Photovoltaic device

Abstract

To address the issue of a conventional PIN structure.SOLUTION: A photovoltaic device has a PIN structure, a p-type hole transport layer (2) is carried by a substrate (1), and a perovskite layer (3) and an n-type electron transport layer (4) are arranged in sequence on the p-type layer. A light transmissive electrically conductive layer (9) is provided on top of the n-type electron transport layer to form a light receiving top surface. Between the n-type electron transport layer and the light transmissive conductive layer, there are provided two inorganic electrically insulative layers (6, 8) having a layer of a conductive material (7) therebetween. The two inorganic electrically insulative layers include a material having a band gap of greater than 4.5 eV, and the layer of a conductive material includes a material having a band gap of less than the band gap of the electrically insulative layers. Each electrically insulative layer forms a type-1 offset junction with the layer of conductive material.SELECTED DRAWING: Figure 1B

Description

Technical Field

[0001] The present application relates to a photovoltaic (PV) device, and more particularly to a multi-junction photovoltaic device such as a perovskite PV device and a tandem solar cell having a perovskite-based sub-cell.

Background Art

[0002] Solar energy is one of the most promising technologies for providing renewable energy. Historically, however, the high cost of manufacturing devices for obtaining solar energy, including high material costs, has hindered its widespread adoption.

[0003] For example, a single-junction solar cell, such as a single-junction solar cell composed of a silicon p-n junction, has a maximum theoretical efficiency of about 29% under AM1.5G conditions (see, for example, A. Reinders et al., "Perovskite Solar Energy - From Fundamentals to Applications", Wiley, ISBN 9781118927465

[2017] , p164), and the practical efficiency is at most 26%. However, when cells made of materials with a higher bandgap are stacked on a silicon single-junction cell (or another type of single-junction cell) and connected in series, the limiting theoretical efficiency increases to exceed 40%. Therefore, there is great interest in tandem and other multi-junction cell technologies.

[0004] Also, single-junction perovskite solar cells show efficiencies comparable to those of silicon.

[0005] A solar cell can have a typical structure or an inverted structure. In the case of an inverted perovskite solar cell as described in the present application, it is often developed in a configuration referred to as P-I-N (a continuous layer of p-type contact (P), perovskite (I), and n-type contact (N)), and usually, an organic n-contact is used for this. However, this organic material can deteriorate during the continuous layer formation process. This problem can be particularly severe, for example, when the subsequent TCO (transparent conductive oxide electrode) layer is coated by sputtering onto the n-type contact. To protect the organic n-contact layer from sputter damage during the sputtering of subsequent material layers, a dense n-type inorganic contact can be formed immediately after the deposition of the organic n-contact layer.

[0006] For example, in an inverted PIN perovskite solar cell, the use of atomic layer deposition (ALD)-grown n-type SnO2 has been proposed for electron selection and sputter protection of the organic fullerene contact (Bush et al., 2017 (10.1038 / nenergy.2017.9)). Also, on June 11, 2018, an online publication by Sahli et al. in Nature Materials (https: / / doi.org / 10.1038 / s41563-018-0115-4) disclosed a fully textured monolithic perovskite / silicon tandem solar cell. By the atomic layer deposition method, a buffer layer of SnO2 is deposited on the stack. A review on the use of ALD in perovskite solar cells has been recently published - see V. Zardetto, B. L. Williams et al., Sustainable Energy & Fuels, vol. 1, p30-55 (2017). The inverted PIN perovskite device structure is described in more detail in "Organic-Inorganic Halide Perovskite Photovoltaics" edited by Park, Gratzel, Miyasaka, Springer (2016) ISBN 978-3-319-35112-4 (see especially Chapter 12, p307-p324).

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, existing technologies have many potential drawbacks as follows: 1) Process reproducibility: Due to the surface dependence of nucleation in many ALD processes, the film thickness can vary from run to run. In the case of SnO2, this can be up to 10 to 15%. 2) Carrier recombination at the inorganic-n / fullerene interface due to unpassivated bonds results in losses in the open-circuit voltage (V OC ) and fill factor (FF) in the solar cell device. 3) The purpose of the inorganic n-type layer is to protect the organic n-type layer and the perovskite layer from sputter damage and to suppress the formation of regions of harmful ITO / organic n contacts and ITO / perovskite contacts. Insufficient density and / or surface coverage of the inorganic layer, or overly high conductivity, can limit this effect.

[0008] The object of the present invention is to address these conventional problems.

Means for Solving the Problems

[0009] In a first aspect of the present invention, a photovoltaic device defined in claims 1 to 11 is provided.

[0010] A photovoltaic device having a multi-layer interface layer is known from US Patent No. 9,416,279. However, this patent shows a typical NIP structure rather than the PIN structure of the present invention. The manufacturing process considerations faced by the NIP structure and the PIN structure are different. Usually, sputtering has few problems in the NIP structure, but the use of sputtering for the PIN structure can damage the material as described above. The present invention relates to an inverted perovskite solar cell and provides an inorganic “intrinsic-n-type-intrinsic (INI)” sandwich structure to replace the well-ordered inorganic n-type layer of the prior art. Compared with the case of using the three-layer stack of the present invention, when using a single “well-ordered” SnO2 layer, the variation becomes larger and the peak and average efficiency become lower.

[0011] The use of the three - layer interface structure of the present invention is significant for several reasons compared to using a single SnO2 layer. In the stack, by using a first electrical insulating layer, such as Al2O3, when using ALD, highly reproducible growth throughout the stack becomes possible. The growth of ALD depends almost entirely on surface chemistry. The Al2O3 layer functions as a rapid nucleation layer, and the surface is functionalized by the formation of OH surface termination. This promotes the growth of the next layer in the stack. Finally, the inclusion of the first layer suppresses the variation in the thickness of the Lanz - to - Lanz.

[0012] Also, the first layer (e.g., Al2O3) can function to chemically passivate any free bonds present at the inorganic - n / organic - n interface. Subsequently, the density of electron traps available for carrier recombination is reduced, and thus, the saturation current density and the ideality factor of the diode are reduced. This can function to increase both the open - circuit voltage and the fill factor.

[0013] Finally, a material such as Al2O3 can function as a reservoir of free radicals. By providing additional protection from sputter damage and preventing ITO / organic - n or ITO / perovskite defect interfaces, the formation of parasitic shunt paths and / or weak diode regions can be suppressed.

[0014] In a second aspect of the present invention, a method for manufacturing a photovoltaic device according to any one of claims 1 to 11 is provided. By atomic layer deposition, two inorganic electrical insulating layers and a layer of a conductive material therebetween are sequentially deposited on a layer of an n - type electron transport material. Such deposition is preferably performed at a temperature of 125 °C or lower.

[0015] Hereinafter, embodiments of the present invention will be described with reference to the attached schematic diagrams. The embodiments of the present invention are described merely as an example.

Brief Description of the Drawings

[0016]

Figure 1A

Figure 1B

Figure 2

Figure 3

Figure 4

Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0017] In one embodiment, the perovskite device has a PIN structure, with a p-type hole transport layer disposed (or supported) on a substrate, a perovskite layer and an n-type electron transport layer disposed in this order on the p-type layer, a light-transmissive conductive layer provided on top of the n-type electron transport layer, and a light-receiving upper surface formed. An interface structure is provided between the n-type electron transport layer and the light-transmissive conductive layer, which has two inorganic electrical insulating layers with a layer of conductive material therebetween. The two inorganic electrical insulating layers have a material with a bandgap greater than 4.5 eV, and the layer of conductive material has a material with a bandgap less than that of the electrical insulating layer (e.g., greater than 2 eV and 4.0 eV or less).

[0018] It is significant that the substrate has another photovoltaic sub-cell and a monolithically integrated multi-junction photovoltaic device is formed. This another photovoltaic sub-cell may have, for example, sub-cells of another perovskite, single-crystalline silicon, polysilicon, Cu(In,Ga)Se2, or Cu2ZnSn(S,Se)4.

[0019] The photovoltaic device is a monolithically integrated solar cell, and it is significant that the another sub-cell has a layer of perovskite material.

[0020] The perovskite material is preferably bipolar. Usually, this has a three-dimensional crystal structure with the general formula ABX3. Here, A includes one or more organic or inorganic cations (for example, methylammonium, formamidinium, guanidinium, etc., and cations such as cesium, rubidium, etc.), B represents a divalent metal selected from one or more of the group consisting of Pb, Sn, Sb, or Ti, and X represents one or more halide anions selected from, for example, Cl, Br, and I.

[0021] In another embodiment, a photovoltaic device is provided that has a pn junction of Cu(In,Ga)Se2 or Cu2ZnSn(S,Se)4 including a p-type layer and an n-type layer, and a light-transmissive conductive layer provided on the upper part of the n-type layer to form a light-receiving upper surface. A structure is provided that has two inorganic electrical insulation layers including a layer of conductive material between the n-type layer and the light-transmissive conductive layer. The two inorganic electrical insulation layers have a material with a bandgap larger than that of the conductive material (for example, greater than 4.5 eV), and the layer of conductive material has a material with a bandgap larger than 2 eV and smaller than that of the electrical insulation layer (for example, less than 4.0 eV).

[0022] Figure 1A schematically shows a cross-section of a conventional device stack. On the other hand, Figure 1B shows a schematic cross-section of a photovoltaic device according to the present invention. The substrate at the bottom of each stack (1) has a material such as glass having an upper TCO layer like ITO, or has a bottom sub-cell like a silicon solar cell. The perovskite / silicon tandem solar cell is shown in more detail, for example, by Werner et al., Adv. Mater. Interfaces 5, 1700731 (2017).

[0023] Figure 1B shows an embodiment according to the present invention. As shown in the figure, the bottom of the stack (1) has a Si bottom cell or ITO / glass. Next, this is covered by a p-type layer (2), which is then covered by a perovskite layer (3). The perovskite layer is covered by an organic n-type layer (4). The upper part of the stack is composed of an ITO layer (9). Between the ITO layer and the organic n-type layer, there is a new three-layer interface structure (6, 7, 8) of the present invention.

[0024] The p-type layer (2) has a hole transport material, which may be inorganic or organic. The upper part of the p-type layer is the perovskite layer (3), which has a three-dimensional crystal structure such as, for example, MAPbI3 or FA 0.8 :Cs 0.2 PbI2Br. The composition of the perovskite layer can be suitably selected for the desired bandgap of the photoactive layer.

[0025] The p-type layer is a layer of a hole transport (i.e., p-type) material. The 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, and these may be undoped or doped with one or more dopant elements.

[0026] The p-type layer may have an inorganic or organic p-type material. Usually, the p-type region has a layer of an organic p-type material.

[0027] Suitable p-type materials may be selected from polymer or molecular hole transporters. The p-type layer used in the photovoltaic device of the present invention may have, for example, 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) or tBP (tert-butylpyridine). The p-type region may have carbon nanotubes. Usually, the p-type material is selected from spiro OMeTAD, P3HT, PCPDTBT, and PVK. Preferably, the p-type region is composed of a p-type layer containing spiro OMeTAD.

[0028] The p-type layer may have, for example, 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]]), or PVK (poly(N-vinylcarbazole)).

[0029] Also, suitable p-type materials include molecular hole transporters, polymer hole transporters, and copolymer hole transporters. The p-type material may be, for example, a molecular hole transport material, a polymer or copolymer containing one or more of the following moieties: thiophenyl, phenylene, dithiazolyl, benzothiazolyl, diketopyrrolopyrrolyl, ethoxydithiophenyl, amino, triphenylamino, carbazolyl, ethylenedioxythiophenyl, Dioxythiophenyl or fluorenyl. Therefore, the p-type layer used in the photovoltaic device of the present invention may have, for example, any of the aforementioned molecular hole transport materials, polymers, or copolymers.

[0030] Also, suitable p-type materials include 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-(naphthalen-2-yl)-N-phenylamino)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), PEDOT:PSS, and Spiro-OMeTAD.

[0031] The p-type layer may be doped, for example, with tert-butylpyridine and LiTFSi. The p-type layer may be doped to increase the hole density. The p-type layer may be doped, for example, with NOBF4 (nitrosonium tetrafluoroborate) to increase the hole density.

[0032] In another example, the p-type layer may have an inorganic hole transporter. For example, the p-type layer may have an inorganic hole transporter including oxides of vanadium, copper, nickel, or molybdenum; CuI, CuBr, CuSCN, Cu2O, CuO, or CIS; perovskite; amorphous Si; p-type group-IV semiconductors, p-type group-III-V semiconductors, p-type group-II-VI semiconductors, p-type group-I-VII semiconductors, p-type group-IV-VI semiconductors, p-type group-V-VI semiconductors, and p-type group-II-V semiconductors. These may or may not be doped with an inorganic material. The p-type layer may be a dense layer of the inorganic hole transporter that is not porous.

[0033] The p-type layer may have an inorganic hole transporter including, for example, oxides of nickel, vanadium, copper, or molybdenum; CuI, CuBr, CuSCN, Cu2O, CuO, or CIS; amorphous Si; p-type group-IV semiconductors, p-type group-III-V semiconductors, p-type group-II-IV semiconductors, p-type group-I-VII semiconductors, p-type group-IV-VI semiconductors, p-type group-V-VI semiconductors, and p-type group-II-V semiconductors. These may or may not be doped with an inorganic material.

[0034] The p-type region may, for example, have a thickness of 5 nm to 100 nm. For example, the p-type region may have a thickness of 50 nm to 500 nm, or 100 nm to 500 nm. In the multi-junction photovoltaic device described above, the p-type region 112 of the first sub-cell preferably has a thickness of 10 nm to 50 nm, more preferably about 20 nm. Further, the p-type region may have a bilayer structure or a multilayer structure composed of two or more layers of different materials.

[0035] The perovskite material has the general formula (I) [A][B][X]3 (I) It may have. Here, [A] is one or more monovalent cations, [B] is one or more divalent inorganic cations, [X] is one or more halide anions, preferably having one or more halide anions selected from fluoride, chloride, bromide, and iodide, more preferably selected from chloride, bromide, and iodide. More preferably, [X] has one or more halide anions selected from bromide and iodide. In one example, [X] preferably has two different halide anions selected from fluoride, chloride, bromide, and iodide, more preferably selected from chloride, bromide, and iodide, and still more preferably having bromide and iodide.

[0036] [A] preferably has one or more organic cations selected from methylammonium (CH3NH3 + ), formamidinium (HC(NH)2)2 + ), and ethylammonium (CH3CH2NH3 + ), and preferably has one organic cation selected from methylammonium (CH3NH3 + ) and formamidinium (HC(NH)2)2 + ). [A] may have one or more inorganic cations selected from Cs + , Rb + , Cu + , Pd + , Pt + , Ag + , Au + , Rh + , and Ru + .

[0037] [B] has at least one divalent inorganic cation selected from Pb 2+ and Sn 2+ , and preferably has Pb 2+ .

[0038] In a preferred embodiment, the perovskite material has the general formula A x A’ 1-x B(X y X’ 1-y )3(IA) has. Here, A is formamidinium (FA), A’ is cesium cation (Cs + ), B is Pb 2+ , X is iodide, X’ is bromide, 0 < x ≦ 1 and 0 < y ≦ 1. Thus, in these preferred embodiments, the perovskite material can have a mixture of two monovalent cations. Also, in preferred embodiments, thus, the perovskite material can have either a single iodide anion, or a mixture of iodide anions and bromide anions. The inventors of the present application have found that such a perovskite material can have a band gap of 1.5 eV to 1.75 eV, and that a layer of such a perovskite material can be easily formed in a suitable crystalline form and phase. More preferably, the perovskite material is FA 1-x Cs x PbI 3-y Br y .

[0039] To provide a highly efficient photovoltaic device, ideally, it is necessary to maximize the absorption of the absorber and generate an optimal amount of current. As a result, when using perovskite as the absorber of a photovoltaic device or a sub-cell, in order to absorb most of the sunlight across the visible spectrum, the thickness of the perovskite layer should ideally be on the order of 300 to 600 nm. Therefore, usually, the thickness of the layer of perovskite material is greater than 100 nm. The thickness of the layer of perovskite material in a photovoltaic device may be, for example, from 100 nm to 1000 nm. The thickness of the layer of perovskite material in a photovoltaic device may be, for example, from 200 nm to 700 nm, and preferably from 300 nm to 600 nm. In the above-mentioned multi-junction photovoltaic device, the flat layer of perovskite material 11 in the photoactive region of the first / upper sub-cell 210 preferably has a thickness of 350 nm to 450 nm, and more preferably has a thickness of about 400 nm.

[0040] The perovskite layer may be prepared as described in WO2013 / 171517, WO2014 / 045021, WO2016 / 198889, WO2016 / 005758, WO2017 / 089819, the book "Photovoltaic Solar Energy: From Basics to Applications", edited by Angele Reinders, Pierre Verlinden, Wiley-Blackwell (2017) ISBN-13: 978-1118927465, and "Organic-Inorganic Halide Perovskite Photovoltaic Technology: From Basics to Device Structures", edited by Nam-Gyu Park et al., Springer (2016) ISBN-13: 978-3319351124.

[0041] On top of this perovskite layer, there is a layer of an electron transport material (4). The electron transport layer suitable for use in the perovskite photovoltaic cell in this embodiment is described in the recent review paper "Current Status of Electron Transport Layers in Perovskite Solar Cells: Materials and Properties", Mahmood, Sarwar and Mehran, RSCAdv. 2017.7.17044.

[0042] The electron transport layer usually includes an n-type region. In the multi-junction photovoltaic device described above, the n-type region of the first sub-cell has one or more n-type layers. Often, the n-type region is an n-type layer, i.e., a single n-type layer. However, in other examples, the n-type region may have an n-type layer and a separate n-type exciton blocking layer or hole blocking layer.

[0043] The exciton blocking layer is a material having a wider bandgap than the photoactive material, but either its conduction band or valence band is close to the photoactive material. When the conduction band (or the lowest unoccupied molecular orbital energy level) of the exciton blocking layer is arranged to approach the conduction band of the photoactive material, electrons enter the exciton blocking layer from the photoactive material or pass through the exciton blocking layer and enter the photoactive material. We refer to this as an n-type exciton blocking layer. Such an example is bathocuproine (BCP), which is described in P. Peumans, A. Yakimov, S. R. Forrest, “Small-Molecular-Weight Organic Thin-Film Photodetectors and Solar Cells,” J. Appl. Phys. 93, 3693 (2001), and Masaya Hirade, Chihaya Adachi, “Small-Molecular-Weight Organic Photovoltaic Cells with an Exciton Blocking Layer for Device Performance Improvement at the Anode Interface,” Appl. Phys. Lett. 99, 153302 (2011). as described in

[0044] The n-type layer (4) is a layer of an electron transport (i.e., n-type) material. The n-type material may be a single n-type compound or elemental material, or a mixture of two or more n-type compounds or elemental materials, which may be undoped or doped with one or more dopant elements.

[0045] The electron transport material used may have an inorganic or organic n-type material.

[0046] Suitable inorganic n-type materials may be selected from metal oxides, metal sulfides, metal selenides, metal tellurides, perovskites, amorphous or nanocrystalline Si, n-type group IV semiconductors, n-type III-V semiconductors, n-type II-VI semiconductors, n-type I-VII semiconductors, n-type IV-VI semiconductors, n-type V-VI semiconductors, and n-type II-V semiconductors. Any of these may or may not be doped.

[0047] More typically, the n-type material is selected from metal oxides, metal sulfides, metal selenides, and metal tellurides.

[0048] Accordingly, the n-type layer may have 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 the foregoing metals. For example, the n-type layer may have TiO2, SnO2, ZnO, Nb2O5, Ta2O5, WO3, W2O5, In2O3, Ga2O3, Nd2O3, PbO, or CdO.

[0049] Other suitable n-type materials that can be used include sulfides of cadmium, tin, copper, or zinc, and sulfides of a mixture of two or more of the foregoing metals. For example, the sulfide may have FeS2, CdS, ZnS, SnS, BiS, SbS, or Cu2ZnSnS4.

[0050] The n-type layer may have, for example, selenides of cadmium, zinc, indium, or gallium, or selenides of a mixture of two or more of the foregoing metals, or tellurides of cadmium, zinc, cadmium, or tin, or tellurides of a mixture of two or more of the foregoing metals. For example, the selenide may be Cu(In,Ga)Se2. Usually, the telluride is a telluride of cadmium, zinc, cadmium, or tin. For example, the telluride may be CdTe.

[0051] The n-type layer may have an inorganic material selected from, for example, oxides of titanium, tin, zinc, niobium, tantalum, tungsten, indium, gallium, neodymium, palladium, cadmium, or oxides of a mixture of two or more of said metals; sulfides of cadmium, tin, copper, zinc, or sulfides of a mixture of two or more of said metals; selenides of cadmium, zinc, indium, gallium, or selenides of a mixture of two or more of said metals; or tellurides of cadmium, zinc, cadmium or tin, or tellurides of a mixture of two or more of said metals.

[0052] Examples of other semiconductors that can be suitable n-type materials include, for example, group IV elements or compound semiconductors when they are n-doped; amorphous Si; III-V group semiconductors (such as gallium arsenide); II-VI group semiconductors (such as cadmium selenide); I-VII group semiconductors (such as cuprous chloride); IV-VI group semiconductors (such as lead selenide); V-VI group semiconductors (such as bismuth telluride); and II-V group semiconductors (such as cadmium arsenide).

[0053] When the n-type layer is an inorganic material, such as TiO2 or any of the other materials mentioned above, it is significant that this is a dense layer of said inorganic material. Preferably, the n-type layer is a dense layer of TiO2.

[0054] Other n-type materials may be used, including organic and polymeric electron transport materials and electrolytes. Suitable examples include, but are not limited to, organic electron transport materials containing fullerenes or fullerene derivatives, perylenes or their derivatives, or poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)}(P(NDI2OD-T2)). For example, the n-type region may have an n-type layer containing one or more of C60, C70, C84, C60-PCBM, C70-PCBM, C84-PCBM, and carbon nanotubes. This may have C60-IPB, C60-IPH, C70-IPB, C70IPH, or a mixture thereof. Such materials are commercially available from Solenne BV, Zernikepark 6, 9747AN Groningen, The Netherlands.

[0055] The n-type region can have a thickness from 3 nm to 1000 nm. When the n-type region includes a dense layer of n-type semiconductor, the dense layer has a thickness from 3 nm to 200 nm.

[0056] The interface structure (6, 7, 8) of the present invention has a conductive material (7) sandwiched between two electrical insulating layers (6, 8). The two electrical insulating layers have materials with a suitable bandgap greater than 4.5 eV. Each electrical insulating layer does not have to have the same material, but it is preferred that both layers have the same material. A wide bandgap is important. The material provides passivation of the bandgap states introduced by the underlying n-type region and the upper conductive layer (e.g., SnO2).

[0057] Figure 1B shows an example of the interface structure according to the present invention. On top of the n-type layer (4), two inorganic electrical insulating layers (6, 8) containing a material with a bandgap exceeding 4.5 eV and a layer of conductive material (7) therebetween are formed. The latter preferably has a material with a bandgap greater than 2 eV and less than 4.0 eV. The electrical insulating layers are preferably formed by atomic layer deposition (ALD).

[0058] As shown in FIG. 5, the layer of conductive material forms a straddle type 1 offset junction by each electrical insulation layer. In this figure, E g-A >W g-B E C-A >E C-B E V-A <E V-B The electrical insulation layers (6, 8) are formed from a material having a band gap exceeding 4.5 eV, preferably exceeding 5, 5.5, 6, 6.5 or 7 eV. Suitable materials include Al2O3 and LiF. The most preferred material is Al2O3.

[0059] The electrical insulation layer forms a barrier of the conduction band and valence band at the interface with the adjacent layer, and a type 1 heterojunction is generated at these positions.

[0060] Each layer of the electrical insulation material preferably has a thickness in the range of 0.1 to 10 nm, preferably in the range of 0.4 to 3 nm, and most preferably a thickness of about 1 nm.

[0061] The conductive layer 7 is formed from a material having a band gap smaller than the band gap of the material of the electrical insulation layers (6, 8). If each conductive layer is composed of different materials, the conductive layer is formed from a material having a band gap smaller than both materials. This is preferably greater than 2 eV and less than 4.0 eV. The conductive layer is preferably formed of a conductive n-type oxide. Suitable materials include SnO x ; ZnO x ; (Zn:Sn)O x ; TiO x and InO x are included. Most preferably, they are SnO2, ZnO, In2O3 and TiO2.

[0062] The most preferred material for the conductive layer is SnO2. The layer of the conductive material (7) between the two inorganic electrical insulating layers preferably has a thickness of 3 to 12 nm.

[0063] The bandgap is measured using UV-VIS spectroscopy using methods well known in the art. For example, if the bandgap is wider than that of the glass substrate, ellipsometry (extending sufficiently into the UV) can be used to make a more accurate determination of the parameter k. Next, the bandgap can be determined from the Tauc plot resulting from the k dispersion.

[0064] The bandgap can be measured as described in Chapter 3 of the paper by Vos et al., Journal of Vacuum Science & Technology, A34, 01A103 (2016).

[0065] Next, a light-transmissive conductive layer (9) is formed on top of the n-type electron transport layer to form a light-receiving upper surface. This layer typically has a sputtered transparent conductive oxide such as an ITO layer with a thickness of 10 to 200 nm, but alternatively or in addition, other oxides or materials such as metal nanowires can also be used. The selected thickness is determined by compromising between permeability and conductivity.

[0066] Hereinafter, the present invention will be described by way of examples.

[0067] (Example) Results for a PIN photovoltaic device having an inorganic "intrinsic-n-type-intrinsic (INI)" sandwich interface structure as shown in Figure 1B are shown. Here, the INI structure is specifically Al2O3 / SnO2 / Al2O3.

[0068] The Al2O3 layer has a thickness of 1 nm, the SnO2 layer has a thickness of 6 nm, and has SnO2 formed by ALD.

[0069] For the thermal ALD of Al2O3, the substrate is maintained at 80 to 120 °C. At room temperature, TMA and H2O are held in separate stainless steel containers, and the ALD sequence is TMA dose / TMA purge / H2O dose / H2O purge.

[0070] SnO x For the thermal ALD of SnO, the substrate is maintained at 80 to 120 °C. TDMASn and H2O are held in separate stainless steel containers at 60 °C and room temperature, respectively, and the ALD sequence is TDMASn dose / TDMASn purge / H2O dose / H2O purge.

[0071] The growth per unit cycle of the Al2O3 layer and the SnO2 layer is 0.1 - 0.12 nm and 0.12 - 0.14 nm, respectively, and the number of cycles is appropriately selected so that the desired thickness is achieved.

[0072] By thermal ALD, the entire stack is formed, and thickness control and film completion of each component of the stack are reliably carried out. H2O is used as a co-reactant in both the SnO2 and Al2O3 processes. TDMASn and TMA are used as the respective metal precursors. Next, A series of experiments were carried out on the stack of the present invention and a stack corresponding to the prior art. The latter was composed of a SnO2 layer instead of three layers. In other respects, both stacks were the same.

[0073] (Example 1: Measured thickness) Figure 2 is a plot of measured thickness normalized to the predicted thickness for the number of repeat runs, where a) is the case of SnO2 only and b) is the case of Al2O3 / SnO2 / Al2O3, and it is shown that the run-to-run variation is reduced in the three-layer compared to the single layer. This is due to the first Al2O3 layer, which acts to promote nucleation of the SnO2 layer.

[0074] Using spectroscopic ellipsometry, the thickness was measured from a Si observation sample included in the film formation run of the perovskite device. The measured thickness is relative to the nominal thickness, which is set by the number of ALD cycles used. The thickness was measured using a Woollam M2000 ellipsometer. A general oscillator model composed of a single Tauc-Lorentz oscillator was used to represent the complex dielectric function, and thereby, the raw psi-delta dispersion data was fitted. The fitting parameters extracted from the Tauc-Lorentz oscillator constitute the n and k dispersions. After data fitting, n at 632 nm was between 1.8 and 1.85.

[0075] (Example 2: Series resistance, ideality factor, reverse saturation current) Current-voltage (I-V) curves were constructed to evaluate the improved diode parameters when using the structure of the present invention. Measurements were made using a Keithley source meter. First, J-V curves were created and fitted to a single diode solar cell equivalent circuit to extract n (ideality factor), J0 (reverse saturation current), and Rs (series resistance). Voc, FF, etc. were obtained from AM1.5 of the illuminated J-V measurement.

[0076] Figure 3 is a table showing the ranges associated with the optimum values of series resistance, ideality factor, and reverse saturation current (from 20 single-junction perovskite devices for each device type) extracted by fitting a one-diode model to the dark current-voltage data. The gains in Voc and FF obtained using three layers instead of SnO2, measured from the photocurrent-voltage data, are also shown simultaneously.

[0077] The device parameters described in Figure 3, including both the ideality factor (n) and the saturation current (J0), are reduced by the introduction of the INI structure, indicating that recombination is decreased. The open-circuit voltage and FF are improved. When a logarithmic plot of the dark environment I-V curve was created, a decrease in the parasitic shunt current was shown.

[0078] (Example 3: Shunt resistance) In this experiment, the importance of the thickness of the first Al2O3 layer, which varies from 0 to 2 nm, is verified. Using a Keithley source meter and AM1.5 illumination, light I-V measurements are performed. The shunt resistance is obtained from the reciprocal of the J-V gradient in the short-circuit condition.

[0079] Figure 4 shows the shunt resistance R of the perovskite / Si tandem solar cell as a function of the thickness x of the first Al2O3 layer within the three layers of ALD. shunt The three layers are Al2O3 / SnO2 / 1 nm Al2O3 with a thickness of x nm.

[0080] Experiments were carried out on two different bottom cell wafer types with an inverted perovskite top cell deposited on top. Along with the thickness of Al2O3, all of the device efficiency, fill factor, and shunt resistance increased.

[0081] The plot in Figure 4 shows the optimal cell and the average of 20 devices for each thickness. This experiment was conducted twice, and the results of both batches are shown. A certain positive trend was observed, especially for the devices with optimal characteristics.

Claims

1. A photovoltaic device having a PIN structure, A p-type hole transport layer is supported on the substrate; a perovskite layer and an n-type electron transport layer are disposed in this order on the p-type hole transport layer; a light-transmissive conductive layer is provided on top of the n-type electron transport layer to form a light-receiving upper surface; providing an interface structure between the n-type electron transport layer and the light-transmissive conductive layer, the interface structure having two inorganic electrically insulating layers with a layer of conductive material therebetween; the inorganic electrically insulating layer comprises a material having a bandgap greater than 4.5 eV, and the layer of electrically conductive material comprises a material having a bandgap smaller than the bandgap of the inorganic electrically insulating layer; Each inorganic electrically insulating layer forms a Type 1 offset junction with said layer of electrically conductive material, a photovoltaic device.

2. 10. The photovoltaic device of claim 1, wherein the layer of conductive material comprises a material with a bandgap greater than 2 eV and less than or equal to 4.0 eV.

3. 3. The photovoltaic device of claim 1 or 2, wherein the substrate comprises separate photovoltaic subcells to form a monolithic integrated multi-junction photovoltaic device.

4. The two inorganic electrical insulating layers are Al 2 O 3 4. A photovoltaic device according to claim 1 , comprising:

5. The layer of conductive material between the two inorganic electrically insulating layers is SnO x ZnO x ;(Zn:Sn)O x ; TiO x and InO x 5. A photovoltaic device according to any one of claims 1 to 4, comprising one or more materials selected from the group consisting of:

6. The layer of conductive material between the two inorganic electrically insulating layers is SnO x 6. The photovoltaic device of claim 5, comprising:

7. The other photovoltaic subcells may be made of perovskite, single crystal silicon, polysilicon, Cu(In,Ga)Se 2 , or Cu 2 ZnSn(S,Se) 4 4. The photovoltaic device of claim 3 having a subcell.

8. 8. A photovoltaic device according to any one of claims 1 to 7, wherein the perovskite layer comprises one or more cations selected from one or more of an organic cation and a caesium cation, Pb, Sn, Sb or Ti, and one or more halide anions selected from Cl, Br and I.

9. 9. A photovoltaic device according to any one of the preceding claims, wherein the two inorganic electrically insulating layers have a thickness between 0.4 and 3 nm.

10. 10. A photovoltaic device according to any one of the preceding claims, wherein the layer of electrically conductive material between the two inorganic electrically insulating layers has a thickness between 3 and 12 nm.

11. 1. A photovoltaic device comprising: Cu(In,Ga)Se with p-type and n-type layers 2 or Cu 2 ZnSn(S,Se) 4 and a pn junction of a light-transmissive conductive layer provided on top of the n-type layer forming a light-receiving top surface; having Between the n-type layer and the light-transmissive conductive layer, a structure is provided having two inorganic electrically insulating layers with a layer of conductive material therebetween; The two inorganic electrically insulating layers have a material with a band gap greater than 4.5 eV; A photovoltaic device, wherein said layer of conductive material comprises a material having a bandgap greater than 2 eV and less than 4.0 eV.

12. 12. A method for manufacturing a photovoltaic device according to claim 1, wherein the two inorganic electrically insulating layers and the layer of conductive material in between are deposited, in that order, on the n-type electron transport layer by atomic layer deposition.

13. The method of claim 12 , wherein the atomic layer deposition is performed at a temperature of 125° C. or less.

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