A perovskite photovoltaic element comprising a metal oxide layer between a perovskite photoactive layer and a back electrode, and having a n-i-p-n architecture

Abstract

The present invention relates to a perovskite photovoltaic element (100), comprising a transparent front electrode (2), a back electrode (12), and a stack (20) arranged between the front electrode (2) and the back electrode (12) having a n-i-p-n architecture with a perovskite photoactive layer (5) as i-layer, comprising in sequence the following layers: a) the transparent front electrode (2); b) a doped or non-doped n-type layer (ETL) (3) comprising an electron transport material (ETM), wherein the LUMO of the n-type layer is equal or less negative than -4.4 eV; c) the perovskite photoactive layer (5) comprising at least an inorganic perovskite or an organic perovskite absorber material; d) a doped or non-doped p-type layer (HTL) (7) comprising a hole transport material (HTM), wherein the HOMO of the p-type layer (7) is equal or more negative than -5.0 eV; e) a n-type interlayer (9) comprising an electron transport material (ETM), wherein the LUMO of the n-type interlayer (9) is equal or more negative than -4.0 eV; e) a metal oxide layer (11); and f) the back electrode (12), wherein the back electrode (12) is formed from a metal or an alloy thereof.

Description

[0001]Heliatek GmbH P117WO 27.07.2024 1 / 36 A perovskite photovoltaic element comprising a metal oxide layer between a perovskite photoactive layer and a back electrode, and having a n-i-p-n architecture The present invention relates to a perovskite photovoltaic element, comprising a transparent front electrode, a back electrode, and a stack arranged between the front electrode and the back electrode having a n-i-p-n architecture, comprising a perovskite photoactive layer as i-layer, and a metal oxide layer between the perovskite photoactive layer and the back electrode. Solar cells generate energy by converting light into electricity based on the photovoltaic effect. Different types of solar cells have been developed including CIGS, organic, silicon, and perovskite solar cells. In recent years, perovskite attracted high attention in the field of photovoltaics because of their high theoretical power conversion efficiency (PCE). The power conversion efficiency (PCE) of perovskite solar cells (PSC) increased significantly during the last years. Highly efficient and stable perovskite cells can be developed by optimizing the deposition process, regulating the crystal growth, composition engineering, and optimizing the stack, e.g. by better interface contacts. Metal halide perovskites are a class of optoelectronic materials that have attracted huge attention worldwide. In general, metal halide perovskites can be classified into organic–inorganic hybrid perovskites and inorganic perovskites, where the latter are thermally more stable than the former. Although the power conversion efficiency of inorganic perovskites based solar cells has reached over 20%, inorganic perovskite materials still suffer from instability, in particular towards temperature, light, and / or moisture. For commercialization the instability of perovskite cells needs to be improved resulting in prolonged durability. By adding a thin interlayer of metal oxide, e.g. MoOx or NiOx, between the perovskite photoactive layer and the metal electrode Heliatek GmbH P117WO 27.07.2024 2 / 36 in a nip / metal oxide / metal electrode architecture helps to improve the contact resulting not only in an increased fill-factor and PCE but also an increased stability. Such kind of thin metal oxide layer was reported to also enhance the initial photovoltaic performance of perovskite single junctions. However, the metal oxide layer appeared simultaneously to be one of the sources causing instability of perovskite single junctions. A direct or indirect contact, e.g. a hole transport layer (HTL) in between, in particular an organic hole transport layer, between perovskite photoactive layers and metal oxides shortens the lifetime of perovskite single junctions under thermal and / or light- illumination stressed conditions due to either a chemical reaction of metal oxide and organic cations in hybrid organic-inorganic perovskites or irreversible morphological changes in inorganic perovskites. Light induced into perovskites with interface to a metal oxide layer changes the film morphology under light exposure. This phenomenon was attributed to chemical interaction between metal oxides and perovskite, creating defects that accelerated perovskite crystallization. High work-function molybdenum trioxide (MoO) has been successfully used as hole-injection und -extraction material in organic solar cells. Direct transfer of electrons from the very low-lying conduction band of the n-type MoO into the highest occupied molecular orbital (HOMO) of donor molecules of the adjacent layer is responsible for the efficient hole extraction process. However, the performance of devices comprising a direct contact between MoO and perovskite is degraded due to a chemical reaction at the interface. In case of an air-sensitive electrode material, e.g. Al, the metal oxide layer serves for stabilizing the back electrode material and can prevent from migration of oxygen and moisture into the perovskite photoactive layer. MoOx is generally paired with electrode metals or used as hole contact on top of organic HTLs in n-i-p architecture for efficient hole extraction. Heliatek GmbH P117WO 27.07.2024 3 / 36 It is known from prior art that perovskite solar cells, in particular perovskite photoactive layers, suffer from metal oxide layers resulting in photo- and thermally induced interfacial degradation. In particular, thermal stability of single perovskite cells with a nip / MoOx / metal-structure is surprisingly low. This is attributed to chemical instability at the MoO / perovskite interface. While the strong p-doping ability of MoO is of advantage to facilitate hole extraction from an organic semiconductor layer, this capability to oxidize seems to be detrimental for perovskites. In particular, iodides are considered as the main cause for interface instability, as they are oxidized by MoO. Perez-del-Rey et al. (Chem. Mater. 2019, 31, 6945-6949) discloses molecular passivation of MoO by band alignment and protection of charge transport layers in vacuum-deposited perovskite solar cells. MoO is used to enhance carrier extraction to the transport bottom electrode in a pin-configuration by inserting a molecular interlayer with a lone pair nitrogen and low ionization potential. MoO can also be used on the top of a perovskite absorber in a nip-configuration. In the nip-structure an interfacial modification layer acts as protection layer which prevents MoO diffusion into the underlying layers. Thampy et al. (J. Phys. Chem. Lett. 2021, 12, 8495-8506) discloses metal oxide-induced instability and its mitigation in halide perovskite solar cells. Interfacial degradation of halide perovskites is promoted by contact with metal oxide layers which effects their performance and stability. Interfacial interactions between the perovskite and metal oxides on the stability are critical. Metal oxides can trigger structural instability and irreversible morphological changes in inorganic perovskite absorbers, leading to poor device performance under continuous illumination. Mitigation strategies are discussed to alleviate this metal oxide / perovskite interface-specific degradation to improve their performance and operational stability. Heliatek GmbH P117WO 27.07.2024 4 / 36 Schloemer et al. (ACS Energy Lett. 2020, 5, 2349) discloses that molybdenum oxide interface limits the high-temperature operational stability of perovskite solar cells. An interfacial degradation mechanism concerning the use of MoOx interlayer at the hole- transport layer interface leads to loss of efficiency at high temperature and under illumination. Schulz et al. (ACS Appl. Mater. Interfaces 2016, 8, 31491) discloses high-work-function molybdenum oxide hole extraction contacts in hybrid organic-inorganic perovskite solar cells. The direct contact between MoO and the perovskite leads to a chemical reaction which diminishes device functionality. In order to suppress the chemical reaction at the interface a buffer layer of a hole transport material is arranged between the MoO layer and the perovskite layer. Apergi et al. (9 ACS Appl. Mater. Interfaces 2022, 14, 34208) discloses decomposition of organic perovskite precursors on MoO and the role of halogen and surface defects. Despite the fact that it is often reported that inorganic perovskite solar cells have a higher thermal stability compared to organic counterparts, no inorganic perovskite single junctions so far utilizing an interlayer of metal oxides reach sufficient durability, in particular demanding low degradation under thermal and light stress. The underlying technical problem of the present invention is to overcome the before mentioned problems, in particular, to provide a perovskite subcell of a perovskite photovoltaic element having a metal oxide layer, in particular a MoO layer, having improved stability, in particular increased stability at higher temperature and / or higher durability under illumination of light. The use of metal oxide layers, in particular MoO layers, in perovskite cells suffer from drawbacks. The metal oxide layer lead perovskite cells to be more prone to degradation of the perovskite photoactive layer. Minimization of interfacial reactions between the metal oxide layer and perovskite photoactive layer through interface Heliatek GmbH P117WO 27.07.2024 5 / 36 engineering is crucial for achieving efficient and stable perovskite solar cells. The object is achieved by means of the subject-matter of the independent claims. Advantageous embodiments are evident from the dependent claims. The object of the present invention is in particular solved by a perovskite photovoltaic element, comprising a transparent front electrode, a back electrode, and a stack arranged between the front electrode and the back electrode having a n-i-p-n architecture with a perovskite photoactive layer as i-layer, comprising in sequence the following layers: a) the transparent front electrode; b) a doped or non-doped n-type layer (ETL) comprising an electron transport material (ETM), wherein the LUMO of the n-type layer is equal or less negative than -4.4 eV; c) the perovskite photoactive layer comprising at least an inorganic perovskite or an organic perovskite absorber material; d) a doped or non-doped p-type layer (HTL) comprising a hole transport material (HTM), wherein the HOMO of the p-type layer is equal or more negative than -5.0 eV; e) a n-type interlayer comprising an electron transport material (ETM), wherein the LUMO of the n-type interlayer is equal or more negative than -4.0 eV; e) a metal oxide layer; and f) the back electrode, wherein the back electrode is formed from a metal or an alloy thereof. According to the present invention in particular the metal oxide layer is arranged between the perovskite photoactive layer and the back electrode. In a preferred embodiment the metal oxide layer is directly arranged at the back electrode. According to the present invention in particular an additional n-type interlayer, preferably a n-doped n-type interlayer, is arranged between the metal oxide layer and the p-type layer of a n-i-p architecture of a perovskite cell resulting in a a n-i-p-n cell architecture of the perovskite cell. Heliatek GmbH P117WO 27.07.2024 6 / 36 In the context of the present invention a photoactive layer, in particular a perovskite photoactive layer, is a layer which actively contributes as an absorber layer by absorption of light and converting into electrical energy. In this context the term photoactive is understood to mean the conversion of light energy to electrical energy, e.g. the optoelectronic component converts light energy to electrical energy. Preferably the perovskite photoactive layer is a light-absorbing layer. In the context of the present invention a p-type layer is, in particular, a layer comprising a hole transport material (HTM) or a layer comprising a hole transport material (HTM) and a p-dopant. The p-type layer is in particular a hole transport layer (HTL) and favors the transport of positive charge carriers (holes) of a photoactive layer to an electrode. Preferably the absolute value of the lowest unoccupied molecular orbital (LUMO) of the p-dopant is at least equal to the absolute value of the highest occupied molecular orbital (HOMO) of the corresponding hole transport material (HTM) minus 0.1 eV or larger, preferably minus 0.2 eV or larger, to allow for efficient p-doping. In the context of the present invention an n-type layer is, in particular, a layer comprising an electron transport material (ETM) or a layer comprising an electron transport material (ETM) and an n-dopant. The n-type layer is in particular an electron transport layer (ETL). Preferably the absolute value of the highest occupied molecular orbital (HOMO) of the n-dopant is at least equal to the absolute value of the lowest unoccupied molecular orbital (LUMO) of the corresponding n-type layer plus 0.2 eV or smaller, preferably plus 0.1 eV or smaller, to allow for efficient n-doping. In the context of the present invention an i-layer (intrinsic layer) refers to an undoped layer which might be formed by a single material or a mixture of at least two materials. HOMO- and LUMO-energy levels can be determined from the redox potentials of the molecules, for which measurement methods are Heliatek GmbH P117WO 27.07.2024 7 / 36 sufficiently described in the literature. The measurement by Cyclovoltammetry is described by Lucia Leonat et al. (U.P.B. Sci. Bull., Series B, Vol. 75, Iss. 3, 2013). Alternatively, HOMO and LUMO energies or the corresponding ionization energies and electron affinities can be determined from photoelectron spectroscopy and inverse photoelectron spectroscopy. The perovskite photovoltaic element according to the present invention has advantages in comparison with the prior art. Surprisingly, the lifetime of a perovskite photovoltaic element having a perovskite single junction utilizing an interlayer of metal oxide is increased. Advantageously, a perovskite subcell of a perovskite photovoltaic element comprising a metal oxide layer, in particular a MoO layer, having increased thermal stability is provided. Advantageously, a perovskite subcell of a perovskite photovoltaic element comprising a metal oxide layer, in particular a MoO layer, having higher durability under illumination of light is provided. Advantageously, the degradation of perovskite photovoltaic elements under thermal and / or light stress is reduced. Advantageously, interfacial reactions between the metal oxide layer and perovskite photoactive layer are minimized. Advantageously, an improved stability under illumination and an improved thermal stability of the perovskite single cell compared to a n-i-p- architecture is obtained. Advantageously, the service life of perovskite photovoltaic elements under thermal stress is increased, in particular a decrease in efficiency over time is reduced. Advantageously, the durability of perovskite photovoltaic elements under continuous light illumination is increased, in particular a decrease in efficiency over time is reduced. According to a development of the invention, the work-function of the metal oxide layer is 5.0 eV to 7.0 eV (determined by UPS), preferably 5.5 eV to 7.0 eV, preferably 6.0 eV to 7.0 eV, or preferably 6.5 eV to 7.0 eV, and / or the material of the metal oxide layer is selected from the group consisting of CrOx, InOx, MoOx, NbOx, NiOx, SnOx, TiOx, VOx, WOx, and ZnOx, preferably the metal oxide layer is formed by mixtures of at least thereof. Heliatek GmbH P117WO 27.07.2024 8 / 36 Preferably for CrOx x is 1 to 2.5, for InOx x is 1.5, for MoOx x is 2 to 3, for NbOx, x is 2 to 2.5, for NiOx x is 1 to 1.5, for SnOx x is 1 to 2, for TiOx x is 1 to 2, for Vox x is 1 to 2, for WOx x is 2 to 3, and for ZnOx x is 1. In a preferred embodiment the material of the metal oxide layer is a transition metal oxide. The work-function (also named ionization energy IE (IP); E_HOMO) was determined by UV Photoelectron Spectroscopy (UPS) on thermally vaporized layers (Olthof, Adv. Optical Mater. 2021, 9, 2100227). The layer to be analyzed is deposited in a vacuum on a suitable conductive substrate, e.g. gold, shortly before analysis. For the UPS measurement, a He plasma source providing a high-intensity emission at E(HeIα) =21.22 eV is used. For MoOx the work-function was determined to (Liu et al., Appl. Phys. Lett. 106, 193903 (2015)). Alternatively, other sources like H-Lyman, Ar, Ne, Kr, or Xe plasma sources, VUV lasers (typically around 10 eV), and synchrotron sources can be used. Measurements are typically taken at room temperature. In a preferred embodiment the metal oxide layer is a doped or a non-doped layer. In a preferred embodiment the n-type interlayer is directly arranged at the metal oxide layer. According to a development of the invention, the LUMO of the n- type interlayer is equal or more negative than -4.2 eV, preferably equal or more negative than -4.4 eV, preferably equal or more negative than -4.5 eV, preferably equal or more negative than -4.6 eV, or preferably equal or more negative than -4.7 eV, or the LUMO of the n-type interlayer is in the range of -4.0 eV to -6.0 eV, preferably of -4.2 eV to -5.8 eV, preferably of -4.4 eV to -5.8 eV, or preferably of -4.6 eV to -5.8 eV. This enables a good connection to typically used hole transport layers and ensures a good electrical connection to the metal oxide layer. In a preferred embodiment the electron transport material (ETM) of the n-type interlayer is an organic material. Heliatek GmbH P117WO 27.07.2024 9 / 36 In a preferred embodiment the electron transport material (ETM) of the n-type interlayer is a chemical compound of formula I wherein R to R is H or a substituent selected from the group consisting of halogen, —CN, —NO, —SOR, —SOR, —CF,—COOR), —CONHR, —CONRR′), non-substituted or substituted aryl, non-substituted or substituted heteroaryl, and non-substituted or substituted alkyl, wherein R and R′ are a non-substituted or substituted alkyl or aryl, or wherein R and R, R and R, or R and R together form a ring-structure, wherein the ring-structure is an aromatic ring, a heteroaromatic ring, or an aliphatic ring, which ring-structure can be non-substituted or substituted. According to a development of the invention, the electron transport material (ETM) of the n-type interlayer is selected from the group consisting of Hexaazatriphenylen, preferably comprising six electron-withdrawing groups, Perylenetetracarboxylic dianhydrid (PTCDA) or derivaties thereof, Tetracyanobenzochinondimethan (TCNQ), Tetracyanonaphthochinondimethan (TCNNQ), Radialen or derivaties thereof, preferably the electron transport material (ETM) of the n-type interlayer Dipyrazino[2,3-f:2‘,3‘-h]quinoxaline- 2,3,6,7,10,11-hexacarbonitril (CN-HAT). Heliatek GmbH P117WO 27.07.2024 10 / 36 According to a development of the invention, the n-type interlayer is a n-doped n-type interlayer comprising a n-dopant, preferably the HOMO of the n-dopant of the n-type interlayer is equal or more negative than -4.6 eV, preferably equal or more negative than -4.8 eV, or preferably equal or more negative than -5.0 eV, or the HOMO of the n-dopant of the n-type interlayer is in the range of -4.6 eV to -5.2 eV, preferably of -4.8 eV to -5.2 eV, or preferably of -5.0 eV to -5.2 eV. Preferably the HOMO of the n-dopant of the n- type interlayer is lower compared to the LUMO of electron transport material (ETM) of the n-type interlayer. This enables a charge carrier transfer from the n-dopant to the electron transport material (ETM) of the n-type layer. In the n-type interlayer the use of a weak n-dopant is advantageous, as its low reactivity simplifies production and handling and at the same time enables lifetime, as undesired reactions are prevented. In a preferred embodiment the n-dopant of the n-type interlayer is selected from the group consisting of Pentacen or derivate thereof, TDATA or derivates thereof, preferably m-MTDATA, TAD or derivates thereof, preferably Spiro-MeO-TAD, BPBPA or derivates thereof, TNATA or derivates thereof, preferably 2-TNATA, TPD or derivates thereof, preferably MeO-TPD, and Triarylamin-derivatives having at least one alkyl- or Alkoxy-substituent at least two Aryl-substituents of the Amine. Preferably the n-dopant of the n- doped interlayer is an organic material. Alternative n-dopants of the n-type interlayer are Leuco dyes (e.g. Leuco Crystal Violet), Metallocenes or Metallocene Dimers, Triazinanens, Amines, TTF, TTN, BEDT-TTF, Paddle wheel complexes (e.g. Cr2(hpp)4, W2(hpp)4), 2,3-Dihydro-1H-benzimidazoles and its dimers, 2,3-Dihydro-1H-imidazoles and its dimers, Imidazolium and Benzomidazolium compounds, Perimidines, e.g. 2,3-Dihydro-1H- perimidines and its dimers, Bis-Carbenes, or Viologenes. According to a development of the invention, the ratio of the n- dopant in the n-type interlayer is 0.1 to 30 vol.-%, preferably 1 to 30 vol.-%, preferably 2 to 30 vol.-%, preferably 5 to 30 vol.- %, preferably 0.1 to 20 vol.-%, preferably 1 to 20 vol.-%, Heliatek GmbH P117WO 27.07.2024 11 / 36 preferably 2 to 20 vol.-%, preferably 0.1 to 10 vol.-%, preferably 1 to 10 vol.-%, preferably 2 to 10 vol.-%, preferably 0.1 to 5 vol.-%, or preferably 1 to 5 vol.-%. In a preferred embodiment the glass transition temperature Tg of the n-type interlayer is greater than 120°C. This ensures sufficient layer stability in the application. In a preferred embodiment the n-type interlayer shows low absorption in the wavelength range from 400 nm to 1000 nm which is advantageous to avoid parasitic absorption. Preferably average absorption (1-T-R) of a 30 nm thick layer is < 10%, preferably <5%. According to a development of the invention, the difference between the HOMO of the n-dopant of the n-type interlayer and the LUMO of ETM of the n-type interlayer is in the range of 0.0 eV to 0.6 eV (by amount), preferably of 0.0 eV to 0.4 eV, preferably of 0.2 eV to 0.4 eV, or preferably of 0.0 eV to 0.2 eV, wherein preferably the HOMO of the n-dopant of the n-type interlayer is more negative compared to the LUMO of ETM of the n-type interlayer. According to a development of the invention, the HOMO of the p- type layer is equal or more negative than -5.2 eV, preferably equal or more negative than -5.4 eV, or the HOMO of the p-type layer is in the range of -5.2 eV to -5.8 eV, preferably of -5.2 eV to -5.6 eV. According to a development of the invention, the p-type layer is a doped p-type layer comprising a p-dopant, wherein the LUMO of the p-dopant is equal or more negative than -4.0 eV, preferably more negative than -4.5 eV, preferably equal or more negative than -4.7 eV, preferably equal or more negative than -4.9 eV, or preferably equal or more negative than -5.0 eV, or the LUMO of the p-dopant is in the range of -4.0 eV to -5.6 eV, preferably of -4.2 eV to - 5.6 eV, preferably of -4.2 eV to -5.4 eV, or preferably of -4.5 eV to -5.6 eV. This ensures good bonding of the p-type layer and the Heliatek GmbH P117WO 27.07.2024 12 / 36 metal oxide layer. In a preferred embodiment the hole transport material (HTM) of the p-type layer is an organic material. In a preferred embodiment the hole transport material (HTM) of the p-type layer is selected from the group consisting of N4,N4,N4',N4'-Tetra[(1,1'-biphenyl)-4-yl]-(1,1'-biphenyl)-4,4'- diamine (BPBPA), N4,N4,N4'',N4''-tetra([1,1'-biphenyl]-4-yl)- [1,1':4',1''-terphenyl]-4,4''-diamine (TaTm), N,N'-Bis(naphthalen- 1-yl)-N,N'-bis(phenyl)-benzidine (a-NPD), MeO-TAD, Spiro-MeO-TAD, HTM081, TDATA-Derivate, N4,N4’-Bis (9,9-dimethyl-9H-fluoren-2-yl)- N4,N4’-diphenylbiphenyl-4,4’-diamine (BF-DPB), and N3,N3‘- Di(biphenyl(-4-yl)-N3,N3‘-dimesitylbiphenyl-3,3‘-diamin (HT3). In a preferred embodiment the p-dopant of the p-type layer is an organic dopant. In a preferred embodiment the p-dopant of the p-type layer is selected from the group consisting of 2,2'-(perfluorocyclohexa- 2,5-diene-1,4-diylidene)dimalononitril (TCNQ-1), N'-Dicyan- 2,3,5,6-tetrafluoro-1,4-chinondiimin; N,N'-Dicyan-2,5-dichloro- 1,4-chinondiimin, N,N'-Dicyan-2,5-dichloro-3,6-difluoro-1,4- chinondiimin, N,N'-Dicyan-2,3,5,6,7,8-hexafluoro-1,4- naphthochinondiimin, 1,4,5,8-Tetrahydro-1,4,5,8-tetrathia-2,3,6,7- tetracyano-anthrachinon, 1,3,4,5,7,8-Hexafluoronaphtho-2,6- chinontetracyanomethan (TCNQ-7), 2,2'-(2,5-Dibrom-3,6- difluorcyclobexa-2,5-dien-1,4-diyliden)dimalononitril, 4,4'- (1E,1'E)-(2-cyano-3,6-difluoro-5-isocyanocyclohexa-2,5-diene-1,4- diylidene)bis-(cyanomethan-1-yl-1-ylidene)bis(2,3,5,6- tetrafluorobenzonitril), 2,2',2"- (Cyclopropan-1,2,3 - triyliden)tris(2-(2,6-dichlor-3,5-difluor-4- (trifluormethyl)phenyl)acetonitril), (2E,2'E,2"E)-2,2',2"- (cyclopropane-1,2,3-triylidene)tris(2- (perfluorophenyl)acetonitril), 2,2',2"-(cyclopropane-1,2,3- triylidene)tris(2-(perfluorobiphenyl-4-yl)acetonitril), 2,2',2"- (cyclopropane-1,2,3-triylidene)tris(2-(2,6-dichloro-3,5-difluoro- 4-(trifluoromethyl)phenyl)-acetonitril), and Benzene-acetonitril, α,α',α"-1,2,3-cyclopropanetriylidenetris[4-cyano-2,3,5,6- tetrafluoro-(PR-1), 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyano- Heliatek GmbH P117WO 27.07.2024 13 / 36 quinodimethane (F4TCNQ), 2,2'-(1,3,4,5,7,8-Hexafluoro-2,6- naphthalenediylidene)bis-propanedinitrile (F6TCNNQ), and NDP9. In a preferred embodiment the p-dopant of the p-type layer is selected from the group consisting of NDP2, NDP9, C60-F36, and C60-F48. NDP2 and NDP9 are commercial p-dopants of Novaled GmbH. In a preferred embodiment the layer thickness of the p-type layer is 10 nm to 50 nm, preferably 10 nm to 30 nm. According to a development of the invention, the difference between the HOMO of the p-type layer and the LUMO of the n-type interlayer is 2.0 eV at maximum, preferably 1.5 eV at maximum, or preferably 1.0 eV at maximum, and / or the difference between the HOMO of the p-type layer and the LUMO of the n-type interlayer is in the range of 0.3 eV to 1.2 eV (by amount), preferably of 0.5 eV to 1.0 eV, or preferably of 0.5 eV to 0.8 eV. According to a development of the invention, the difference between the HOMO of the p-type layer and the LUMO of the n-type interlayer is smaller than the difference between the HOMO of the n-type interlayer and the HOMO of the p-type layer, preferably at minimum 0.3 eV (by amount), or preferably at minimum 0.6 eV. According to a development of the invention, the metal oxide layer has a layer thickness of 5 nm to 50 nm, preferably 10 nm to 30 nm, and / or the n-type interlayer has a layer thickness of 10 nm to 100 nm, preferably 10 nm to 50 nm, preferably 10 nm to 30 nm, preferably 15 nm to 30 nm, or preferably 15 nm to 25 nm. In a preferred embodiment the n-type layer is an intrinsic n-type layer. In an alternative preferred embodiment the n-type layer is a doped n-type layer comprising a n-dopant, preferably an organic n-dopant. In the context of the present invention a non-doped n-type layer is an intrinsic n-type layer and a non-doped p-type layer is an intrinsic p-type layer. Heliatek GmbH P117WO 27.07.2024 14 / 36 According to a development of the invention, a non-doped n-type layer comprising at least one electron transport material (ETM) is arranged between the n-type layer and the perovskite photoactive layer, and / or a non-doped p-type layer comprising at least one hole transport material (HTM) is arranged between the p-type layer and the perovskite photoactive layer, wherein preferably the non- doped n-type layer and / or the non-doped p-type layer are directly arranged at the perovskite photoactive layer. According to a development of the invention, the perovskite absorber material of the perovskite photoactive layer is an inorganic perovskite, preferably a three-dimensional halide perovskite, a double perovskite, or a combination thereof, wherein preferably the three-dimensional halide perovskite having a formula ABX, wherein A is selected from Cs, Na, K, Rb, or a combination thereof; B is selected from Pb, Sn, Ge, Cu, Fe, Ga, Eu, Sr, Ti, Mn, Bi, Zn, Mg, Ca, Ba, Y, Yb, Co, In, Sb, Bi, Ag, Ni, Ho, Er, Tb, Sm, La, or a combination thereof; and X is selected from F, Cl, Br, I, or a combination thereof; and wherein preferably the double perovskite having a formula ABCX, wherein A is selected from Cs, Rb, or combination thereof; B is selected from Cu, Ag, Hg, Au, or a combination thereof; C is selected from Sb, Bi, In or a combination thereof; and X is selected from F, Cl, Br, I, or a combination thereof. In a preferred embodiment the perovskite absorber material of the perovskite photoactive layer is an all-inorganic perovskite, preferably the all-inorganic perovskite is selected from the group consisting of CsPbI, CsPbBrI, CsPbBrI, CsPbBr, CsPbClI, CsPbClI, CsPbCl, CsPbBrCl, CsPbBrCl, CsPbBrClI, and mixtures thereof. In a preferred embodiment the perovskite photoactive layer has a layer thickness of 50 nm to 500 nm, preferably 50 nm to 400 nm, preferably 50 nm to 300 nm, preferably 100 to 500 nm, preferably 100 nm to 400 nm, preferably 100 to 300 nm, preferably 100 nm to 200 nm, preferably 100 nm to 200 nm, preferably 150 nm to 300 nm, or preferably 200 nm to 500 nm. Heliatek GmbH P117WO 27.07.2024 15 / 36 According to a development of the invention, the material of the back electrode is selected from the group consisting of Al, Au, Ag, Co, Cr, Cu, and Ni, or an alloy thereof. In a preferred embodiment the material of the transparent front electrode is indium tin oxide (ITO), fluorine doped tin oxide (FTO), indium zinc oxide, InZnAlO, ZnAlO, a conductive nanotube, a conductive nanoparticle, cadmium oxide, zirconium indium oxide, gallium zinc oxide, graphene, graphene oxide, graphite, carbon nanotube, carbon, Ag, Al, Au, Mo, Cu, Ni, Ca, Li, or a conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) or a combination thereof. In a preferred embodiment the transparent front electrode is arranged at a light-facing side of the optoelectronic component as intended. In a preferred embodiment the LUMO of the n-type layer is equal or less negative than -4.2 eV, or preferably equal or less negative than -4.0 eV, or the LUMO of the n-type layer is in the range of - 4.4 eV to -3.0 eV, preferably in the range of -4.2 eV to -3.0 eV, or preferably in the range of -4.0 eV to -3,2 eV. In a preferred embodiment the electron transport material (ETM) of the n-type layer is a fullerene or a fullerene derivative, preferably selected from the group consisting of C60, C70, C76, C80, C82, C84, C86, C90 und C94, or a derivative thereof, wherein the derivative preferably is a halogenated fullerene, a hydroxylated fullerene, a carboxylated fullerene, or an aminated fullerene, preferably the fullerene is C60, C70 and / or a derivative thereof, more preferably fullerene C60. In a preferred embodiment the n-type layer comprises an electron transport material (ETM), preferably the electron transport material (ETM) is selected from the group consisting of a fullerene or a fullerene derivative, NTCDA, and NTCDI or a derivative thereof. Preferably the fullerene or a fullerene derivative is selected from the group consisting of C60, C70, C76, Heliatek GmbH P117WO 27.07.2024 16 / 36 C80, C82, C84, C86, C90 und C94, or a derivative thereof, more preferably fullerene C60. In a preferred embodiment the n-type layer is a non-doped n-type layer, preferably consisting of an electron transport material (ETM). In a preferred embodiment the p-type layer is a non-doped p-type layer, preferably hole transport material (HTM), and / or a doped p- type layer, preferably a hole transport material (HTM) and a p- dopant. In a preferred embodiment the n-type layer is a non-doped n-type layer, preferably electron transport material (ETM), and / or a doped n-type layer, preferably electron transport material (ETM) and an n-dopant. Preferably the absolute value of the HOMO of the n-dopant should be at least equal to the absolute value of the LUMO of the corresponding n-type layer plus 0.2 eV or smaller to allow for efficient n-doping. Preferably the absolute value of the LUMO of the p-dopant should be at least equal to the absolute value of the HOMO of the corresponding p-type layer minus 0.2 eV or larger to allow for efficient p-doping. In a preferred embodiment a non-doped p-type layer comprising a hole transport material (HTM) is arranged between the perovskite photoactive layer and the doped p-type layer, wherein preferably the hole transport material (HTM) of the non-doped p-type layer is an organic material. In a preferred embodiment the doped or non-doped p-type layer (HTL) is formed by a first doped or non-doped p-type layer, preferably a first doped p-type layer, and a second doped or non- doped p-type layer, preferably a second doped p-type layer, wherein the first doped or non-doped p-type layer is arranged facing the perovskite photoactive layer and the second doped or non-doped p-type layer is arranged facing the metal oxide layer. Preferably the p-dopant of the first doped p-type layer is an organic p-dopant, and / or the p-dopant of the second doped p-type layer is an organic p-dopant. Heliatek GmbH P117WO 27.07.2024 17 / 36 In a preferred embodiment between the n-type interlayer and the metal oxide layer and / or between the n-type interlayer and the p- type layer, preferably the doped p-type layer, an additional intrinsic n-type layer is arranged. In a preferred embodiment the n-dopant of the n-type layer has a HOMO equal or more positive than -5,0 eV, preferably equal or more positive than -4,8 eV. In a preferred embodiment the n-dopant of the n-type layer is an organic n-dopant, preferably selected from the group consisting of 2,2'-Diisopropyl-1,1',3,3'-tetramethyl- 2,2',3,3',4,4',5,5',6,6',7,7'-dodecahydro-2,2'- bibenzo[d]imidazol (NDR-1); 4,4',5,5'-Tetracyclohexyl-1,1',2,2',3,3'-hexamethyl- 2,2',3,3'-tetrahydro-2,2'-biimidazol (NDR-2); 2,2'-diisopropyl- 4,4',5,5'-tetrakis(2-methoxyphenyl)-1,1',3,3'-tetramethyl- 2,2',3,3'-tetrahydro-1H,1'H-2,2'-biimidazol (NDR-3); 2,2'- diisopropyl-1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-1H,1'H- 2,2'-bibenzo[d]imidazol (NDR-4); 2,2'-diisopropyl-4,4',5,5'- tetrakis(3-methoxyphenyl)-1,1',3,3'-tetramethyl-2,2',3,3'- tetrahydro-1H,1'H-2,2'-biimidazol (NDR-5); 2-Isopropyl-1,3- dimethyl-2,3,6,7-tetrahydro-5,8-dioxa-1,3-diaza- cyclopenta[b]naphthene; Bis-[1,3-dimethyl-2-isopropyl-1,2-dihydro- benzimidazolyl-(2)]; 2,2'-Diisopropyl-4,5-bis (2-methoxyphenyl)- 4',5'-bis(4-methoxyphenyl)-1,1',3,3'-tetramethyl-2,2',3,3'- tetrahydro-2,2'-biimidazol, and NDN45. In a preferred embodiment, the front electrode, the back electrode, and the stack of the perovskite photovoltaic element are arranged on a substrate, preferably the substrate is formed by a polymer layer, preferably the polymer layer is selected from the group consisting of ethylene tetrafluoroethylene (ETFE), polyethylene terephthalate (PET), polyolefin, polyetheretherketone (PEEK), polymethyl methacrylate (PMMA), polypropylene (PP), polyethylene (PE), polyethylene naphthalate (PEN), ethylene vinyl acetate (EVA), polyacrylate (PA), polycarbonate (PC), and thermoplastic polyurethane (TPU). Heliatek GmbH P117WO 27.07.2024 18 / 36 In a preferred embodiment the materials of the stack are processable by vacuum deposition. In a preferred embodiment the layers of the stack are applied by vacuum deposition. Description of the Drawings The invention is described in more detail with reference to working examples and figures: Fig. 1 a schematic illustration of an exemplary embodiment of a stack of a perovskite photovoltaic element in cross-section; Fig. 2 a schematic illustration of an exemplary embodiment of a stack of a perovskite photovoltaic element in cross-section; Fig. 3 a schematic illustration of an exemplary embodiment of a stack of a perovskite photovoltaic element in cross-section; Fig. 4 a schematic illustration of an exemplary embodiment of a stack of a perovskite photovoltaic element in cross-section; Fig. 5 in an exemplary embodiment the thermal stability of a non- inventive n-i-p perovskite photovoltaic element and an inventive n-i-p-n perovskite photovoltaic element; Fig. 6 in an exemplary embodiment the durability under continuous light illumination of a non-inventive n-i-p perovskite photovoltaic element and an inventive n-i-p-n perovskite photovoltaic element; and Fig. 7 in exemplary embodiments inventive and non-inventive perovskite photovoltaic element 100 with a variation of layer thickness of the n-type interlayer 9. The examples are intended to describe the invention without restricting it. It can be demonstrated that the stability of a perovskite cell comprising a metal oxide layer 11 between the perovskite photoactive layer 5 and the back electrode 12 can be improved. Identical and functionally identical elements are provided with the same reference signs, so that in this respect reference is made to the preceding description. The layer thicknesses and the ratio of the layer thicknesses to each other do not correspond to the actual dimensions. Heliatek GmbH P117WO 27.07.2024 19 / 36 In particular, it is shown that a component with a nipn structure has an improved service life compared to a corresponding element with a nip structure. This shows an increased service life under thermal load. Fig. 1 shows a schematic illustration of an exemplary embodiment of a stack 20 of a perovskite photovoltaic element 100 in cross- section. The perovskite photovoltaic element 100, comprises a transparent front electrode 2, a back electrode 12, and the stack 20 arranged between the front electrode 2 and the back electrode 12 having a n-i-p-n architecture with a perovskite photoactive layer 5 as i- layer. The stack 20 comprises in sequence the following layers: a) the transparent front electrode 2; b) a doped or non-doped n- type layer (ETL) 3 comprising an electron transport material (ETM), wherein the LUMO of the n-type layer 3 is equal or less negative than -4.4 eV; c) the perovskite photoactive layer 5 comprising at least an inorganic perovskite or an organic perovskite absorber material; d) a doped or non-doped p-type layer (HTL) 7 comprising a hole transport material (HTM), wherein the HOMO of the p-type layer 7 is equal or more negative than -5.0 eV; e) a n-type interlayer comprising 9 an electron transport material (ETM), wherein the LUMO of the n-type interlayer 9 is equal or more negative than -4.0 eV; e) a metal oxide layer 11; and f) the back electrode 12, wherein the back electrode 12 is formed from a metal or an alloy thereof. In a further embodiment of the invention the work-function of the metal oxide layer 11 is 5.0 eV to 7.0 eV (determined by UPS), preferably 5.5 eV to 7.0 eV, preferably 6.0 eV to 7.0 eV, or preferably 6.5 eV to 7.0 eV, and / or the material of the metal oxide layer 11 is selected from the group consisting of CrOx, InOx, MoOx, NbOx, NiOx, SnOx, TiOx, VOx, WOx, and ZnOx. In a further embodiment of the invention the LUMO of the n-type interlayer 9 is equal or more negative than -4.2 eV, preferably equal or more negative than -4.4 eV, preferably equal or more Heliatek GmbH P117WO 27.07.2024 20 / 36 negative than -4.5 eV, preferably equal or more negative than -4.6 eV, or preferably equal or more negative than -4.7 eV, or the LUMO of the n-type interlayer (9) is in the range of -4.0 eV to -6.0 eV, preferably of -4.2 eV to -5.8 eV, preferably of -4.4 eV to - 5.8 eV, or preferably of -4.6 eV to -5.8 eV. In a further embodiment of the invention the n-type interlayer 9 is a n-doped n-type interlayer 9 comprising a n-dopant, preferably the HOMO of the n-dopant of the n-type interlayer 9 is equal or more negative than -4.6 eV, preferably equal or more negative than -4.8 eV, or the HOMO of the n-dopant of the n-type interlayer 9 is in the range of -4.6 eV to -5.2 eV, preferably of -4.8 eV to -5.2 eV, or preferably of -5.0 eV to -5.2 eV. In a further embodiment of the invention the ratio of the n-dopant in the n-type interlayer 9 is 0.1 to 30 vol.-%, preferably 1 to 30 vol.-%, preferably 0.1 to 20 vol.-%, preferably 1 to 20 vol.-%, preferably 0.1 to 10 vol.-%, preferably 1 to 10 vol.-%, preferably 0.1 to 5 vol.-%, or preferably 1 to 5 vol.-%. In a further embodiment of the invention the difference between the HOMO of the n-dopant of the n-type interlayer 9 and the LUMO of the ETM of the n-type interlayer 9 is in the range of 0.0 eV to 0.6 eV (by amount), preferably of 0.0 eV to 0.4 eV, preferably of 0.2 eV to 0.4 eV, or preferably of 0.0 eV to 0.2 eV, wherein preferably the HOMO of the n-dopant of the n-type interlayer 9 is more negative compared to the LUMO of the ETM of the n-type interlayer 9. In a further embodiment of the invention the HOMO of the p-type layer 7 is equal or more negative than -5.2 eV, preferably equal or more negative than -5.4 eV, or the HOMO of the p-type layer 7 is in the range of -5.2 eV to -5.8 eV, preferably of -5.2 eV to - 5.6 eV. In a further embodiment of the invention the p-type layer 7 is a doped p-type layer 7 comprising a p-dopant, preferably an organic p-dopant, wherein the LUMO of the p-dopant is equal or more negative than -4.0 eV, preferably more negative than -4.5 eV, Heliatek GmbH P117WO 27.07.2024 21 / 36 preferably equal or more negative than -4.7 eV, or preferably equal or more negative than -5.0 eV, or the LUMO of the p-dopant is in the range of -4.0 eV to -5.6 eV, preferably of -4.2 eV to - 5.6 eV, preferably of -4.2 eV to -5.4 eV, or preferably of -4.5 eV to -5.6 eV. In a further embodiment of the invention the difference between the HOMO of the p-type layer 7 and the LUMO of the n-type interlayer 9 is 2.0 eV at maximum, preferably 1.5 eV at maximum, or preferably 1.0 eV at maximum, and / or the difference between the HOMO of the p-type layer 7 and the LUMO of the n-type interlayer 9 is in the range of 0.3 eV to 1.2 eV (by amount), preferably of 0.5 eV to 1.0 eV, or preferably of 0.5 eV to 0.8 eV. In a further embodiment the difference between the HOMO of the p- type layer 7 and the LUMO of the n-type interlayer 9 is smaller than the difference between the HOMO of the n-type interlayer 9 and the HOMO of the p-type layer 7, preferably at minimum 0.3 eV (by amount), or preferably at minimum 0.6 eV. In a further embodiment the metal oxide layer 11 has a layer thickness of 5 nm to 50 nm, preferably 10 nm to 30 nm, and / or the n-type interlayer 9 has a layer thickness of 10 nm to 100 nm, preferably 10 nm to 50 nm, preferably 10 nm to 30 nm, preferably 15 nm to 30 nm, or preferably 15 nm to 25 nm. Perovskite solar cells can be manufactured by solution-processing techniques or by vacuum deposition. The manufacturing of perovskite solar cells by vacuum deposition of individual layers on a substrate is a widely adopted technology in the coating and semiconductor industry and of advantage for large scale production. Vacuum deposition allows strict control over composition and thickness of layers of the perovskite solar cell. Vacuum deposition of perovskite solar cells usually involves the co-sublimation of at least two kinds of precursors in a vacuum chamber which together from the perovskite structure. The substrate can be a flexible substrate, e.g. a film from PET. The layers can be deposited in a roll-to-roll process. Heliatek GmbH P117WO 27.07.2024 22 / 36 In an exemplary embodiment the perovskite cell of the perovskite photovoltaic element 100 is manufactured as follows: The perovskite cell is manufactured by thermal evaporation processes in chambers kept under high vacuum, typically below 10 mbar, at substrate 1 temperature of 30°C. Vacuum deposition of the individual layers of the stack 20, the metal oxide layer 11, and the back electrode 12 was used to manufacture the perovskite photovoltaic element 100. The layers are formed step by step one after the other. A substrate 1 made from a PET film coated with ITO as front electrode 2 was loaded into a vacuum chamber. A n- doped n-type layer 3 was deposited by co-evaporating fullerene C60 and NDN45 (10 nm) at a deposition rate of 0.2 to 0.3 Å / s on the ITO (100 nm) coated PET film followed by fullerene C60 (15 nm) at a deposition rate of 0.2 to 0.3 Å / s to create an n-type layer 4 as electron transport layer (ETL). An all-inorganic CsPbIBr perovskite photoactive layer 5 was subsequently formed on the n- type layer 4 by co-evaporating two precursors simultaneously, a first precursor CsBr and a second precursor PbI, at deposition rates of 0.2 Å / s and 0.31 Å / s, respectively. The thickness of the perovskite photoactive layer 5 was in a range of 100 to 400 nm. A layer of a hole transport material (HTM) N4,N4'-Bis(9,9-dimethyl- 9H-fluoren-2-yl)-N4,N4'-diphenylbiphenyl-4,4'-diamine (BF-DPB) or N,N,N',N'-Tetra([1,1'-biphenyl]-4-yl)[1,1':4',1''-terphenyl]- 4,4''-diamine (TaTm) (10 nm) was applied at a deposition rate of 0.3 Å / s on top of the perovskite photoactive layer 5 to form an intrinsic p-type layer 6 as hole transport layer (HTL), and by co- evaporating TaTm as hole transport material (HTM) and NDP9 as p- dopant in a ratio of 10 vol.-% (30 nm) at a deposition rate of 1.0 Å / s a p-doped p-type layer 7 was formed. Subsequently the n-type interlayer 9 was applied by co-evaporating CN-HAT as hole transport material and 20 wt.-% of the n-dopant TNATA at a deposition rate of 0.5 Å / s. After applying MoOx as metal oxide layer 11, an Au metal was deposited at a rate of 1.0 Å / s to a thickness of 50 nm to form the back electrode 12, e.g. by Al, Ag, Au or a combination thereof. Heliatek GmbH P117WO 27.07.2024 23 / 36 In this example, complete stack 20 including back electrode 12 was applied by vacuum deposition and processed in a roll-to-roll process. Deposition of the layers at higher deposition rate or lower deposition rate is possible, preferably in the range of 0.1 to 10 Å / s. In an alternative embodiment an additional layer of a p-dopant forming a second p-doped p-type layer 8 was applied between the doped p-type layer 7 and the n-type interlayer 9 to optimize the electrical contact to the metal oxide layer 11. Fig. 2 shows a schematic illustration of an exemplary embodiment of a stack 20 of a perovskite photovoltaic element 100 in cross- section. The stack 20 corresponds to that in Fig. 1 but having an n-type interlayer 9 between the p-type layer 7 and the metal oxide layer 11. In this embodiment the n-type layer 3 is a n-doped n- type layer 3, wherein an intrinsic (non-doped) n-type layer 4 is arranged between the n-doped n-type layer 3 and the perovskite photoactive layer 5, and the p-type layer 7 is a p-doped p-type layer 7, wherein an intrinsic (non-doped) p-type layer 6 is arranged between the doped p-type layer 7 and the perovskite photoactive layer 5. In a further embodiment a non-doped n-type layer 4 comprising at least one electron transport material (ETM) is arranged between the n-type layer 3 and the perovskite photoactive layer 5, and a non-doped p-type layer 6 comprising at least one hole transport material (HTM) is arranged between the p-type layer 7 and the perovskite photoactive layer 5, wherein the non-doped n-type 4 layer and the non-doped p-type layer 6 are directly arranged at the perovskite photoactive layer 5. Fig. 3 shows a schematic illustration of an exemplary embodiment of a stack 20 of a perovskite photovoltaic element 100 in cross- section. The stack 20 corresponds to that in Fig. 2 but having an n-type interlayer 9 between the p-type layer 7 and the metal oxide layer 11. In this embodiment the n-type interlayer 9 is a n-doped n-type interlayer 9, wherein additionally an intrinsic n-type Heliatek GmbH P117WO 27.07.2024 24 / 36 interlayer 10 is arranged between the doped n-type interlayer 9 and the metal oxide layer 11. Fig. 4 shows a schematic illustration of an exemplary embodiment of a stack of a perovskite photovoltaic element 100 in cross- section. The stack 20 corresponds to that in Fig. 2 but having an n-type interlayer 9 between the p-type layer 7 and the metal oxide layer 11. In this embodiment a second doped p-type layer 8 is arranged between the doped p-type layer as first doped p-type layer 7 and the n-type interlayer 10. Working examples Within the frame-work of this invention variations in the layer structure of perovskite single junction cells prepared in a R&D vacuum deposition tool (Kurt J. Lesker Company) were examined under different aging conditions. A non-inventive perovskite cell (layer sequence A) having a n-i-p cell architecture as comparative example was compared to inventive perovskite cells (layer sequence B, C, D) having a n-i-p-n cell architecture. The stack 20 of the perovskite photovoltaic element 100 is summarized in table 1. The layer sequence of the reference and the examples are: layer sequence A: ITO / n-C60(5nm) / C60(15nm) / PbI2:CsBr (1:1 mol;100nm) / BF-DPB(10nm) / p- BF-DPB(10nm) / p-TaTm(20nm) / MoOx(25nm) / Al(100nm) layer sequence B: ITO / n-C60(5nm) / C60(15nm) / PbI2:CsBr (1:1 mol;100nm) / BF-DPB(10nm) / p-BF- DPB(10nm) / p-TaTm(10nm) / n-CNHAT(10nm) / MoOx(25nm) / Al(100nm) layer sequence C: ITO / n-C60(5nm) / C60(15nm) / PbI2:CsBr (1:1 mol;100nm) / BF-DPB(10nm) / p- BF-DPB(10nm) / p-TaTm(10nm) / n-CNHAT(20nm) / MoOx(15nm) / Al(100nm) layer sequence D: ITO / n-C60(5nm) / C60(15nm) / PbI2:CsBr (1:1 mol;100nm) / BF-DPB(10nm) / p- BF-DPB(10nm) / p-TaTm(10nm) / n-CNHAT(30nm) / MoOx(5nm) / Al(100nm) The experiments were carried out particularly on glass substrates coated with pre-structured tin-doped indium oxide ITO. The Heliatek GmbH P117WO 27.07.2024 25 / 36 substrates are cleaned with organic solvents, followed by treatment in oxygen plasma. Vacuum deposition of the individual layers of the stack 20, the metal oxide layer 11 as well as the back electrode 12 was used to manufacture the perovskite photovoltaic element. The layers of the perovskite cell are applied by thermal evaporation in chambers kept under high vacuum, typically at below 10 mbar. The perovskite photovoltaic element 100 comprises a substrate 1, e.g. a glass, with transparent ITO (indium-tin-oxide) as front electrode 2. A n-doped n-type layer 3 was formed by co-evaporating fullerene C60 and NDN45 (5 nm) at a deposition rate of 0.3 Å / s, followed by fullerene C60 (15 nm) to form an intrinsic n-type layer 4 as electron transport layer (ETL). An inorganic CsPbIBr perovskite photoactive layer 5 was subsequently formed on the intrinsic n-type layer 4 by co-evaporating the perovskite precursors PbI2 and CsBr in a molar ration at a deposition rate of 0.5 Å / s, respectively, for a thickness of 100 nm. To facilitate the hole transport towards the back electrode 12 an intrinsic p- type layer 6 (HTL) of a hole transport material (HTM) N4,N4’-Bis (9,9-dimethyl-9H-fluoren-2-yl)-N4,N4’-diphenylbiphenyl-4,4’- diamine (BF-DPB) (10 nm) followed by a p-doped p-type layer 7 by co-evaporating BF-DPB as hole transport material (HTM) and NDP9 as p-dopant in a ratio of 10 vol.-% and a second p-doped p-type layer 8 by co-evaporating N4,N4,N4'',N4''-tetra([1,1'-biphenyl]-4-yl)- [1,1':4',1''-terphenyl]-4,4''-diamine (TaTm) and NDP9 as p-dopant in a ratio of 10 vol.-% at deposition rate of 0.3 Å / s were applied on the top of the perovskite photoactive layer 5. By co- evaporating CN-HAT as ETM and m-MTDATA as n-dopant in a ratio of 20 vol.-% at a deposition rate of 1.0 Å / s a n-type interlayer 9 was applied. Depending on the design of the perovskite cell, a protective metal oxide layer 11 by thermal deposition of MoO at a deposition rate of 0.3 Å / s and thickness variation of 3 nm to 25 nm was applied to n-type interlayer 9. Finally, a layer of Al (100 nm) was deposited at a deposition rate of 1.0 Å / s as back electrode 12. The completed perovskite cells are encapsulated in a Heliatek GmbH P117WO 27.07.2024 26 / 36 nitrogen-filled glovebox using glass encapsulation, sealed with a UV-hardened epoxy adhesive. The corresponding structure of the perovskite cells is shown in table 1: Table 1 layer material thickness / nm back electrode 12 Al 100 metal oxide layer 11 MoO 25 / 25 / 15 / 5 n-type interlayer 9 CNHAT:m-MTDATA 0 / 10 / 20 / 30 (2 vol.-%) second p-doped p-type layer 8 TaTm:NDP9 20 / 10 / 10 / 10 (10 vol.-%) first p-doped p-type layer 7 BF-DPB:NDP9 10 (10 vol.-%) intrinsic p-type layer 6 BF-DPB 10 perovskite photoactive layer 5 PbI2:CsBr 100 (1:1 molar ratio) intrinsic n-type layer 4 C60 15 n-doped n-type layer 3 C60:NDN45 5 (20 vol.-%) front electrode 2 ITO 100 ITO: indium tin oxide NDP9: commercial p-dopant of Novaled GmbH TaTm: N4,N4,N4'',N4''-tetra([1,1'-biphenyl]-4-yl)-[1,1':4',1''-terphenyl]-4,4''-diamine NDN45: commercial n-dopant of Novaled GmbH BF-DPB: N4,N4’-Bis (9,9-dimethyl-9H-fluoren-2-yl)-N4,N4’-diphenylbiphenyl-4,4’-diamine m-MTDATA: 4,4',4''-Tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine HOMO / LUMO energy levels of materials of the working examples are summarized in Table 2. Table 2 Heliatek GmbH P117WO 27.07.2024 27 / 36 material LUMO [eV] HOMO [eV] BF-DPB -2.3 -5.4 TaTm-2.35 -5.4 CNHAT -5.1 -7.5 m-MTDATA -2.0 -5.1 NDP9-5.4C60 -4.0 -5.6 TNATA-2.2-5.0 NDN45-2.6-4.5 The perovskite cells are then aged under different stress conditions, either at 85°C in a drying oven or under continuous illumination at AM1.51000 W / m² and 60°C with open contacts and characterized in regular intervals. Each variation in the layer sequence and each type of aging was carried out with 12 individual perovskite photovoltaic elements 100. The current-voltage curves of the perovskite photovoltaic elements 100 were measured using a Keithley 2400 source measure unit under AM1.5 sun simulator (AM = air mass; AM=1.5, radiant power 1000 W / m), directly after preparation and at different times during the aging process. The current-voltage curves of the perovskite photovoltaic elements were measured. The parameters open-circuit voltage Voc, short- circuit current Jsc, fill-factor FF, and the resulting cell performance (power conversion efficiency - PCE) of the perovskite photovoltaic element 100 for the non-inventive perovskite cell (layer structure A) and for the invention perovskite cell (layer structure C) is summarized in table 3. Table 3 Heliatek GmbH P117WO 27.07.2024 28 / 36 Table 3 shows under different aging conditions a direct comparison of a non-inventive perovskite cell (layer structure A) for dry heat (85°C) nip02 and continuous illumination nip52, and an inventive perovskite cell (layer structure C) for dry heat (85°C) nipn04 and continuous illumination nipn54. The relative PCE after 1702 hours dry heat (85°C) for the inventive perovskite cell is 90% (nip04) while it is for the non- inventive perovskite cell 6% (nip02) only, and after continuous illumination for the inventive perovskite cell is 90% (nip54) while it is for the non-inventive perovskite cell 57% (nip52) only (each compared to its initial value). Advantageously by using an additional n-type interlayer 9 between the metal oxide layer 11 and the n-i-p architecture of perovskite cells forming a n-i-p-n architecture according to the present invention, thermal stability in dry heat aging at 85°C is significantly improved (see Fig. 5) without sacrificing the durability under continuous light illumination (see Fig. 6). Thus, it is demonstrated that the specific n-i-p-n architecture of a perovskite cell of the present invention is superior compared to the corresponding n-i-p structure. Heliatek GmbH P117WO 27.07.2024 29 / 36 Fig. 5 shows in an exemplary embodiment the thermal stability of a non-inventive n-i-p perovskite photovoltaic element and an inventive n-i-p-n perovskite photovoltaic element 100. In this exemplary embodiment non-inventive perovskite cells of layer sequence A having a n-i-p cell architecture are compared to inventive perovskite cells of layer sequence C having a n-i-p-n cell architecture (see working example). The thermal stability in dry heat aging at 85°C for 1702 hours is significantly improved (see Fig. 5). While the relative PCE of the inventive perovskite cells of layer sequence C having a n-i-p-n cell architecture is still about 90% of the initial value, for the comparative non-inventive perovskite cells of layer sequence A having a n-i-p cell architecture a relative PCE of 6% of the initial value can only be determined. Fig. 6 shows in an exemplary embodiment the durability under continuous light illumination of a non-inventive n-i-p perovskite photovoltaic element and an inventive n-i-p-n perovskite photovoltaic element 100. In this exemplary embodiment non-inventive perovskite cells of layer sequence A having a n-i-p cell architecture are compared to inventive perovskite cells of layer sequence C having a n-i-p-n cell architecture (see working example). The durability under continuous light illumination at 60°C for 1702 hours is significantly improved (see Fig. 6). While the relative PCE of the inventive perovskite cells of layer sequence C having a n-i-p-n cell architecture is still about 90% of the initial value, for the comparative non-inventive perovskite cells of layer sequence A having a n-i-p cell architecture a relative PCE of 57% of the initial value can only be determined. The results of the non-inventive n-i-p perovskite cell show strong degradation of nip-cells, indicating the formation of an injection and extraction barrier due to p-type (HTL) / MoO interface, and loss of active area over time (Jsc degradation). Heliatek GmbH P117WO 27.07.2024 30 / 36 In the well-known n-i-p architecture of perovskite cells with an aluminum back electrode and a thin electrode stabilizing layer of MoOx leads to low thermal and light induced durability of perovskite single junctions which is overcome by an n-type interlayer 9 of the n-i-p-n architecture of perovskite cells of the present invention. The experimental data demonstrate that the durability of perovskite photovoltaic elements 100 having a metal oxide layer 11 at the back electrode 12 is significantly improved by integrating an additional n-type interlayer 9 in n-i-p architecture to form a n-i-p-n architecture of perovskite cells without sacrificing initial efficiency. Fig. 7 shows in exemplary embodiments inventive and non-inventive perovskite photovoltaic element 100 with a variation of layer thickness of the n-type interlayer 9 under dry heat aging. The stack of the perovskite photovoltaic elements 100 correspond to that of the working examples. Perovskite photovoltaic elements 100 without n-type interlayer 9 (layer sequence A), with n-type interlayer 9 of layer thickness 10 nm (layer sequence B), of layer thickness 20 nm (layer sequence C) and of layer thickness 30 nm (layer sequence D) are compared under dry heat (85°C). The PCE after 1702 hours dry heat (85°C) was 0,5% for the perovskite cell without n-type interlayer 9 (Fig. 7A), 4,3% with n-type interlayer 9 of 10 nm (Fig. 7B), 5,7% with n-type interlayer 9 of 20 nm (Fig. 7C), and 2,5% with n-type interlayer 9 of 30 nm (Fig. 7D). The stability of perovskite cells also depends on the layer thickness of the n-type interlayer 9 of inventive perovskite cells. Perovskite cells having an n-type interlayer 9 of a layer thickness 10 nm to 30 nm show significantly higher stability under dry heat compared to perovskite cells without n-type interlayer.

Claims

Heliatek GmbH P117WO 27.07.2024 31 / 36 Claims 1. A perovskite photovoltaic element (100), comprising a transparent front electrode (2), a back electrode (12), and a stack (20) arranged between the front electrode (2) and the back electrode (12) having a n-i-p-n architecture with a perovskite photoactive layer (5) as i-layer, comprising in sequence the following layers: a) the transparent front electrode (2); b) a doped or non-doped n-type layer (ETL) (3) comprising an electron transport material (ETM), wherein the LUMO of the n-type layer (3) is equal or less negative than -4.4 eV; c) the perovskite photoactive layer (5) comprising at least an inorganic perovskite or an organic perovskite absorber material; d) a doped or non-doped p-type layer (HTL) (7) comprising a hole transport material (HTM), wherein the HOMO of the p-type layer (7) is equal or more negative than -5.0 eV; e) a n-type interlayer comprising (9) an electron transport material (ETM), wherein the LUMO of the n-type interlayer (9) is equal or more negative than -4.0 eV; e) a metal oxide layer (11); and f) the back electrode (12), wherein the back electrode (12) is formed from a metal or an alloy thereof.

2. The perovskite photovoltaic element (100) according to claim 1, wherein the work-function of the metal oxide layer (11) is 5.0 eV to 7.0 eV (determined by UPS), preferably 6.0 eV to 7.0 eV, or preferably 6.5 eV to 7.0 eV, and / or the material of the metal oxide layer (11) is selected from the group consisting of CrOx, InOx, MoOx, NbOx, NiOx, SnOx, TiOx, VOx, WOx, and ZnOx.

3. The perovskite photovoltaic element (100) according to claim 1 or 2, wherein the LUMO of the n-type interlayer (9) is equal or more negative than -4.2 eV, preferably equal or more negative than -4.4 eV, preferably equal or more negative than -4.5 eV, preferably equal or more negative than -4.6 eV, or preferablyHeliatek GmbH P117WO 27.07.2024 32 / 36 equal or more negative than -4.7 eV, or the LUMO of the n-type interlayer (9) is in the range of -4.0 eV to -6.0 eV, preferably of -4.2 eV to -5.8 eV, preferably of -4.4 eV to -5.8 eV, or preferably of -4.6 eV to -5.8 eV.

4. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the n-type interlayer (9) is a n- doped n-type interlayer (9) comprising a n-dopant, preferably the HOMO of the n-dopant of the n-type interlayer (9) is equal or more negative than -4.6 eV, preferably equal or more negative than -4.8 eV, or the HOMO of the n-dopant of the n-type interlayer (9) is in the range of -4.6 eV to -5.2 eV, preferably of -4.8 eV to -5.2 eV, or preferably of -5.0 eV to -5.2 eV.

5. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the ratio of the n-dopant in the n- type interlayer (9) is 0.1 to 30 vol.-%, preferably 1 to 30 vol.- %, preferably 0.1 to 20 vol.-%, preferably 1 to 20 vol.-%, preferably 0.1 to 10 vol.-%, preferably 1 to 10 vol.-%, preferably 0.1 to 5 vol.-%, or preferably 1 to 5 vol.-%.

6. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the difference between the HOMO of the n-dopant of the n-type interlayer (9) and the LUMO of the ETM of the n-type interlayer (9) is in the range of 0.0 eV to 0.6 eV (by amount), preferably of 0.0 eV to 0.4 eV, preferably of 0.2 eV to 0.4 eV, or preferably of 0.0 eV to 0.2 eV, wherein preferably the HOMO of the n-dopant of the n-type interlayer (9) is more negative compared to the LUMO of the ETM of the n-type interlayer (9).

7. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the HOMO of the p-type layer (7) is equal or more negative than -5.2 eV, preferably equal or more negative than -5.4 eV, or the HOMO of the p-type layer (7) is in the range of -5.2 eV to -5.8 eV, preferably of -5.2 eV to -5.6 eV.Heliatek GmbH P117WO 27.07.2024 33 / 36 8. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the p-type layer (7) is a doped p- type layer (7) comprising a p-dopant, preferably an organic p- dopant, wherein the LUMO of the p-dopant is equal or more negative than -4.0 eV, preferably more negative than -4.5 eV, preferably equal or more negative than -4.7 eV, or preferably equal or more negative than -5.0 eV, or the LUMO of the p-dopant is in the range of -4.0 eV to -5.6 eV, preferably of -4.2 eV to -5.6 eV, or preferably of -4.5 eV to -5.6 eV.

9. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the difference between the HOMO of the p-type layer (7) and the LUMO of the n-type interlayer (9) is 2.0 eV at maximum, preferably 1.5 eV at maximum, or preferably 1.0 eV at maximum, and / or the difference between the HOMO of the p- type layer (7) and the LUMO of the n-type interlayer (9) is in the range of 0.3 eV to 1.2 eV (by amount), preferably of 0.5 eV to 1.0 eV, or preferably of 0.5 eV to 0.8 eV.

10. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the difference between the HOMO of the p-type layer (7) and the LUMO of the n-type interlayer (9) is smaller than the difference between the HOMO of the n-type interlayer (9) and the HOMO of the p-type layer (7), preferably at minimum 0.3 eV (by amount), or preferably at minimum 0.6 eV.

11. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the metal oxide layer (11) has a layer thickness of 5 nm to 50 nm, preferably 10 nm to 30 nm, and / or the n-type interlayer (9) has a layer thickness of 10 nm to 100 nm, preferably 10 nm to 50 nm, preferably 10 nm to 30 nm, preferably 15 nm to 30 nm, or preferably 15 nm to 25 nm.

12. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the electron transport material (ETM) of the n-type interlayer (9) is selected from the group consisting of Hexaazatriphenylen, preferably comprising sixHeliatek GmbH P117WO 27.07.2024 34 / 36 electron-withdrawing groups, Perylenetetracarboxylic dianhydrid (PTCDA) or derivaties thereof, Radialen, Tetracyanobenzochinondimethan, Tetracyanonaphthochinondimethan, Radialen, preferably the electron transport material (ETM) of the n-type interlayer CN-HAT.

13. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein a non-doped n-type layer (4) comprising at least one electron transport material (ETM) is arranged between the n-type layer (3) and the perovskite photoactive layer (5), and / or a non-doped p-type layer (6) comprising at least one hole transport material (HTM) is arranged between the p-type layer (7) and the perovskite photoactive layer (5), wherein preferably the non-doped n-type (4) layer and / or the non-doped p-type layer (6) are directly arranged at the perovskite photoactive layer (5).

14. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the perovskite absorber material of the perovskite photoactive layer (5) is an inorganic perovskite, preferably a three-dimensional halide perovskite, a double perovskite, or a combination thereof, wherein preferably the three-dimensional halide perovskite having a formula ABX, wherein A is selected from Cs, Na, K, Rb, or a combination thereof; B is selected from Pb, Sn, Ge, Cu, Fe, Ga, Eu, Sr, Ti, Mn, Bi, Zn, Mg, Ca, Ba, Y, Yb, Co, In, Sb, Bi, Ag, Ni, Ho, Er, Tb, Sm, La, or a combination thereof; and X is selected from F, Cl, Br, I, or a combination thereof; and wherein preferably the double perovskite having a formula ABCX, wherein A is selected from Cs, Rb, or combination thereof; B is selected from Cu, Ag, Hg, Au, or a combination thereof; C is selected from Sb, Bi, In or a combination thereof; and X is selected from F, Cl, Br, I, or a combination thereof.

15. The perovskite photovoltaic element (100) according to any of the preceding claims, wherein the material of the back electrodeHeliatek GmbH P117WO 27.07.2024 35 / 36 (12) is selected from the group consisting of Al, Au, Ag, Co, Cr, Cu, and Ni, or an alloy thereof.

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