et al. (Science 350, 944-948 (2015)) demonstrated that (i) the PCE in planar devices can be limited by the conductivity of the metal oxide layers and that (ii) this trend can be enhanced by doping these layers. This was achieved by adding heteroatoms with different valences to aqueous-processed metal oxides. However, only a small increase in conductivity (about one order of magnitude) was achieved. Therefore, only very thin metal oxide transport layers (<20 nm) can be used. Without such metal oxide transport layers, the PCE would be significantly reduced.

[0007] Most reported organic-inorganic (hybrid) lead halide perovskite solar cells using vacuum-deposited perovskite absorber layers use charge transport layers processed from aqueous solutions. A fully vacuum-processed solar cell device would offer the additional advantages of (i) compatibility with temperature-sensitive substrates, (ii) enabling conformal coating on non-planar substrates, and (iii) direct application to tandem solar cells (see Polander et al., APL Materials 2, 081503 (2014)). In addition to the sophisticated deposition system required for vacuum processing, these solar cells have long demonstrated high throughput and reliability and have been used in the electronics industry (Ono et al., Journal of Materials Chemistry A (2016)).

[0008] By selecting a specific hole-transporting molecule with respect to the energy levels of the conduction and valence bands of perovskite, a high open-circuit voltage (Voc) of 1.1 V was demonstrated (Polander et al., APL Materials 2, 081503 (2014); Kim et al., Organic Electronics 17, 102-106 (2015), Ono et al., Journal of Materials Chemistry A (2016)). The highest efficiency (15.4%) was measured for a device with significantly higher hysteresis (a PCE of 14.0% was obtained for the same cell measured in the opposite bias scan direction). In this device, a single layer of an undoped organic molecule was used as the charge extraction layer (see Ke et al., Journal of Materials Chemistry A 3, 23888-23894 (2015)).

[0009] EP3242340A1 discloses a solar cell. The solar cell comprises: (i) a first electrode; (ii) a second electrode; and (iii) a layer stack (a stack of layers) disposed between the first electrode and the second electrode. The layer stack includes a light-absorbing layer. The light-absorbing layer includes an absorber compound having a perovskite crystal structure. It further discloses that (i) a p-type dopant layer is disposed between the first electrode and the light-absorbing layer, and (ii) an n-type dopant layer is disposed between the light-absorbing layer and the second electrode.

[0010] Current solar cells may suffer from low open circuit voltage, low short circuit current, low efficiency, short lifetime, and / or low fill factor.

[0011] 〔overview〕 Therefore, one object of the present invention is to provide a solar cell that overcomes the drawbacks of the prior art, and in particular to provide a solar cell that has improved power conversion efficiency as well as improved stability and lifespan. A further object is to provide a solar cell that has high rectification resulting in a high fill factor.

[0012] The above-mentioned object is achieved by the following solar cell, which comprises a first electrode, a second electrode, and a layer stack provided between the first electrode and the second electrode. The layer stack comprises a light absorbing layer having a perovskite crystal structure and at least one dopant layer. The at least one dopant layer is made of one or more n-type dopant materials or one or more p-type dopant materials. In one embodiment, multiple dopant layers of the same type (either n-type or p-type) may be provided in the same layer stack.

[0013] In the context of the present invention, when reference is made to "at least one dopant layer," it refers to each and every one of a plurality of layers unless expressly stated otherwise.

[0014] According to the present invention, the layer stack comprises one light absorbing layer and at least one dopant layer. In this respect, it should be understood that the layer stack comprises exactly one light absorbing layer (not two or more light absorbing layers) and exactly one type of dopant layer (either n-type or p-type). In other words, if the layer stack provided in the solar cell of claim 1 comprises only one dopant layer, then this one dopant layer is either n-type or p-type. If the layer stack provided in the solar cell comprises two or more dopant layers, then (First alternative) All dopant layers included in a single layer stack are n-type (i.e., all dopant layers are formed by one or more n-type dopant materials); or (Second alternative) all of the dopant layers are p-type (i.e., all of the dopant layers are formed by one or more p-type dopant materials); Either:

[0015] In one embodiment, the layer stack comprises one light absorbing layer and one dopant layer.

[0016] In another embodiment, the layer stack comprises one light absorbing layer and two or more dopant layers, and the two or more dopant layers are all either n-type or p-type, i.e., the two or more dopant layers are all (i) formed of one or more n-type dopant materials, or (ii) formed of one or more p-type dopant materials.

[0017] In a first alternative, at least one dopant layer consists of one or more n-type dopant materials. In a second alternative, the dopant layer consists of one or more p-type dopant materials. In this regard, the term "consisting of" means that the dopant layer exclusively contains one type of dopant material (i.e., either a single n-type dopant material / a mixture of multiple different n-type dopant materials, or a single p-type dopant material / a mixture of multiple different p-type dopant materials), but does not include (i) a mixture of p-type and n-type dopant materials, or (ii) a mixture of each of multiple dopant materials with other materials.

[0018] In particular, at least one dopant layer may be free of any charge transport material. Each of the exemplary charge transport materials disclosed herein is not intended to be limiting.

[0019] In embodiments in which the layer stack in a solar cell includes two or more dopant layers, the two or more dopant layers are separated (isolated) by a layer of charge transport material. In this embodiment, the dopant layers are in direct contact with adjacent layers of charge transport material. These layers of charge transport material do not contain either n-type or p-type dopants. The use of such layers of charge transport material can increase the power conversion efficiency of the solar cell or can increase the stability and lifetime of the solar cell of the present invention.

[0020] In another embodiment, the dopant layer and the electrode are separated by a layer of charge transport material. In this embodiment, the layer of charge transport material (i) directly contacts the adjacent dopant layer on one side and (ii) directly contacts the electrode on the other side. The layer of charge transport material does not contain either an n-type or a p-type dopant. The use of such a layer of charge transport material can increase the power conversion efficiency of the solar cell or the stability and lifetime of the solar cell of the present invention.

[0021] In another embodiment, the dopant layer and the light-absorbing layer are separated by a layer of charge transport material. In this embodiment, the layer of charge transport material (i) directly contacts the adjacent dopant layer on one side and (ii) directly contacts the light-absorbing layer on the other side. The layer of charge transport material does not contain either an n-type or a p-type dopant. The use of such a layer of charge transport material can increase the power conversion efficiency of the solar cell or the stability and lifetime of the solar cell of the present invention.

[0022] The layer stack may include a variety of additional layers in addition to one light-absorbing layer and at least one dopant layer.

[0023] According to the invention, if an n-type dopant layer is present in a (single) layer stack, then no p-type dopant layer is present in the same layer stack, and if a p-type dopant layer is present in a layer stack, then no n-type dopant layer is present in the same layer stack, i.e. the presence of pure dopant layers of further types in addition to at least one dopant layer in a single layer stack is excluded.

[0024] Surprisingly, the inventors have found that by inserting one type of thin dopant layer between the electrode and the perovskite absorber layer, the power conversion efficiency of the solar cell is increased, while the stability and lifetime are significantly improved.

[0025] Furthermore, the inventors have surprisingly found that the same layer stack referred to herein can result in a diode with high rectification (as evidenced by a high fill factor) by using only one type of dopant layer on only one side of the light absorbing layer in the same layer stack. The general architecture identified herein can result in highly efficient and reasonably stable solar cells. The architecture can be used in a wide range of planar perovskite solar cells and multi-junction architectures.

[0026] The solar cell includes a first electrode, a second electrode, and at least one layer stack disposed between the first electrode and the second electrode. The at least one layer stack includes a first light absorbing layer. The first light absorbing layer may have a thickness of about 200 nm to about 700 nm. The first light absorbing layer includes an absorber compound having a perovskite crystal structure.

[0027] In one embodiment, the at least one dopant layer may include two or more dopant sublayers. All of the dopant sublayers are of the same type (either p-type or n-type) as the at least one dopant layer. That is, if the at least one dopant layer is made of one or more n-type dopant materials, all of the dopant sublayers are made of n-type dopant materials. The n-type dopant materials may be the same or different from each other. Similarly, if the at least one dopant layer is made of one or more p-type dopant materials, the at least one dopant layer is made of one or more p-type dopant materials. The p-type dopant materials may be selected to be the same material or different from each other.

[0028] A solar cell of the present invention may include only one layer stack. In alternative embodiments, a solar cell may include two or more different layer stacks. A layer stack according to the present invention is a layer stack including exactly one light-absorbing layer and exactly one type of dopant layer. The at least one dopant layer in the layer stack may be (i) one or more n-type dopant materials or (ii) one or more p-type dopant materials. In embodiments in which a solar cell includes two or more different layer stacks, all of the layer stacks may include at least one dopant layer of the same type (e.g., only n-type or only p-type). Alternatively, each stack may individually include at least one dopant layer of a different type.

[0029] When a solar cell includes two or more layer stacks, the different layer stacks may be spaced apart from one another and connected to one another by an interconnecting layer. The interconnecting layer is disposed between (i) the first electrode and the second electrode and (ii) the first layer stack and the second layer stack. The interconnecting layer is in direct contact with both layer stacks. Each interlayer and the materials for forming the interlayer are known from the prior art, for example, WO2007 / 071451A1, WO08 / 077615A1, or WO2010 / 132236A1. In the context of the present disclosure, the interconnecting layer is not the at least one dopant layer.

[0030] In one embodiment, the at least one dopant layer is disposed between the first electrode and the light absorbing layer.

[0031] In a further embodiment, the at least one dopant layer is disposed between the second electrode and the light-absorbing layer.

[0032] In a further embodiment, the at least one dopant layer is in direct contact with the first electrode.

[0033] In one embodiment, the at least one dopant layer is in direct contact with the second electrode.

[0034] In a further embodiment, the at least one dopant layer is in direct contact with the light-absorbing layer.

[0035] In a further embodiment, the solar cell includes (i) two or more layer stacks and (ii) optionally at least one interconnect layer, the interconnect layer being disposed between two different layer stacks.

[0036] In one embodiment, the p-type dopant material is an organic compound, a metal organic compound, or an organometallic compound. The total amount of electron-withdrawing groups in the organic compound, the metal organic compound, or the organometallic compound is from 17 atomic percent to 90 atomic percent. The electron-withdrawing groups are independently selected from the group consisting of fluorine, chlorine, bromine, and CN.

[0037] In further embodiments, the total number of electron-withdrawing groups in the organic, organometallic, or organometallic p-type dopant material may be four or more.

[0038] In a further embodiment, the n-type dopant material is selected from the group consisting of metals, metal salts, metal complexes, and mixtures thereof.

[0039] In one embodiment, the metal is selected from the group consisting of alkali metals, alkaline earth metals, transition metals, and mixtures thereof.

[0040] In a further embodiment, the transition metal is selected from the rare earth metals.

[0041] In a further embodiment, the metal salt is selected from the group consisting of alkali metal salts, alkaline earth metal salts, rare earth metal salts, and mixtures thereof.

[0042] In a further embodiment, the alkali metal salt is selected from the group consisting of LiF, LiCl, LiBr, LiI, and mixtures thereof. Alternatively, the alkali metal salt is LiF.

[0043] In one embodiment, the metal complex is an organic alkali metal complex, an alkali metal complex, LiQ, an alkali borate, or a mixture thereof.

[0044] In a further embodiment, the at least one dopant layer has a thickness of 0.1 to 25 nm. Alternatively, the at least one dopant layer has a thickness of 0.1 to 10 nm. Alternatively, the at least one dopant layer has a thickness of 0.1 to 5 nm. Alternatively, the at least one dopant layer has a thickness of 0.1 to 3 nm.

[0045] In a further embodiment, the at least one dopant layer is a self-assembled monolayer.

[0046] Ultimately, the above object is achieved by a solar panel (solar panel) comprising the solar cell defined herein.

[0047] In the following, the layers and materials of said layers that can be used in accordance with the present invention are described in detail.

[0048] (p-type dopant) According to the present invention, the p-type dopant (=p-type dopant material) may be an organic compound, a metal-organic compound, or an organometallic compound. The amount of electron-withdrawing groups in the organic compound (each an organometallic compound) is preferably 17 to 90 atomic percent (atomic percentage). The electron-withdrawing groups in this case are preferably independently selected from the group consisting of fluorine, chlorine, bromine, and CN.

[0049] As used herein, the amount of electron-withdrawing groups in a sum formula of a p-type dopant is given in atomic percent (%) of the electron-withdrawing group relative to the total number of atoms in the sum formula.

[0050] For clarity of definition and calculation, the above summation formula has been simplified so that an electron-withdrawing group counts as one atomic unit even if it consists of more than one atom.

[0051] According to the present invention, electron withdrawing groups are defined as being selected from the group consisting of fluorine, chlorine, bromine and / or CN only.

[0052] The atomic percent of electron-withdrawing groups is the percentage of electron-withdrawing groups relative to the total number of atoms and electron-withdrawing groups in the total formula of the p-type dopant.

[0053] The total number of atoms and electron-withdrawing groups in the p-type dopant is 4 or more.

[0054] The CN group counts as one electron-withdrawing group in the (simplified) total formula for the p-dopant.

[0055] The calculated amounts of electron-withdrawing groups for the charge transport materials are shown in Table 1.

[0056] [Table 1]

[0057] The calculated amounts of electron-withdrawing groups for p-type dopants are shown in Table 2.

[0058] [Table 2]

[0059] The p-type dopant material (p-type dopant) may be an organic p-type dopant. The organic p-type dopant may have a molecular weight of about 350 to about 1700. In another embodiment, the organic p-type dopant may have a molecular weight of about 350 to 800. A molecular weight within this range allows for an adequate evaporation rate during vacuum thermal evaporation.

[0060] The organic p-type dopant may have a first reduction potential equal to or greater than that of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, the first reduction potential being about 0.18 V as measured by cyclic voltammetry vs. Fc / Fc+ in acetonitrile at room temperature.

[0061] In one embodiment, the first reduction potential of the organic p-type dopant is equal to or more positive than the reduction potential of 2,2'-(perfluoronaphthalene-2,6-diylidene)dimalononitrile. The first reduction potential is about 0.25 V when measured under the same conditions by cyclic voltammetry vs. Fc / Fc+ in acetonitrile solution at room temperature. When the p-type dopant is selected in this range, high conductivity of the doped layer can be achieved.

[0062] (n-type dopant) The n-type dopant may be a molecular dopant containing an organic compound having a molecular weight of about 300 to about 1500. Alternatively, it may be a metal compound selected from the group consisting of a metal halide having a molecular weight of about 25 to about 500, a metal complex having a molecular weight of about 150 to about 1500, and a zero-valent metal selected from the group consisting of alkali metals, alkaline earth metals, transition metals, and rare earth metals.

[0063] In one embodiment, the n-type dopant is an organic molecular dopant having a molecular weight of about 300 to about 1200.

[0064] In another embodiment, the n-type dopant is a molecular dopant having a first oxidation potential more negative than about −0.20 V when measured under the same conditions by cyclic voltammetry versus Fc / Fc+ in dichloromethane solution at room temperature. negative), which is less negative than about -1.00V.

[0065] In further embodiments, the n-type dopant is a molecular dopant having a first oxidation potential that is more negative than about −0.40 V and less negative than about −0.70 V when measured under the same conditions by cyclic voltammetry versus Fc / Fc+ in dichloromethane solution at room temperature.

[0066] In a further embodiment, the n-type dopant is a metal compound selected from the group of metal halides having a molecular weight of about 25 to about 250.

[0067] In a further embodiment, the n-type dopant is a metal complex having a molecular weight of about 150 to about 1000.

[0068] In another embodiment, the n-type dopant may be one of the alkali halides and metal complexes selected from the group of alkali metal organic complexes, main group, and paddlewheel complexes of transition metals.

[0069] In a further embodiment, the n-type dopant is a zero-valent metal selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Eu, Yb, and Sm, preferably Li, Na, Cs, Mg, Sr, Eu, Yb, and Sm.

[0070] The p-type and n-type dopants referred to herein are non-emissive in nature.

[0071] (light absorbing layer) The light-absorbing layer according to the present disclosure includes at least one absorber compound. The absorber compound may have a stoichiometry of AMX3 or A2MX4. "A" and "M" are cations, and "X" is an anion. The cations "A" and "M" can have various charges. In the original perovskite mineral (CaTiO3), cation A is divalent and cation M is tetravalent. The term "perovskite" as used herein means "perovskite crystal structure" but is not limited to the specific structure of the perovskite material, CaTiO3. "Perovskite" can include any material with the same type of crystal structure as calcium titanium oxide, as well as materials in which divalent cations are replaced by two distinct monovalent cations. The perovskite formula used herein can include structures with three or four anions (which may be the same or different), one or two organic cations, and / or two or three metal atoms carrying positive charges. Organic-inorganic perovskites are hybrid materials that combine the properties of organic complexity with inorganic crystallinity. The inorganic components form a framework bound by covalent bonds and ionic interactions, providing high carrier mobility. The organic component aids in the self-assembly process of these materials. Also, hybrid materials can be deposited by low-cost techniques, similar to other organic materials. An additional important property of the organic component is tuning the electronic properties of the organic-inorganic material by reducing the dimensions between them and providing electronic coupling between the inorganic sheets.

[0072] In another embodiment, A is a monovalent or divalent cation. In another embodiment, A is selected from the group of monovalent or divalent ammonium cation, monovalent or divalent alkali metal cation, and monovalent or divalent alkaline earth metal cation.

[0073] In further embodiments, A is independently selected from an organic monovalent cation selected from primary, secondary, tertiary, or quaternary organoammonium compounds (containing N-containing heteroaryl rings and ring systems), where A has 1 to 60 carbon atoms and 1 to 20 heteroatoms; or A is an organic divalent cation selected from primary, secondary, tertiary, or quaternary organoammonium compounds, where A has 1 to 60 carbon atoms and 2 to 20 heteroatoms and has two positively charged nitrogen atoms; or A is selected from the group of alkali metals and / or alkaline earth metals.

[0074] In another embodiment, A is a methylammonium (MA) cation [(CH3)3N] + or alkali metal cations, or a combination thereof.

[0075] In one embodiment, M is a divalent metal cation or a trivalent metal cation. In another embodiment, M is Cu 2+ , Ni 2+ , Co 2+ , Fe 2+ , Mn 2+ , Cr 2+ , Pd 2+ , Cd 2+ , Ge 2+ , Sn 2+ , Pb 2+ ,EU 2+ , or Yb 2+ or M is a divalent metal cation selected from the group consisting of Bi 3+ and Sb 3+ In yet a further embodiment, M is a trivalent metal cation selected from the group consisting of Pd 2+ , Sn 2+ is selected from the group consisting of:

[0076] In one embodiment, X is a monovalent anion. In another embodiment, X is Cl. - , Br - , I - , N.C.S. - , C.N. -, and N.C.O. - In a further embodiment, X is independently selected from I - , Cl - , and Br - is selected from.

[0077] (further layers) Further layers, especially those comprising charge transport materials (especially hole transport materials or electron transport materials), may be included in one or more layer stacks of the solar cells of the present invention.

[0078] The hole transport material can be triarylamine, carbazole, thiophene, phthalocyanine, diphenylhydrazone and quinoxaline. Further suitable hole transport materials are inorganic hole transport materials, such as MoX, V2O5.

[0079] Suitable electron transport materials according to the present invention are, for example, C 60 These include fullerenes, BCPs, and compounds containing a moiety selected from triazines, pyrazines, pyrimidines, acridines, benzoacridines, dibenzoacridines, phenanthrolines, benzimidazoles, carbazoles, anthracenes, fluorenes, spirofluorenes, phenanthrene, cyclic carboxylic acid imides, compounds containing large anellated aromatic hydrocarbon ring systems having more than 14 carbon atoms in the inorganic aromatic hydrocarbon ring system, and truxenes.

[0080] A method for determining the ionization potential (IP) is ultraviolet photospectroscopy (UPS). While it is common to measure the ionization potential of solid materials, it is also possible to measure IP in the gas phase. Both values ​​are distinguished by their solid-state effect, which is, for example, the polarization energy of the holes generated during the photoionization process. A typical value for the polarization energy is about 1 eV, but values ​​can vary significantly. The IP is related to the onset of the photoemission spectrum, which is the region with the highest kinetic energy for the photoelectrons (i.e., the region where the electrons are most weakly bound). Inverted photoelectron spectroscopy (IPES), a method related to UPS, can be used to determine the electron affinity (EA), but this method is less common. Electrochemical measurements in solution can also be used to determine the solid-state oxidation potential (E ox ) and solid-state reduction potential (E red ) measurement. A suitable method is, for example, cyclic voltammetry. To avoid confusion, the claimed energy levels are defined relative to a reference compound that has a well-defined redox potential in cyclic voltammetry when measured by standardized procedures. To convert redox potentials to electron affinities and ionization potentials, a simple rule is very often used: IP (in eV) = 4.8 eV + e * E ox (E ox is ferrocenium / ferrocene (Fc + / Fc), and EA (unit: eV) = 4.8 eV + e * E red (E red is Fc + / Fc) (Reference: B.W. D'Andrade, Org. Electron. 6, 11-20 (2005)). e *is the charge of the element. Conversion factors for the recalculation of the electrochemical potential at other reference electrodes or other reference redox couples are known (see AJ Bard, LR Faulkner, "Electrochemical Methods: Fundamentals and Applications", Wiley, 2. Ausgabe 2000). Information on the influence of the solution used can be found in NG Connelly et al., Chem. Rev. 96, 877 (1996). The "energy of the HOMO", E, is sometimes used as a synonym for the ionization energy, even if it is not exact. (HOMO) , "LUMO energy" E as a synonym for electron affinity (LUMO) It is customary to use the term IP=-E (Koopmans Theorem). It must be taken into account that it is usually reported that the larger the value of the ionization potential, the stronger the binding of the released electron, and the larger the value of the electron affinity, the stronger the binding of the absorbed electron. The energy scale of the frontier molecular orbitals (HOMO, LUMO) is opposite to this. Therefore, as a rough approximation, the following formula is valid: IP=-E (HOMO) and EA=E (LUMO) (The zero energy state is assigned to the reduced pressure).

[0081] For certain materials, such as hole transport materials, the ionization potential of the material may be greater than 5.30 eV.

[0082] If the solar cell includes two or more stacks, the different layer stacks can be separated from one another and can be connected to one another by an interconnection layer. The interconnection layer is disposed between the first electrode and the second electrode, between the first layer stack and the second layer stack, and in direct contact with both layer stacks. Respective intermediate layers and materials for forming the intermediate layers are known from the prior art, for example, WO2007 / 071451 A1, WO08 / 077615 A1, or WO2010 / 132236 A1.

[0083] (electrode) In one embodiment, the first electrode of the solar cell device is transparent and the solar cell is illuminated through the first electrode, while in another embodiment, the second electrode of the solar cell device is transparent and the solar cell is illuminated through the second electrode.

[0084] In a further embodiment, the material of the transparent electrode is a thin conductive oxide (TCO).

[0085] In another embodiment, the transparent electrode material is selected from the group consisting of indium-tin-oxide (ITO), aluminum-zinc-oxide (AZO), indium-gallium-zinc-oxide (IGZO), indium-zink-oxide (IZO), zinc molybdate (MZO) and indium-molybdenum-oxide (IMO).

[0086] In another embodiment, the transparent electrode material is selected from the group of magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag), silver (Ag), gold (Ag), and the like.

[0087] In one embodiment, the first electrode is a cathode and the second electrode is an anode.

[0088] (definition) As used herein, the following defined terms shall be applied unless a different definition is given in the claims or elsewhere in this specification.

[0089] In the context of this specification, the term "room temperature" refers to a temperature of about 20 to about 25°C, preferably about 22°C.

[0090] Cyclic voltammetry (CV) is an electrochemical technique that measures the current generated in an electrochemical cell under conditions where the voltage exceeds that predicted by the Nernst equation for a given compound. CV is performed by cycling the potential of the working electrode and measuring the resulting current.

[0091] Cyclic voltammetry is used to determine the first oxidation potential and first reduction potential.

[0092] The first oxidation potential is the potential at which the compound under investigation loses one electron.

[0093] The first reduction potential is the potential at which the compound under investigation gains one electron.

[0094] In one embodiment, the organic p-type dopant is F6-TCNNQ, whose first reduction potential is about 0.25 V when measured under the same conditions by cyclic voltammetry versus Fc / Fc+ in acetonitrile solution at room temperature.

[0095] In one embodiment, the n-type dopant is the organic n-type dopant PhIm (N1,N4-bis(tri-p-tolylphosphoranylidene)benzene-1,4-diamine), whose first oxidation potential is about −0.46 V when measured under the same conditions by cyclic voltammetry vs. Fc / Fc+ in dichloromethane solution at room temperature.

[0096] In one embodiment, the light-absorbing layer comprises an absorber compound of formula CH3NH3PbI3, which has a first oxidation potential comparable to that of TaTm when measured under the same conditions by cyclic voltammetry versus Fc / Fc+ in dichloromethane solution at room temperature.

[0097] As used herein, "weight % (wt%)" stands for weight percent.

[0098] As used herein, "mol %" stands for mole percent.

[0099] In this specification, all numerical values, whether explicitly stated or not, are assumed to be prefixed with "about." As used herein, the term "about" refers to possible variations in quantity. Whether modified by the term "about," the claims include equivalents to the quantities.

[0100] It should be noted that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise.

[0101] The expression "free" means that impurities are not included. Impurities have no technical effect with respect to the objectives achieved by the present disclosure.

[0102] The term "molecular weight" is a physical property defined as the mass of a given substance (chemical element or compound) divided by the molar amount (number of moles) of the substance. The base SI unit of molecular weight is kg / mol. For historical reasons, molecular weight is almost always expressed in g / mol. Molecular weight can be calculated from the standard atomic mass, which is the sum of all standard atomic masses in a compound. Standard atomic masses are shown in the periodic table of the elements. Experimentally, molecular weight can be determined by mass spectrometry, from vapor density, freezing point depression, or boiling point elevation.

[0103] The phrase "essentially non-luminescent" means that the visible emission spectrum of a particular compound is "essentially non-luminescent" and has a wavelength range of less than 10%, preferably less than 5%, and more preferably less than 1% of the visible emission spectrum. The visible emission spectrum is the emission spectrum within the wavelength range of about 380 nm to about 780 nm.

[0104] A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electrical energy through the physical and chemical phenomenon of the photovoltaic effect.

[0105] According to another aspect of the present disclosure, there is provided a method for manufacturing a solar cell using deposition by vacuum thermal evaporation.

[0106] Solar cells are often referred to in the art as pin or nip devices. The present invention describes so-called pii or nii devices. The terms "pin," "nip," "nii," and "pii" are shorthand for describing the arrangement of layers in at least one layer stack. "p" refers to a layer that contains or consists of a p-type dopant. "n" refers to a layer that contains or consists of an n-type dopant. "i" stands for "intrinsic" and refers to a layer that does not contain or consist of either a p-type or n-type dopant.

[0107] [Description of the embodiment] Further aspects are disclosed below by reference to the figures, in which:

[0108] FIG. 1a is a schematic diagram of a prior art solar cell with a pin layer sequence; FIG. 1b is a schematic diagram of a prior art solar cell with nip layer sequence; Figure 2 is a schematic diagram of a solar cell with p-i layer order, Figure 3 is a schematic diagram of a solar cell in layer order; Figure 4 is a schematic diagram of a solar cell with the n-i layer order, Figure 5 is a schematic diagram of a solar cell with an iip layer order; FIG. 6 is a schematic diagram of a solar cell comprising a first layer stack and a second layer stack; FIG. 7 is a schematic diagram of a solar cell with more than two different layer stacks; FIG. 8 is a schematic diagram of a solar cell comprising more than two different layer stacks interconnected by an interconnect layer.

[0109] 1a and 1b show prior art solar cells with p-i-n layer sequences. Referring to FIG. 1a, the solar cell includes a first electrode 120 and a second electrode 140. A light-absorbing layer 100 is disposed between the first electrode 120 and the second electrode 140. The light-absorbing layer includes an absorber compound with a perovskite crystal structure. The absorber compound may have a stoichiometry of AMX3, where "A" and "M" are cations and "X" is an anion. The first electrode 120 and the second electrode 140 form an anode and a cathode. This allows for the provision of n-i-p and p-i-n devices.

[0110] 2 shows a schematic diagram of a solar cell with a p-i layer order according to the present invention. The solar cell includes a layer stack between a first electrode 120 and a second electrode 140, comprising a first hole transport layer (HTL) 150, a p-type dopant layer 180, a second hole transport layer 160, a light absorbing layer 100, and an electron transport layer (ETL) 170 (together forming a layer stack). The p-type dopant layer 180 is provided between the first electrode 120 and the light absorbing layer 110. No n-type dopant layer is provided between the light absorbing layer 100 and the second electrode 140.

[0111] 3 shows another solar cell in layer order. In this embodiment, a layer stack formed by a first hole transport layer 150, a light absorbing layer 100, a first electron transport layer 170, an n-type dopant layer 190, and a second electron transport layer 200 is disposed between a first electrode 120 and a second electrode 140. In this embodiment, an n-type dopant layer (composed of one or more n-type dopant materials) is disposed between the light absorbing layer 100 and the second electrode 140. In this embodiment, no p-type dopant layer is formed between the light absorbing layer 100 and the first electrode 120.

[0112] 4 shows a schematic diagram of a solar cell with a layer order of 11. The solar cell includes a layer stack including a first electron transport layer 170, an n-type dopant layer 190, a second electron transport layer 200, a light absorbing layer 100, and a first hole transport layer 150. The layer stack is disposed between a first electrode 120 and a second electrode 140. In this embodiment, the n-type dopant layer 190 is formed between the light absorbing layer 100 and the first electrode 120. In this embodiment, no p-type dopant layer is formed between the light absorbing layer 100 and the second electrode 140.

[0113] 5 shows a further schematic diagram of an embodiment of a solar cell with an iip layer order. Again, the layer stack is disposed between a first electrode 120 and a second electrode 140. The layer stack in this embodiment is formed by a first electron transport layer 170, a light absorbing layer 100, a first hole transport layer 150, a p-type dopant layer 180, and a second hole transport layer 160. The p-type dopant layer 180 is disposed between the light absorbing layer 100 and the second electrode 140. In this embodiment, no n-type dopant layer is formed between the light absorbing layer 100 and the first electrode 120.

[0114] 6 shows a further embodiment of the invention in which a solar cell comprises two different layer stacks 210 and 220. The first layer stack 210 is disposed between and in contact with the first electrode 120 and the second layer stack 220. The second layer stack 220 is disposed between and in contact with the first layer stack 210 and the second electrode 140.

[0115] Figure 7 shows a schematic diagram of a solar cell including three or more layer stacks. In this embodiment, various different layer stacks 210, 220, 230 are disposed between a first electrode 120 and a second electrode 140, and the layer stacks 210, 220, 230 are in contact with each other and with the electrodes. Each of the layer stacks 210, 220, 230 shown in Figures 6 and 7 may be a layer stack such as that shown in any of Figures 2-5.

[0116] Figure 8 shows a special embodiment of the solar cell shown in Figure 7. In addition to the elements shown in Figure 7, the solar cell according to Figure 8 includes a first interconnect layer 240 connecting the first layer stack 210 and the second layer stack 220, and a second interconnect layer 250 connecting the second layer stack 220 and the third layer stack 230.

[0117] (Example) Below, experimental results for different embodiments of the solar cell shown in the figures are described.

[0118] (General procedure for the fabrication of vacuum-processed perovskite solar cells) Solar cell 1 (pii type) and solar cell 2 (nii type) were produced as follows.

[0119] The ITO-coated glass substrate was patterned by photolithography to limit the active area of ​​the solar cell and allow easy contact with the top electrode. The materials used were the p-type dopant 2,2'-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6-TCNNQ), the hole transport material N4,N4,N4'',N4''-tetra([1,1'-biphenyl]-4-yl)-[1,1':4',1''-terphenyl]-4,4''-diamine (TaTm), and the n-type dopant N1,N4-bis(tri-p-tolylphosphoranylidene)benzene-1,4-diamine (PhIm). The electron transport material was fullerene (C 60 The precursor materials for the perovskite light absorbing layer are PbI2 and CH3NH3I (MAI).

[0120] For characterization of the fabricated embodiments, grazing incident X-ray diffraction (GIXRD) patterns were collected at room temperature on an Empyrean PANanalytical powder diffractometer using Cu Kα radiation. Typically, three consecutive measurements were collected and averaged into a single spectrum. The surface morphology of the thin films was analyzed using an atomic force microscope (AFM, Multimode SPM, Veeco, USA). Scanning electron microscopy (SEM) images were performed on platinum-metallized samples with a Hitachi S-4800 microscope operating at an accelerating voltage of 2 kV. Absorption spectra were collected using a fiber-optic-based Avantes Avaspec2048 spectrometer.

[0121] The solar cells were characterized as follows: The external quantum efficiency (EQE) was estimated using the cell response at different wavelengths (measured with a white light halogen lamp combined with a bandpass filter). The solar spectrum mismatch was corrected using a calibrated silicon reference cell (MiniSun simulator by ECN, The Netherlands).

[0122] Current density-voltage (JV) characteristics were obtained under white light illumination using a Keithley 2400 light source measurement unit. The short-circuit current density was corrected taking into account the EQE of the device. Electrical characteristics were confirmed using a solar simulator from Abet Technologies (Model 10500 with an AM1.5G xenon lamp as the light source). Before each measurement, the exact light intensity was determined using a calibrated Si reference diode with an infrared cutoff filter (KG-3, Schott). JV curves were recorded between -0.2 and 1.2 V in 0.01 V steps, and the signal was integrated for 20 ms after a 10 ms delay. This resulted in a 20 ms signal with a resolution of approximately 0.3 Vs. -1 corresponds to a speed of

[0123] The device layout used to construct the solar cell is 0.01cm 2 Four equal pixels (0.06 cm) measured through a shadow mask with an opening of 2 The area of ​​the patterned ITO is defined as the overlap between the patterned ITO and the top metal contact. To investigate the hysteresis, different scan rates (0.1, 0.5, and 1 Vs) were used. -1 The device was biased from -0.2 to 1.2 V in 0.01 V steps with a 1000 V power supply (Voltage Intensity ...

[0124] Further, for device preparation, the ITO-coated glass substrates were subsequently cleaned with soap, water, and isopropanol in an ultrasonic bath, followed by UV-ozone treatment. They were transferred to a vacuum chamber built into a nitrogen-filled glove box (MBraun, H2O and O2 < 0.1 ppm) and 1 × 10 -6 The chamber was evacuated to a pressure of 10 ...

[0125] For thickness calibration, first, the materials TaTm, F6-TCNNQ, C 60 and PhIm were sublimated individually. Calibration factors were obtained by comparing the thickness estimated from the QCM sensor with the thickness measured with a mechanical profilometer (Ambios XP1). These materials were then sublimated from 135°C for Comparative Examples 1 and 2, and 160°C for the dopants TaTm and C. 60were co-sublimed at temperatures ranging up to 250 °C. The deposition rate was controlled and adjusted by separate QCM sensors to obtain the desired doping concentration. Generally, Ta, Tm, and C 60 The deposition rate of the dopant during codeposition was varied from 0.8 Å s -1 The pure dopant (F6-TCNNQ and PhIm) layers (for solar cells 1 and 2) and the undoped TaTm and C 60 The layer (for all examples in Table 2) is 0.5 Ås -1 It was deposited at a rate of

[0126] Once deposition on ITO was complete, the chamber was vented with dry N2 and the crucible was replaced with a crucible containing the precursor materials for the perovskite absorber layer deposition, PbI2 and CH3NH3I. The vacuum chamber was then cooled to 100°C. -6 The pressure was then evacuated again to 1000 mbar, after which a perovskite film (light-absorbing layer) was obtained by co-deposition of these two precursors.

[0127] Calibration of the CH3NH3I deposition rate is difficult due to the layer non-uniformity and material flexibility, which prevent accurate thickness measurements. Therefore, the CH3NH3I source temperature was kept constant at 70 °C, and the CH3NH3I:PbI2 ratio was controlled offline using grazing incidence X-ray diffraction by adjusting the PbI2 deposition temperature. The optimal deposition temperatures are 250 °C for PbI2 and 70 °C for CH3NH3I. After depositing a 500 nm thick perovskite film, the chamber was vented and the crucible was placed in a C 60 and replaced with one containing PhIm. -6 The crucible was then evacuated again to a pressure of 0.5 mbar. This process of exchanging the crucibles was carried out to minimize possible cross-contamination between the organic material and the perovskite precursor.

[0128] The solar cell device of Comparative Example 1 was prepared using pure C 60 films of and n-type doped C 60 Layer(C 60The solar cell 1 was further processed by depositing a 25 nm thick film of C 60 The deposition of the MoO3 layer was performed in 0.5 Å s. -1 The deposition rate was 0.015 g / cm 2 , and the deposition was carried out in a vacuum chamber separate from the alumina-coated aluminum crucible.

[0129] Five substrates (3 × 3 cm) were prepared in one deposition run. Each substrate contained four cells. Typically, one substrate was kept as a reference structure. Finally, the substrates were transferred to a second vacuum chamber where metal electrodes (100 nm thick) were deposited. For the nip and nii devices, the same procedure as described above was used, but in reverse order.

[0130] The layer stack details are shown in Table 4.

[0131] The details of the layer stack in a solar cell device are shown below: A slash " / " indicates the separation of individual layers. Layer thicknesses are enclosed in square brackets [...].

[0132] [Technical Effects of the Present Invention] Solar cell devices according to the present invention have demonstrated improved efficiency and lifetime when compared to prior art solar cells.

[0133] [Table 3]

[0134] [Table 4]

[0135] [Table 5]

[0136] To compare the performance of different solar cells, four parameters are selected, defined as follows (source: www.pveducation.org): 1) Open circuit voltage (Voc) (unit: mV) - The maximum voltage available from a solar cell. This voltage occurs when there is zero current. 2) Short-circuit current (Jsc) (unit: mA cm -2 )—The current that flows through a solar cell when the voltage applied to the solar cell is zero (i.e., the solar cell is short-circuited). This current is the maximum current that can be drawn from the solar cell. 3) At both of these operating points (i.e., Voc and Jsc), the power from the solar cell is zero. The "fill factor" (FF) (unit: %) is a parameter that determines the maximum power from the solar cell in relation to Voc and Isc. FF is defined as the ratio of the maximum power from the solar cell to the product of Voc and Isc. Graphically, FF is a measure of the "squareness" of the solar cell. FF is also the area of ​​the largest rectangle that can be fitted to the IV curve. 4) Power Conversion Efficiency (PCE) (unit: %) - The ratio of the energy output from the solar cell to the energy input from the sun. PCE = Voc * Jsc * FF.

[0137] The features disclosed in the specification, drawings, and / or claims may be materials for the realization of various embodiments, selected singly or in various combinations of multiple features. [Brief explanation of the drawings]

[0138] [Figure 1a] FIG. 1 is a schematic diagram of a prior art solar cell with a pin layer sequence. [Figure 1b] 1 is a schematic diagram of a prior art solar cell with nip layer sequence; [Figure 2]Schematic diagram of a solar cell in pii layer order. [Figure 3] Schematic diagram of a solar cell in layer order. [Figure 4] Schematic diagram of a solar cell with n-i layer order. [Figure 5] Schematic diagram of a solar cell with iip layer order. [Figure 6] 1 is a schematic diagram of a solar cell comprising a first layer stack and a second layer stack. [Figure 7] FIG. 1 is a schematic diagram of a solar cell with more than two different layer stacks. [Figure 8] FIG. 1 is a schematic diagram of a solar cell comprising more than two different layer stacks interconnected by an interconnect layer.

Claims

1. A solar cell, a) a first electrode; b) a second electrode; and c) a layer stack disposed between the first electrode and the second electrode, The layer stack is: (c1) one light absorbing layer having a perovskite crystal structure; (c2) at least one dopant layer; The at least one dopant layer comprises: (i) one or more n-type dopant materials, or (ii) one or more p-type dopant materials; A solar cell consisting of:

2. The solar cell of claim 1 , wherein the at least one dopant layer is disposed between the first electrode and the light absorbing layer.

3. The solar cell of claim 1 , wherein the at least one dopant layer is disposed between the second electrode and the light absorbing layer.

4. The solar cell is two or more layer stacks; and optionally at least one interconnect layer; The solar cell according to claim 1 , wherein the interconnect layer is disposed between two different layer stacks.

5. the p-type dopant material is an organic compound, a metal organic compound, or an organometallic compound; 5. The solar cell according to claim 1, wherein the total amount of electron-withdrawing groups in the organic compound is from 17 atomic percent to 90 atomic percent.

6. 6. The solar cell of claim 1, wherein the n-type dopant material is selected from the group consisting of metals, metal salts, metal complexes, and mixtures thereof.

7. 7. The solar cell of claim 6, wherein the metal is selected from the group consisting of alkali metals, alkaline earth metals, transition metals, rare earth metals, and mixtures thereof.

8. The above metals are selected from Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Sm, Eu, and Yb; The solar cell according to claim 7, wherein the element is more preferably selected from the group consisting of Li, Na, Cs, Mg, Sr, Yb, Eu, and Sm.

9. 7. The solar cell of claim 6, wherein the metal salt is selected from the group consisting of alkali metal salts, alkaline earth metal salts, rare earth metal salts, and mixtures thereof.

10. The alkali metal salt is selected from the group consisting of LiF, LiCl, LiBr, LiI, and mixtures thereof; or, The solar cell according to claim 9 , wherein the alkali metal salt is LiF.

11. The solar cell according to claim 6 , wherein the metal complex is an organic alkali metal complex.

12. 12. The solar cell according to claim 1, wherein the dopant layer has a thickness of from 0.1 to 25 nm.

13. The solar cell of claim 1 , wherein the dopant layer is a self-assembled monolayer.

14. A solar panel comprising the solar cell according to any one of claims 1 to 13.

Images