Selective templating growth technique for robust low-dimensional interfaces in perovskite solar cells

Abstract

Herein disclosed is a method for forming an interface layer for an optoelectronic device, the method comprising: forming a template layer on a surface of a perovskite; depositing a solution comprising a bulky cation halide dissolved in an orthogonal solvent directly on the template layer, wherein the solution etches the template layer, which at the same time facilitates intercalation of a bulky cation from the bulky cation halide into the template layer; and annealing the template layer with the solution to form the interface layer. An optoelectronic device comprising the interface layer, and methods for forming the optoelectronic device, are also disclosed.

Description

SELECTIVE TEMPLATING GROWTH TECHNIQUE FOR ROBUST LOW-DIMENSIONAL INTERFACES IN PEROVSKITE SOLAR CELLSCross-Reference to Related Application

[0001] This application claims the benefit of priority of Singapore Patent Application No. 10202500369V, filed 10 February 2025, the content of it being hereby incorporated by reference in its entirety for all purposes.Technical Field

[0002] The present disclosure relates to a method for forming an interface layer for an optoelectronic device. The present disclosure also relates to an optoelectronic device comprising such interface layer, and methods for forming such optoelectronic device.Background

[0003] Low-dimensional (LD) interface engineering may be ubiquitous in the fabrication of perovskite solar cells (PSCs), offering a solution for the trade-off between photovoltaic performance and durability. Traditionally, a relatively stable LD halogenometallate-type material may be capped over a three-dimensional (3D) perovskite layer.

[0004] Particularly, traditional solution-processable methodologies for LD capping layer preparation tend to be based on one of the two approaches: the half-precursor (HP) method (see FIG. 1 A) and the full-precursor (FP) technology (FIG. IB). They may have achieved success in constructing various LD capping materials, such as the traditionally used two-dimensional (2D) perovskite PEAiPbL (PEA, phenethylammonium) and the zero-dimensional halogenometallate PEAiZnXi, wherein X denotes a halogen. However, these methodologies appear to be not universally effective for constructing a wide range of robust LD interfaces with chemically inert bulky cations that may provide intrinsic stability. Traditional examples include the Ruddlesden-Popper (RP) 2D perovskites (NMAjiPbL, (3MTPA)2Pbl4, and (BPMAriPbL (NMA denotes 1- naphthylmethylammonium; 3MTPA denotes 3-(methylthio)propylammonium; BPMA denotes biphenyl-4-yl-methylammonium), as well as the Dion-Iacobson (DI) 2D perovskites (PrEA)Pbl4 and (PiEA)Pbl4 (PrEA denotes 2-pyrrolidin-l-ium-l-ylethylammonium; PiEA denotes 2-piperidin-l-ium-l-ylethylammonium). For such LD capping materials, the traditional half-precursor method may be ineffective due to the relatively low reactivity between 3D perovskites and the inert bulky cations. The full-precursor technology tends to be restricted by the extremely poor solubility (less than 1 mmol L-1for the (PiEA)Pbl4) of the full precursors of these LD capping materials in acetonitrile (ACN), an orthogonal solvent. The engineering of robust LD interfaces with chemically inert bulky cations for 3D perovskites so far still remains an open question.

[0005] There is thus a need to provide for a solution that addresses one or more of the limitations mentioned above.Summary

[0006] In a first aspect, there is provided for a method for forming an interface layer for an optoelectronic device, the method comprising:forming a template layer on a surface of a perovskite;depositing a solution comprising a bulky cation halide dissolved in an orthogonal solvent directly on the template layer, wherein the solution etches the template layer, which at the same time facilitates intercalation of a bulky cation from the bulky cation halide into the template layer; andannealing the template layer with the solution to form the interface layer.

[0007] In another aspect, there is provided for an optoelectronic device comprising:a transparent electrode;a perovskite layer configured between a hole transport layer and an electron transport layer;the interface layer formed according to various embodiments of the first aspect, wherein the interface layer is configured between (i) the perovskite layer and the electron transport layer or (ii) the perovskite layer and the hole transport layer; and a metal electrode distal from the transparent electrode.

[0008] In another aspect, there is provided for a method for forming the optoelectronic device in various embodiments of an aspect mentioned above, the method comprising:providing the transparent electrode;forming the hole transport layer on the transparent electrode;forming the perovskite layer on the hole transport layer;forming the interface layer according to various embodiments of the first aspect and in a manner which renders the interface layer configured between the perovskite layer and the electron transport layer;forming the electron transport layer on the interface layer; andforming the metal electrode on the electron transport layer.

[0009] In another aspect, there is provided for a method for forming the optoelectronic device in various embodiments of an aspect mentioned above, the method comprising:providing the transparent electrode;forming the electron transport layer on the transparent electrode; forming the perovskite layer on the electron transport layer;forming the interface layer according to various embodiments of the first aspect and in a manner which renders the interface layer configured between the perovskite layer and the hole transport layer;forming the hole transport layer on the interface layer; andforming the metal electrode on the hole transport layer.Brief Description of the Drawings

[0010] The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the present disclosure. In the following description, various embodiments of the present disclosure are described with reference to the following drawings, in which:

[0011] FIG. 1A is a schematic diagram showing a solution-processable methodology based on traditional half-precursor (HP) method for fabricating a three-dimensional or two-dimensional bi-layered structure (e.g., the growth of robust Type II LD interfaces on 3D perovskites). IPA denotes 2-propanol. In the context of FIG. 1A, for AXnand Au, A denotes bulky cation, X denotes a halide ion, n may be 1 or 2, and “3D” refers to the 3D perovskite.

[0012] FIG. IB is a schematic diagram showing a solution-processable methodology based on traditional full-precursor (FP) method for fabricating a three-dimensional or two-dimensional bi-layered structure (e.g., the growth of robust Type II LD interfaces on 3D perovskites). ACN denotes acetonitrile. In the context of FIG. IB, for AXnandAn, A denotes bulky cation, X denotes a halide ion, n may be 1 or 2, and “3D” refers to the 3D perovskite.

[0013] FIG. 1C is a schematic diagram showing a solution-processable methodology based on the present method (selective templating growth (STG) technique) for fabricating a three-dimensional or two-dimensional bi-layered structure (e.g., the growth of robust Type II LD interfaces on 3D perovskites). In the context of FIG. 1C, for AXnand An, A denotes bulky cation, X denotes a halide ion, n may be 1 or 2, and “3D” refers to the 3D perovskite.

[0014] FIG. 2A relates to water contact angle analysis. Temporal evolution of water contact angles on the Glass / PEAiPbL film. The films involved were prepared using precursor solutions with identical metal ion concentrations (100 mM in DMF) and the same spin-coating procedure. Compared to the PEAiPbli film of FIG. 2A, the (PiEA)Pbl4 film of FIG. 2B consistently exhibited a larger water contact angle at various time points, indicating that (PiEA)Pbl4 film possesses superior intrinsic water resistance properties.

[0015] FIG. 2B relates to water contact angle analysis. Temporal evolution of water contact angles on the Glass / (PiEA)Pbl4 film. The films involved were prepared using precursor solutions with identical metal ion concentrations (100 mM in DMF) and the same spin-coating procedure. The (PiEA)Pbl4 film consistently exhibited a larger water contact angle compared to the PEA2Pbl4 film of FIG. 2A at various time points, indicating that (PiEA)Pbl4 film possesses superior intrinsic water resistance properties.

[0016] FIG. 2C relates to water contact angle analysis. FIG. 2C shows the statistical analysis of the contact angle values for the films shown in FIG. 2A and FIG. 2B are plotted over time. The films involved in FIG. 2A and FIG. 2B were prepared using precursor solutions with identical metal ion concentrations (100 mM in DMF) and the same spin-coating procedure. The (PiEA)Pbl4 film consistently exhibited a larger water contact angle compared to the PEA2PM4 film at various time points, indicating that (PiEA)Pbl4 film possesses superior intrinsic water resistance properties.

[0017] FIG. 3 A relates to stability against thermal and ambient air conditions. FIG. 3A shows the XRD patterns of the PEA2PM4 film in their initial state and after heating in ambient air for 10 hours and 20 hours. The heat stability tests at 100 °C for the PEA2Pbl4 and (PiEA)Pbl4 films were conducted under ambient conditions (relative humidity 50-60%) without encapsulation. Compared to the (PiEA)Pbl4 film of FIG. 3B, the PEA2Pbl4 film exhibited a notable formation of PbE after just 10 hours of heating in air, indicating the decomposition of PEAiPbL film. This finding further suggests that the (PiEAjPbE film demonstrates superior intrinsic stability against environmental stresses.rooi8i FIG. 3B relates to stability against thermal and ambient air conditions. FIG. 3B shows the XRD patterns of the (PiEAjPbE film in their initial state and after heating in ambient air for 10 hours and 20 hours. The heat stability tests at 100 °C for the PEA2PbE and (PiEAjPbE films were conducted under ambient conditions (relative humidity 50-60%) without encapsulation. Compared to the (PiEA)PbE film, the PEArPbE film of FIG. 3A exhibited a notable formation of PbE after just 10 hours of heating in air, indicating the decomposition of PEA2PbE film. This finding further suggests that the (PiEA)PbE film demonstrates superior intrinsic stability against environmental stresses.

[0019] FIG. 4A relates to characterization of the investigated 3D / 2D structures. FIG.4A shows enlarged XRD patterns of the pristine films of 3D perovskite, template 2D PA2PbE, and target 2D (PiEA)PbE, as well as the stack films of 3D / (PiEA)E, 3D / template 2D, and 3D / target 2D grown from the 3D / template 2D. “3D” refers to the 3D perovskite.

[0020] FIG. 4B shows corresponding ultraviolet-visible absorption spectra of the pristine films of 3D perovskite, template 2D PArPbE, and target 2D (PiEAjPbE, as well as the stack films of 3D / (PiEA)l2, 3D / template 2D, and 3D / target 2D grown from the 3D / template 2D. “3D” refers to the 3D perovskite.

[0021] FIG. 4C shows out-of-plane G1WAXS patterns of the pristine 3D perovskite and the stack films of 3D / (PiEA)E, 3D / template 2D, and 3D / target 2D. “3D” refers to the 3D perovskite.

[0022] FIG. 4D shows SEM image of the pristine 3D perovskite. Scale bar denote 300 nm.

[0023] FIG. 4E shows SEM image of the stack films of 3D / template 2D. Scale bar denote 300 nm.

[0024] FIG. 4F shows stack films of the 3D / target 2D. Scale bar denote 300 nm.

[0025] FIG. 5A shows ¹H NMR spectrum of (PiEA)I₂ with DMSO-d₆ as the solvent.

[0026] FIG. 5B shows ¹H NMR spectrum of (BPMA)I with DMSO-d₆ as the solvent.

[0027] FIG. 6 shows cross-sectional SEM images of the 3D / target 2D-(PiEA)Pbl4 stack film. A thick layer of polystyrene (PS) was deposited on the surface of the 3D / (PiEA)Pbl4 stack film to protect it during sample lamellae preparation by focused ion beam. Note that the white contrast may result from electron accumulation at the interface between the semiconductive capping layer and the insulating PS protective layer.

[0028] FIG. 7 shows Enlarged XRD patterns of the pristine films of 3D perovskite, template 2D PAiPbE, and target 2D (PiEA)Pbl4, as well as the stack films of 3D / (PiEA)12 prepared using (PiEA)h 1PA solution (labeled as 3D / (PiEA)12-lPA) or MeOH solution (labeled as 3D / (PiEA)l2-MeOH), 3D / template 2D-PA2Pbl4, and 3D / targct 2D-(PiEA)Pbl4 grown from the 3D / PA2Pbl / (PiEA)l2-IPA or 3D / PA2PbE / (PiEA)l2-MeOH. Note that consistent results were observed regardless of whether IPA or MeOH was used as the solvent for the (PiEA)l2 solution. “3D” refers to the 3D perovskite.

[0029] FIG. 8 shows photographs of the (PiEA)Pbl4 full-precursor solutions in ACN at various concentrations after stirring for 3 hours at room temperature. A significant amount of red (PiEA)Pbl4 precipitate was observed in the solution, even at a very low concentration of 1 mM, indicating extremely poor solubility of (PiEA)Pbl4 in ACN. This poor solubility makes the full-precursor solution method impractical for fabricating the (PiEA)Pbl4 capping layer.

[0030] FIG. 9 shows in-plane GIWAXS patterns of the pristine 3D perovskite and the stack films of 3D / (PiEA)l2, 3D / template 2D-PA2PM4, and 3D / target 2D-(PiEA)Pbl4 grown from the 3D / template 2D-PA2Pbl.

[0031] FIG. 10A shows XRD patterns of the pristine PA2PM4 film and the PA2Pbl4 / (PiEA)l2-IPA stack film with post-annealing treatment. Note that an airtight sample holder was specially employed to protect the unannealed PA2Pbl4 / (PiEA)l2-IPA sample from potential effects of ambient air.

[0032] FIG. 10B shows XRD patterns of the PA2Pbl4 / (PiEA)l2-IPA stack film without post-annealing treatment. Note that an airtight sample holder was specially employed to protect the unannealed PA2Pbl4 / (PiEA)l2-IPA sample from potential effects of ambient air.

[0033] FIG. 10C shows corresponding UV-Vis absorption spectra of the pristine PA2PbI4film and the PA2Pbl4 / (PiEA)l2-IPA stack films with or without post-annealing treatment. The PA2Pbl4 / (PiEA)l2-lPA stack film subjected to post-annealing treatment exhibited a crystalline (Pi EA jPbl i phase. In contrast, the unannealed stack film revealed a potential amorphous intermediate phase, characterized by a distinct absorption peak below 400 nm.

[0034] FIG. 11A shows XRD patterns of the pristine PA2Pbl4 film, the PA2Pbl4 film treated by spin-coating blank IPA on its surface (labeled as PA2Pbl4 / Blank IPA), and a reference PbE film. The XRD characteristics of the IPA-treated PA2PbIi film closely align with those of the reference Pbl2film, indicating that the blank IPA readily disrupted the structure of PA2PbI by selectively etching out the PA+, leaving behind the parent Pbl2phase.

[0035] FIG. 11B shows corresponding UV-Vis absorption spectra of the pristine PAzPbU film, the PA2PbE film treated by spin-coating blank IPA on its surface (labeled as PAiPbWBlank IPA), and a reference Pbl2film. The absorption characteristics of the IPA-treated PA2Pbl4 film closely align with those of the reference PbE film, indicating that the blank IPA readily disrupted the structure of PA2PM4 by selectively etching out the PA+, leaving behind the parent Pbl2phase.

[0036] FIG. 12A shows XRD patterns of the unannealed PA2Pbl4 / (PiEA)l2-IPA and the unannealed (PiEA)Pbl4-DMF films. Note that the unannealed (PiEA)Pbl4-DMF film was prepared by directly spin-coating a stoichiometric mixture of PbE and (PiEA)I2in DMF without any post-annealing treatment. Given that the XRD characteristics of the unannealed PA2Pbl4 / (PiEA)l2-IPA film are consistent with those of the unannealed (PiEA)Pbl4-DMF film, it is reasonable to deduce that a similar Pbl2-(PiEA)I2intermediate probably formed in the unannealed PA2Pbl4 / (PiEA)I2-IPA film.

[0037] FIG. 12B shows corresponding UV-Vis absorption spectra of the unanncalcd PA2Pbl / (PiEA)l2-IPA and the unannealed (PiEA)Pbl -DMF films. Note that the unannealed (PiEA)Pbl4-DMF film was prepared by directly spin-coating a stoichiometric mixture of Pbl2and (PiEA)I2in DMF without any post-annealing treatment. An amorphous phase with a distinct absorption peak below 400 nm was observed, rather than a traditional mixed phase of PbI₂ and (PiEA)I₂. This indicates the formation of a specific intermediate phase consisting of Pbl2and (PiEA)I2, denoted asthe Pbh-(PiEA)l2 intermediate. Given that the XRD and absorption characteristics of the unannealed PA2Pbl4 / (PiEA)l2-IPA film are consistent with those of the unannealed (PiEA)Pbl4-DMF film, it is reasonable to deduce that a similar Pbl2-(PiEA)12 intermediate probably formed in the unannealed PA2Pbl / (PiEA)l2-IPA film.

[0038] FIG. 13 is a schematic of the potential structure of the Pbl2-(PiEA)l2 intermediate, which consists of a disrupted PhE framework with PiEA2+intercalated within the interlamellar spaces of the layered PbE.

[0039] FIG. 14 shows the potential mechanism underlying the STG technique via an illustration of the underlying structural and compositional evolution governing the STG process for constructing the 3D / target 2D-(PiEA)Pbl4 architecture grown from the 3D / template 2D-PA2PH4 structure, which incorporates two processes: R-OH-induced selective etching of the template’s bulky cation PA+and concurrent intercalation of the target cation PiEA2+.

[0040] FIG. 15A shows1H NMR spectra of the PA2Pbl4 / (PiEA)l2 films with or without IPA washing treatment. The NMR samples were prepared by washing the corresponding PA2Pbl4 / (PiEA)l2 films with an equal amount of DMSO-de. In the NMR spectra, the peaks at approximately 7.2 ppm and 6.9 ppm, characteristic of aromatic protons in PA+, were entirely absent following the IPA washing treatment. This indicates that residual PA+in the films had been completely removed.

[0041] FIG. 15B shows UV-Vis absorption spectra of the PA2PbE / (PiEA)l2 films with or without IPA washing treatment.

[0042] FIG. 16A shows the calculated formation energies of PA2PbI4, PEA2PbI4, and FPEA2Pbl4.

[0043] FIG. 16B shows schematics of corresponding structures of PA2PbI4, PEA2PbI4, and FPEA2PbI4.

[0044] FIG. 17A shows XRD patterns of the pristine PEA2Pbl4 film and the PEA2Pbl4 / (PiEA)l2-IPA stack film without post- annealing treatment.

[0045] FIG. 17B shows the PEA2Pbl4 / (PiEA)l2-IPA stack film with post-annealing treatment.

[0046] FIG. 17C shows corresponding UV-Vis absorption spectra of the pristine PEA2Pbl4 film and the PEA2Pbl4 / (PiEA)l2-IPA stack films without or with postannealing treatment.

[0047] FIG. 18A shows XRD patterns of the pristine FPEA2?bl4 film and the FPEA2PbI4 / (PiEA)l2-IPA stack film without post-annealing treatment.

[0048] FIG. 18B shows the FPEA2PbI4 / (PiEA)12-lPA stack film with post-annealing treatment.

[0049] FIG. 18C shows corresponding UV-Vis absorption spectra of the pristine FPEA₂PbI₄ film and the FPEA₂PbI₄ / (PiEA)I₂-IPA stack films without or with post-annealing treatment.

[0050] FIG. 19A relates to photovoltaic performance of PSCs, showing the statistical distribution of VOCfor 30 individual devices of the control 3D, 3D / template 2D, and 3D / target 2D PSCs. The dotted line, box range, and curved line represent the mean value, standard deviation, and data distribution, respectively. “3D” refers to the 3D perovskite.

[0051] FIG. 19B relates to photovoltaic performance of PSCs, showing JSCfor 30 individual devices of the control 3D, 3D / template 2D, and 3D / target 2D PSCs. The dotted line, box range, and curved line represent the mean value, standard deviation, and data distribution, respectively. “3D” refers to the 3D perovskite.

[0052] FIG. 19C relates to photovoltaic performance of PSCs, showing FF for 30 individual devices of the control 3D, 3D / template 2D, and 3D / target 2D PSCs. The dotted line, box range, and curved line represent the mean value, standard deviation, and data distribution, respectively. “3D” refers to the 3D perovskite.

[0053] FIG. 19D relates to photovoltaic performance of PSCs, showing PCE for 30 individual devices of the control 3D, 3D / template 2D, and 3D / target 2D PSCs. The dotted line, box range, and curved line represent the mean value, standard deviation, and data distribution, respectively. “3D” refers to the 3D perovskite.

[0054] FIG. 19E shows comparison of the current density-voltage (J-V) curves for the champion 3D / targct 2D devices over active areas of 0.06 cm2and 1.235 cm2, measured at room temperature. “3D” refers to the 3D perovskite.

[0055] FIG. 19F shows J-V curves of the 3D / target 2D device measured at various temperatures ranging from 298 K to 175 K. “3D” refers to the 3D perovskite.

[0056] FIG. 19G shows stability tests for the control 3D and 3D / target 2D PSCs under near-MPP operation at 1-sun equivalent white LED illumination in N2. “3D” refers to the 3D perovskite.

[0057] FIG. 19H shows thermal aging tests for the control 3D and 3D / target 2D PSCs at 85 °C in N2. “3D” refers to the 3D perovskite.

[0058] FIG. 20A shows J-V curves of the 3D / target 2D PSC measured in forward and reverse scan directions. “3D” refers to the 3D perovskite.

[0059] FIG. 20B shows stabilized power output of the 3D / targct 2D PSC measured near MPP at a bias of 1.03 V. “3D” refers to the 3D perovskite.

[0060] FIG. 21A shows a photograph of the 3D / target 2D PSC with a relatively large active area of 1.235 cm2. “3D” refers to the 3D perovskite.

[0061] FIG. 2 IB shows statistical distribution of Voc, Jsc, FF, and PCE for 20 individual devices of the 3D / target 2D PSCs with a relatively large active area of 1.235 cm2. The dotted line, box range, and curved line represent the mean value, standard deviation, and data distribution, respectively. “3D” refers to the 3D perovskite.

[0062] FIG. 22 shows normalized TRPL kinetics probed at 790 nm for the control 3D perovskite film and the 3D / target 2D stack film, excited at 690 nm with a low fluence of 13 nJ cm-2. The charge carrier lifetimes were determined by fitting the TRPL kinetics to a single exponential decay. The fitted PL lifetimes for the control 3D perovskite film and the 3D / target 2D stack film are 333 ± 4 ns and 1070 ± 10 ns, respectively. “3D” refers to the 3D perovskite.

[0063] FIG. 23A relates to energy level alignment analysis. FIG. 23A shows UPS spectra showing the secondary electron cut-off region for the control 3D perovskite film and the 3D / target 2D stack film. “3D” refers to the 3D perovskite.

[0064] FIG. 23B relates to energy level alignment analysis. FIG. 23B shows the valence band region for the control 3D perovskite film and the 3D / target 2D stack film.

[0065] FIG. 23C shows the Tauc plots derived from UV-Vis absorption spectra of the control 3D perovskite indicating bandgap of 1.55 eV.

[0066] FIG. 23D shows the Tauc plots derived from UV-Vis absorption spectra of the target 2D perovskite indicating bandgap of 2.20 eV.

[0067] FIG. 23E is a schematic illustration of energy level alignment at the 3D / target 2D interface, showing the formation of an n-N isotype heterojunction. EVac, vacuum level; Ef, Fermi level; Vbi, the resulting additional built-in potential directed from the 2D to the 3D layer; A, the Fermi level difference at the junction. Energy levels are shown in electron volts.

[0068] FIG. 24A relates to thickness analysis. FIG. 24A shows AFM height profile for the Glass / PS stack films, scanning from the blank glass region without the sample to the region with the sample. The height differences (~98 nm) indicate the thicknesses of the pristine PS layer and the stack layer of (PiEA)Ii and PS, respectively. The thickness of the (PiEA)l2 layer can be estimated to be approximately 13 nm by subtracting the thickness of the PS layer from the total thickness of the stack layer consisting of (PiEA)l2 and PS layers. Note that an accurate thickness measurement of the (PiEA)l2 layer directly is challenging due to its relatively small thickness. PS denotes polystyrene.

[0069] FIG. 24B relates to thickness analysis. FIG. 24B shows AFM height profile for the Glass / (PiEA)l2 / PS stack films, scanning from the blank glass region without the sample to the region with the sample. The height differences (~111 nm) indicate the thicknesses of the pristine PS layer and the stack layer of (PiEA)l2 and PS, respectively. The thickness of the (PiEA)l2 layer can be estimated to be approximately 13 nm by subtracting the thickness of the PS layer from the total thickness of the stack layer consisting of (PiEA)l2 and PS layers. Note that an accurate thickness measurement of the (PiEA)h layer directly is challenging due to its relatively small thickness. PS, polystyrene.

[0070] FIG. 25A shows statistical distribution of VOCfor 12 individual PSCs with varying thicknesses of (PiEA)l2, used as a surface passivation molecule for 3D perovskite. The dotted line, box range, and curved line represent the mean value, standard deviation, and data distribution, respectively. Different thicknesses of (PiEA)l2 were achieved by varying the concentration of the (PiEA)l2 deposition solution. Due to the relatively low solubility of (PiEA)I2 in IPA (~10 mM), MeOH was used as the solvent to increase its solubility. A dynamic spin-coating process was employed to deposit the (PiEA)l2 MeOH solution, effectively preventing erosion of the underlying 3D perovskite. One desirable concentration of the (PiEA)l2 solution was found to be 20 mM, resulting in a measured thickness of approximately 13 nm for the (PiEA)l2 layer, as shown in FIG. 24 A and / or FIG. 24B.

[0071] FIG. 25B shows statistical distribution of JSCfor 12 individual PSCs with varying thicknesses of (PiEA)l2, used as a surface passivation molecule for 3D perovskite. The dotted line, box range, and curved line represent the mean value.standard deviation, and data distribution, respectively. Different thicknesses of (PiEA)l2 were achieved by varying the concentration of the (PiEA)l2 deposition solution. Due to the relatively low solubility of (PiEA)I2 in IPA (~10 mM), MeOH was used as the solvent to increase its solubility. A dynamic spin-coating process was employed to deposit the (PiEA)I2 MeOH solution, effectively preventing erosion of the underlying 3D perovskite. One desirable concentration of the (PiEA)I2 solution was found to be 20 mM, resulting in a measured thickness of approximately 13 nm for the (PiEA)I2 layer, as shown in FIG. 24 A and / or FIG. 24B.

[0072] FIG. 25C shows statistical distribution of FF for 12 individual PSCs with varying thicknesses of (PiEAfh, used as a surface passivation molecule for 3D perovskite. The dotted line, box range, and curved line represent the mean value, standard deviation, and data distribution, respectively. Different thicknesses of (PiEA)l2 were achieved by varying the concentration of the (PiEA)l2 deposition solution. Due to the relatively low solubility of (PiEAfh in IPA (~10 mM), MeOH was used as the solvent to increase its solubility. A dynamic spin-coating process was employed to deposit the (PiEA)I2 MeOH solution, effectively preventing erosion of the underlying 3D perovskite. One desirable concentration of the (PiEA)I2 solution was found to be 20 mM, resulting in a measured thickness of approximately 13 nm for the (PiEA)I2 layer, as shown in FIG. 24 A and / or FIG. 24B.

[0073] FIG. 25D shows statistical distribution of PCE for 12 individual PSCs with varying thicknesses of (PiEAfh, used as a surface passivation molecule for 3D perovskite. The dotted line, box range, and curved line represent the mean value, standard deviation, and data distribution, respectively. Different thicknesses of (PiEAfh were achieved by varying the concentration of the (PiEAfh deposition solution. Due to the relatively low solubility of (PiEAfh in IPA (-10 mM), MeOH was used as the solvent to increase its solubility. A dynamic spin-coating process was employed to deposit the (PiEA)I2 MeOH solution, effectively preventing erosion of the underlying 3D perovskite. One desirable concentration of the (PiEAfh solution was found to be 20 mM, resulting in a measured thickness of approximately 13 nm for the (PiEAfh layer, as shown in FIG. 24 A and / or FIG. 24B.

[0074] FIG. 26 shows photographs of 3D perovskite films without a capping layer, with the traditional 2D PEA2Pbh capping layer, or with the target 2D (PiEA)Pbli cappinglayer over time, stored in ambient conditions (relative humidity -50%) without encapsulation at room temperature. The images were taken at the initial time point and at various intervals (Day 16, Day 18, Day 21, Day 23, Day 27, Day 30, Day 42, and Day 62) to evaluate the stability of the films against ambient air erosion. The control 3D perovskite film shows significant degradation starting from Day 16, while the 3D / traditional 2D PFA Pbk film shows degradation starting from Day 23. In contrast, the 3D / target 2D (PiEA)Pbl4 film shows no obvious degradation even at Day 62. This indicates the superior protective effect of the target 2D (PiEAfPbE layer for the 3D perovskite compared to the traditional 2D PE AzPbli layer.

[0075] FIG. 27 shows XRD patterns of the pristine PA2PbI4 and (3MTPA)2PbI4 films, as well as the PA2Pbl4 / (3MTPA)I stack film. The PA2Pbl4 / (3MTPA)I stack film exhibited a crystalline (3MTPA)2Pbl4 phase, indicating the success of the present method (STG technique) in fabricating the 2D (3MTPA)2Pbl4 layer.

[0076] FIG. 28 shows XRD patterns of the pristine PA2PbI4 and (BPMA)2PbI4 films, as well as the PA2Pbl4 / (BPMA)I stack film. The PA2Pbl4 / (BPMA)I stack film exhibited a crystalline (BPMA)2Pbl4 phase, indicating the success of the present method (STG technique) in fabricating the 2D (BPMA)2Pbl4 layer.

[0077] FIG. 29 shows XRD patterns of the pristine PA2PbI4 and (PrEA)PbI4 films, as well as the PA2Pbl4 / (PrEA)l2 stack film. The PA2Pbl4 / (PrEA)l2 stack film exhibited a crystalline (PrEA)Pbl4 phase, indicating the success of the STG technique in fabricating the 2D (PrEA)Pbl4 layer.

[0078] FIG. 30 shows XRD patterns of the pristine PA2SnI4 and (PiEA)SnI4 films, as well as the PA2SnI4 / (PiEA)I2 stack film. The PA2SnI4 / (PiEA)I2 stack film exhibited a crystalline (PiEA)SnI4 phase, indicating the success of the STG technique in fabricating the lead-free 2D (PiEA)Snl4 layer.

[0079] FIG. 31A shows XRD patterns of a pristine PbI2 film and the PbI2 / (PiEA)I2 stack films with post-annealing treatment at 100 °C, 120 °C, or 140 °C for 10 minutes, as well as the PA2Pbl4 / (PiEA)l2 stack film based on the present method (STG technique) with post-annealing treatment at 100 °C for 10 minutes. Note that the amount of (PiEA)l2 was kept consistent on top of both the Pbh film and the PA2PbI4 template by using the same spin-coating process and the same concentration of the (PiEA)l2 solution to ensure a fair comparison. As a result, under the same post-annealingtreatment at 100 °C for 10 minutes used in the STG technique, no obvious target (PiEA)Pbl4 phase was detected in the Pbl2 / (PiEA)l2 stack film. It is to note it is possible to rule out the possibility of an insufficient amount of the initial PbI2, as PbI2 was still detected after the post-annealing treatment. This indicates that the (PiEA)I2 salt does not readily react with the pristine PbI2 film to form the target (PiEA)PbI4, highlighting the advantages of the STG technique. Although a small amount of the target (PiEA)Pbl4 phase was detected in the Pbl2 / (PiEA)l2 stack film with post-annealing treatment at a relatively higher temperature of 140 °C, the amount was significantly less than that produced using the present method, as deduced from the much weaker XRD and absorption signals of the target (PiEA)Pbl4 phase in the as-prepared PbI2 / (PiEA)I2 stack film.

[0080] FIG. 31B shows the enlarged XRD patterns of FIG. 31A of the Pbl2 / (PiEA)l2 stack films with post-annealing treatment at 100 °C, 120 °C, or 140 °C for 10 minutes.

[0081] FIG. 31C shows corresponding UV-Vis absorption spectra of a pristine PbI2 film and the PbI2 / (PiEA)I2 stack films with post-annealing treatment at 100 °C, 120 °C, or 140 °C for 10 minutes, as well as the PA2PbI4 / (PiEA)I2 stack film based on the present method (STG technique) with post-annealing treatment at 100 °C for 10 minutes. Note that the amount of (PiEA)I2 was kept consistent on top of both the PbI2 film and the PA2PbI4 template by using the same spin-coating process and the same concentration of the (PiEA)I2 solution to ensure a fair comparison. As a result, under the same post-annealing treatment at 100 °C for 10 minutes used in the STG technique, no obvious target (PiEA)PbI4 phase was detected in the PbI2 / (PiEA)I2 stack film. It is to note it is possible to rule out the possibility of an insufficient amount of the initial PbI2, as PbI2 was still detected after the post-annealing treatment. This indicates that the (PiEA)I2 salt does not readily react with the pristine PbI2 film to form the target (PiEA)PbI4, highlighting the advantages of the STG technique. Although a small amount of the target (PiEA)PbI4 phase was detected in the PbI2 / (PiEA)I2 stack film with post-annealing treatment at a relatively higher temperature of 140 °C, the amount was significantly less than that produced using the present method, as deduced from the much weaker XRD and absorption signals of the target (PiEA)PbI4 phase in the as-prepared PbI2 / (PiEA)I2 stack film.

[0082] FIG. 32 is a schematic of the 3D / target 2D PSC device structure, wherein: FTO denotes fluorine-doped tin oxide; SAM denotes self-assembled monolayer; 3D in FIG.32 refers to a layer of Cs0.15FA0.85Pb2.8Cl0.2; 2D in FIG. 32 refers to a layer of (PiEA)Pbl4; PCBM denotes [6,6]-phenyl-C6i-butyric acid methyl ester; BCP denotes bathocuproinc.Detailed Description

[0083] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the present disclosure may be practiced.

[0084] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0085] The present disclosure relates to a method for forming an interface layer for an optoelectronic device, and such optoelectronic devices. The interface layer can be formed as a low-dimensional interface in an optoelectronic device, e.g., a perovskite solar cell device. Such low-dimensional interface, i.e., the interface layer, may be deemed two-dimensional (2D).

[0086] Advantageously, the method of the present disclosure, referred to herein as the present method, introduces a selective templating growth (STG) technique (see FIG.1C), which enables the growth of a wide range of robust low-dimensional (LD) interfaces with chemically inert bulky cations on three-dimensional (3D) perovskite surfaces, providing enhanced intrinsic stability. As such, the present method may be referred to as “STG technique”, “STG process”, STG strategy”, etc. The present method may be an advancement unattainable with traditional methodologies. The present method offers a significant step forward in LD interface engineering, with the potential to develop more efficient and stable perovskite solar cells (PSCs).

[0087] Low-dimensional (LD) interfaces formed via the present method can have high-stability, chemically inert bulky cations, and offer great potential to resolve the tradeoff between efficiency and stability in perovskite solar cells. Traditionally, a significant gap persists in achieving such LD interfaces due to the low reactivity of bulky cations and solubility constraints of their precursors in orthogonal solvents compatible with three-dimensional perovskites. The present method, however, is able to overcome this challenge by involving a selective templating growth strategy that leverages on metastable low-dimensional interfaces as templates to drive the growth of more stable low-dimensional interfaces through a meticulously developed organic cation exchange process. One example prototype of perovskite solar cells having an interface formed via the present method can achieve impressive efficiencies of up to 25.1% over an active area of 1.235 cm2- among the highest reported for traditional 1-cm2perovskite solar cells. Such perovskite solar cells also exhibit exceptional stability, retaining over 93% and 98% of their initial efficiency after 1,000 hours of operation and 1,100 hours of thermal aging at 85 °C, respectively. The versatility of the present method was also demonstrated via significantly expanding interface material options to a wide range of such robust low-dimensional interfaces, paving the way for the development of more efficient and stable perovskite solar cells.

[0088] Advantageously, the interface layer formed via the present method can be a lowdimensional capping layer on a perovskite-based layer that not only passivates the surface defects of the perovskite layer, but also protects it from environmental stresses (e.g., as oxygen, moisture, light, and heat).

[0089] Advantageously, the present method provides for a solution-processable selective templating growth technique for constructing a wide range of robust lowdimensional interfaces with chemically inert bulky cations on 3D perovskite surfaces, providing enhanced intrinsic stability. The present method is demonstrated in the examples section of the present disclosure, such as via a PSCs device incorporating a robust LD interface material formed via the present method, and the examples also highlight the potential applicability of the present method in other perovskite-based optoelectronic devices, such as light-emitting diodes (LEDs), lasers, and photodetectors, etc.

[0090] As mentioned above, the present method offers a unique solution-processable STG technique for growth of robust 2D interfaces on 3D perovskite surfaces. As a nonlimiting example, via the present method, a metastable 2D overlayer of PA2PbI4 (PA denotes phenylammonium) can be strategically engineered on 3D perovskite surfaces to serve as a template (see FIG. 1C). This 2D template effectively facilitates the subsequent growth of the robust 2D interface, AnPbI4, through an organic cation exchange between the template’s bulky cation, PA+, and the target bulky cation, An+, trigged by alcohol-induced selective etching of P A+and concurrent intercalation of AI1+.

[0091] Advantageously, the present method renders enhanced PSC device performance by involving a robust 2D interface formed via the present method. According to the STG technique of the present method, for example a robust 2D interface of (PiEA)Pbl4, grown from a 2D template of PA2PbI4, can be successfully fabricated as a capping layer (or referred to in the present disclosure as “target” layer) on a 3D perovskite surface. Microscopic examination revealed that such robust 2D interface can induce effective synergistic effects of chemical passivation and field-effect passivation for 3D perovskites. As a result, PSCs with such robust 2D interface achieved a champion efficiency of 25.6% (certified at 25.0%) over an active area of 0.06 cm2and 25.1% for -1 cm2cells at room temperature. An impressive efficiency exceeding 27% was obtained at a low temperature of 215 K. The PSCs having an interface layer formed from the present method also exhibited good stability under both operational and thermal stress conditions.

[0092] Moreover, unlike the traditional HP method, in the present method involving the STG technique, the chemically inert bulky cation An+no longer needs to react directly with the underlying 3D perovskite layer, a process hampered by their low reactivity. Instead, An+interacts with the underlying metastable 2D template (e.g., of PA2PbI4), enabling the formation of the robust 2D interface of AnPbI4 due to the more favourable reactivity between An+and the metastable template. Additionally, unlike the traditional FP method, the present method involving the STG technique eliminates the need for full precursor solutions for forming the robust 2D interface materials, which are constrained by their extremely poor solubility in acetonitrile, which is one of the preferred orthogonal solvents. Therefore, the present method with the STG technique offers an advantageous access to the growth of a wide range of robust LD interfaceswith chemically inert bulky cations on 3D perovskite surfaces, providing enhanced intrinsic stability — an advancement unattainable with aforesaid traditional methods. This provides greater materials flexibility for LD interface engineering, unlocking opportunities to develop more stable LD interfaces, leading to more efficient and durable PSCs.

[0093] As one non-limiting example, just to aid understanding, the method may be used to fabricate the robust 2D interface, such as (PiEA)PbI4, may involve a 2D template of PA2PbI4initially deposited onto a 3D perovskite surface by dynamically spin-coating its full-precursor solution in acetonitrile (e.g., 25 mM) at 3,000 r.p.m. for 30 seconds. Next, the target bulky cation iodide, (PiEA)I2, dissolved in alcohol (e.g. 31.25 mM in methanol), was dynamically spin-coated onto the pre-formed PA2PbI4layer at 3,000 r.p.m. for 30 seconds, followed by annealing at 100 °C for 10 minutes. Finally, the prepared films were washed twice by spin-coating with 2-propanol (IPA) at 5,000 r.p.m. for 30 seconds to remove any residual PAI and (PiEA)I2.

[0094] The present disclosure also provides for optoelectronic devices involving such interface layer, and methods for forming such optoelectronic devices. It follows that the optoelectronic devices and methods for forming the optoelectronic devices have the advantages conferred by the interface layer formed from the present method, as the optoelectronic devices and methods for forming the optoelectronic devices involves aforesaid interface layer and the method of the present disclosure for making the interface layer. For brevity, the interface layer may be referred to herein as an “interface”.

[0095] Details of various embodiments of the interface layer, methods, and optoelectronic devices, and advantages associated with the various embodiments are now described below and / or with reference to the drawings. Where advantages of the embodiments and features are already demonstrated in one or more examples of the examples section herein further below and / or in the drawings, they shall not be reiterated for brevity.

[0096] In the present disclosure, there is provided for a method for forming an interface layer for an optoelectronic device, the method may comprise forming a template layer on a surface of a perovskite, depositing a solution that may comprise a bulky cation halide dissolved in an orthogonal solvent directly on the template layer, wherein thesolution may etch the template layer, which at the same time may facilitate intercalation of a bulky cation from the bulky cation halide into the template layer, and annealing the template layer with the solution to form the interface layer (i.e., the target layer). The method is advantageous, as it enables formation of robust low-dimensional (Type II) interfaces using chemically inert bulky cations that do not react away / dcstroy 3D perovskites, overcomes the low reactivity limitation of traditional half-precursor (HP) methods and avoids the poor solubility constraint of full-precursor (FP) methods in orthogonal solvents (e.g. ACN). The present method offers a solution-processable route compatible with delicate 3D perovskite layers, and enables controlled organic cation exchange via a metastable template, leading to higher crystallinity and interface quality.

[0097] In various embodiments, forming the template layer may comprise providing a precursor solution comprising a precursor salt dissolved in an organic solvent, wherein the organic solvent does not react with the perovskite, and depositing the precursor solution on the surface of the perovskite. Advantageously, this helps in that any underlying 3D perovskite does not get dissolved or damaged during a template layer deposition, and provides a uniform and conformal “starting interface”, improving reproducibility.

[0098] In various embodiments, the precursor salt may comprise an organic-inorganic hybrid metal halide, which comprises an ammonium halide having a formula (A1)(X2)nand a metal halide having a formula M^X1)^, wherein: A1may be an ammonium cation having a structure of R1-NH3+, wherein R1may include an optionally substituted C4-12 alkyl, an optionally substituted C3-12 cycloalkyl, or an optionally substituted arylalkyl, M1may comprise at least one ion being an element from any one of group 2, group 3, group 7 to group 13, or group 15 of the Periodic Table, X1and X2may be a halide ion, z may be 1, 2 or 3, n may be 1, 2 or 3, and a may be 1, 2 or 3. This may help to facilitate selective etching while preserving the mctal-halidc framework. The term “arylalkyl” includes within its meaning, a chemical moiety containing both an aliphatic and an aromatic ring structure, e.g., an aryl group connected to a parent structure (a molecule) via an alkyl chain, rather than being directly attached through the aromatic ring. Nonlimiting examples of arylalkyl, for the purpose of providing an understanding and not to limit this term, may include phenylmethyl, 2-phenylethyl, 3-phenylpropyl, etc.

[0099] In various embodiments, the precursor salt may comprise phenylammonium lead iodide, butylammonium lead iodide, propylammonium lead iodide, ethylammonium lead iodide, naphthylmethylammonium lead iodide, phenethylammonium lead iodide, phenylmethylammonium lead iodide, or 4-fluoro-phenethylammonium lead iodide.

[0100] In various embodiments, the organic solvent may comprise acetonitrile, acetone, methanol, t-butyl alcohol, ethanol, isopropyl alcohol, tetrahydrofuran, or methylamine.

[0101] In various embodiments, depositing the solution directly on the template layer may comprise mixing a precursor of the bulky cation and a precursor of a halide in the orthogonal solvent to form the solution.

[0102] In various embodiments, the precursor of the bulky cation may comprise 2-pyrrolidin- 1-yl-ethylamine, 2-piperidin- 1-yl-ethylamine, biphenyl-4-yl-methylamine, 3-(methylthio)propylamine, 4-tert-butylbenzylamine, 1-aminopyrene, or 3,4,5-trifluoroaniline. Advantageously, these precursors enable formation of lowdimensional interface layers (e.g., Type II) with superior stability that are not accessible or easily accesible using traditional HP and FP methods.

[0103] In various embodiments, the precursor of the halide may comprise hydroiodic, hydrobromic, or hydrochloric acid. These are advantageous, as it helps in formation of the bulky cation halide salts, and can help in compatibility with a metal-halide framework formation.

[0104] In various embodiments, the orthogonal solvent may comprise acetonitrile, acetone, methanol, t-butyl alcohol, ethanol, isopropyl alcohol, tetrahydrofuran, or methylamine. The term “orthogonal solvent”, in the present disclosure, refers to a solvent selected such that it may be capable of dissolving or processing a subsequently deposited material, while being substantially or completely non-solvcnt to an underlying material, thereby preventing dissolution, degradation, or intermixing of the underlying layer during fabrication.

[0105] In various embodiments, the bulky cation halide has a formula (A2)(X3)m, wherein: A2may be an ammonium cation having a structure of R2-NHb+or NHb+-R2-NHb+, wherein R2may include an optionally substituted C4-12 alkyl, an optionally substituted C3-12 cycloalkyl, or an optionally substituted arylalkyl, X ’ is a halide ion; mmay be 1, 2 or 3, and b may be 1, 2 or 3. These bulky cation halides may aid in formation of both Ruddlesden-Popper type and Dion-Jacobson type interface layers.

[0106] In various embodiments, the bulky cation may comprise 2-pyrrolidin-l-ium-1 -ylethylammonium, 2-piperidin- 1 -ium- 1 -ylethylammonium, biphenyl-4-yl-methylammonium, 3-(methylthio)propylammonium, 4-tert-butyl-benzylammonium, 1-pyrenammonium, or 3,4,5-trifluoroanilinium.

[0107] In various embodiments, the annealing may be carried out at a temperature range of 80°C to 130°C, 90°C to 130°C, 100°C to 130°C, 110°C to 130°C, 120°C to 130°C, 80°C to 90°C, 80°C to 100°C, 80°C to 110°C, 80°C to 120°C, etc. Such temperatures may prevent thermal damage to the perovskite layers and enable controlled crystallization of the interface layer.

[0108] The present disclosure also provides for an optoelectronic device. Embodiments and advantages described for the method in various embodiments of the first aspect can be analogously valid for the present optoelectronic devices subsequently described herein, and vice versa. As the various embodiments and advantages have already been described above and in the examples section herein further below, they shall not be iterated for brevity.

[0109] In various embodiments, the optoelectronic device may comprise a transparent electrode, a perovskite layer configured between a hole transport layer and an electron transport layer, the interface layer formed according to various embodiments of the first aspect, wherein the interface layer may be configured between (i) the perovskite layer and the electron transport layer or (ii) the perovskite layer and the hole transport layer; and a metal electrode distal from the transparent electrode. Advantageously, with an interface layer formed from the method described in various embodiments of the first aspect, the optoelectronice device having such interface layer can have improved charge extraction efficiency due to graded energy alignment across such stack, reduced non-radiative recombination at the perovskite interfaces, higher power conversion efficiency (PCE), and improved device reproducibility owing to well-defined layer sequence. With the interface layer, the optoelectronic device, and methods for forming such optoelectronic device, are versatile in the device architecture (n-i-p or p-i-n) to be configured (i.e., improves device architecture freedom).

[0110] In various embodiments, the interface layer may comprise a thickness in a range of 20 nm to 60 nm, 30 nm to 60 nm, 40 nm to 60 nm, 50 nm to 60 nm, 20 nm to 30 nm, 20 nm to 40 nm, 20 nm to 50 nm, etc.

[0111] In various embodiments, the interface layer may be crystalline, which may help improve carrier transport across an interface layer, offers thermal and ambient stability, and may reduce trap-assisted recombination.

[0112] In various embodiments, the interface layer may be defined by: at least one X-ray diffraction peak at 20 in a range of 4° to 10°, 5° to 10°, 6° to 10°, 7° to 10°, 8° to 10°, 9° to 10°, etc., and / or at least one excitonic absorption peak in a range of 300 nm to 600 nm, 400 nm to 600 nm, 500 nm to 600 nm, 300 nm to 400 nm, 300 nm to 500 nm, etc. These features may help to facilitate quality control and reproducibility.

[0113] The present disclosure further provides for a method for forming the optoelectronic device described in various embodiments of one or more aspects mentioned above. Embodiments and advantages described for the method in various embodiments of the first aspect and for the optoelectronic device can be analogously valid for the present method subsequently described herein, and vice versa. As the various embodiments and advantages have already been described above and in the examples section herein further below, they shall not be iterated for brevity.

[0114] In various embodiments, the method may comprise: providing the transparent electrode, forming the hole transport layer on the transparent electrode, forming the perovskite layer on the hole transport layer, forming the interface layer according to the method of various embodiments of the first aspect and in a manner which renders the interface layer configured between the perovskite layer and the electron transport layer, forming the electron transport layer on the interface layer, and forming the metal electrode on the electron transport layer. The optoelectronic device from such method may be a n-i-p device (n: n-type layer for extracting electrons; i: intrinsic perovskite layer for absorbing light and generate carriers; p: p-type layer for extracting holes). With the interface layer, such method (and hence the optoelectronic device from such method) may minimize interfacial defects and preserves interface integrity.

[0115] The present disclosure further provides for a method for forming the optoelectronic device described in various embodiments of one or more aspects mentioned above. Embodiments and advantages described for the method in variousembodiments of the first aspect and for the optoelectronic device can be analogously valid for the present method subsequently described herein, and vice versa. As the various embodiments and advantages have already been described above and in the examples section herein further below, they shall not be iterated for brevity.

[0116] In various embodiments, the method may comprise: providing the transparent electrode, forming the electron transport layer on the transparent electrode, forming the perovskite layer on the electron transport layer, forming the interface layer according to the method of various embodiments of the first aspect and in a manner which renders the interface layer configured between the perovskite layer and the hole transport layer, forming the hole transport layer on the interface layer, and forming the metal electrode on the hole transport layer. The optoelectronic device from such method may be a n-i-p device. With the interface layer, such method (and hence the optoelectronic device from such method) may minimize interfacial defects, enables integration with inverted architectures, and preserves interface integrity.

[0117] The term “optionally substituted” means a chemical compound or moiety can be substituted or non-substituted, i.e., may or may not bear one or more substituents.

[0118] The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the present disclosure.

[0119] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0120] In the context of various embodiments, the tilde symbolthe term “about”, and the term “approximately”, as applied to a numeric value encompasses the exact value and a reasonable variance. The variance may be ±20%, ±10%, ±5%, ±1 %, ±0.5%, ±0.1%, etc.

[0121] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0122] Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.Examples

[0123] Interface engineering may be ubiquitous in perovskite optoelectronic devices, particularly in perovskite solar cells (PSCs), offering an effective solution to the tradeoff between device performance and stability. One of the most extensively studied interface materials may be organic ammonium / sulfonium salts, comprising an organic bulky cation paired with a halide anion. The bulky cations may be categorized into two main types based on their reactivity with the underlying three-dimensional (3D) perovskites. Type I includes low-stability or highly reactive bulky cations that react with 3D perovskites to form low-dimensional (LD) interfaces (e.g., an interface layer), referred to as Type I LD interfaces, such as phenethylammonium (PEA+) and n-butylammonium (BA+). Such interfaces generally exhibit improved conductivity compared to related insulating organic salts but often suffer from compromised stability due to their high reactivity. Type II, in contrast, consists of high-stability or chemically inert bulky cations, which may be less prone to react with 3D perovskites to form LD interfaces. Examples may include 3 -(methylthio )propylammonium (3MTPA+), biphenyl-4-yl-methylammonium (BPMA+), 2-pyrrolidin- 1-ium- 1-ylethylammonium (PrEA2+), and 2-piperidin-l-ium- 1-ylethylammonium (PiEA2+). These cations are predominantly been used as insulating organic salt interfaces due to their low reactivity; however, their poor conductivity has significantly limited their effectiveness. Given the limitations of both Type I LD interfaces and insulating organic salt interfaces, the most promising interfaces are likely LD interfaces incorporating high-stability Type II bulky cations, referred to as Type II LD interfaces or robust LD interfaces, which provide both excellent conductivity and high stability.

[0124] Despite their clear potential, a significant gap persists in achieving Type II LD interfaces, primarily due to the lack of effective growth methodologies. The commonly used half-precursor (HP) and full-precursor (FP) approaches, though successful in constructing numerous Type I LD interfaces, are less suitable for Type II LD interfaces. Specifically, the traditional HP method proves ineffective due to the extremely low reactivity of Type II bulky cations with 3D perovskites (FIG. 1 A). Additionally, the FP approach is often constrained by the poor solubility of Type II LD interface material precursors in acetonitrile (ACN), the preferred orthogonal solvent for this method (FIG.IB). The present method addresses this gap, enabling the advantageous development of advanced Type II LD interfaces, potentially driving further advancements in perovskite optoelectronic devices.

[0125] Herein, such critical gap is addressed by a strategy that leverages metastable LD interfaces as templates to drive the growth of more stable LD interfaces through a favorable organic cation exchange process. The selective templating growth (STG) technique (FIG. 1C) effectively overcomes the key limitations of traditional methods, eliminating the need for reactivity between Type II bulky cations and 3D perovskites in the HP method, as well as the requirement for full precursor ACN solutions of Type II LD interface materials in the FP method. As a result, the prototype PSCs incorporating Type II LD interfaces demonstrate an impressive efficiency of up to 25.1% over an active area of 1.235 cm2, which, to the best of knowledge, is among the highest efficiencies reported for 1-cm2PSCs. These PSCs also exhibit excellent stability under both operational and thermal stress conditions, retaining more than 93% and 98% of their initial efficiencies after 1,000 hours of operation and 1,100 hours of thermal aging at 85 °C, respectively.

[0126] The method for forming the interface layer, optoelectronic devices involving such interface layer, and methods for making such optoelectronic devices, are described in further details, by way of non-limiting examples, as set forth below.

[0127] Example 1: Selective templating growth (STG) technique

[0128] The method of the present disclosure, i.e., STG technique, is illustrated in FIG.1C. The STG process begins with the deposition of a metastable two-dimensional (2D) perovskite layer of PA2PM4 (PA, phenylammonium) onto the 3D perovskite surface. This metastable layer is strategically engineered to serve as a template for the subsequent growth of a more stable target Type II LD interface. Notably, PA2PbI4has been identified as an example template for this process, with further details discussed in subsequent sections. The target Type II bulky cations (An+, where A represents PrEA, PiEA, BPMA, etc., and n may equal 1 or 2), dissolved in alcohols (R-OH, where R can be methyl, ethyl, or isopropyl), are then spin-coated onto the PA2PbI4template. Through alcohol-induced selective etching of the template’s bulky cation PA+and concurrent intercalation of the target bulky cation An+, an overall organic cation exchange occursbetween PA+and An+, culminating in the formation of the target Type 11 LD interface, AnPbI4.

[0129] Example 2: Materials and Methods

[0130] All of the chemicals and materials involved in the various examples were purchased and used as received unless specified otherwise. The patterned ITO and FTO-coated glass substrates (sheet resistance <15 sq-1) were purchased from Shenzhen Huayu Union Technology Co., Ltd. and Suzhou Shangyang Solar Technology Co., Ltd, respectively. PbI2(99.99%) and [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACZ) were purchased from Tokyo Chemical Industry Co., Ltd. (2-(4-(bis(4-methoxyphenyl)amino)phenyl)-l-cyanovinyl)phosphonic acid (MPA-CPA) was purchased from Luminescence technology Corp. Formamidinium iodide (FAI), phenylammonium iodide (PAI), phenethylammonium iodide (PEAI) and 2-pyrrolidin-l-ium-l-ylethylammonium iodide [(PrEA)I2] were purchased from Greatcell Solar Ltd. C60(99.9%) was purchased from Puyang Yongxin Fullerene Technology Co., Ltd. BCP (99.9%) and phenyl-C61-butyric acid methyl ester (PCBM) were purchased from Yingkou Shangsheng Business Co., Ltd. PbCl2(99.999%), SnI2(99.999%), Csl (99.999%), Hl (47 wt% in water), N. N-dimethylformamide (DMF, 99.8%, anhydrous), dimethyl sulfoxide (DMSO, 99.9%, anhydrous), 1,2 -dichlorobenzene (DCB, 99%, anhydrous), isopropanol (IPA, 99.5%, anhydrous), ethanol (99.5%, anhydrous), methanol (MeOH, 99.8%, anhydrous) and acetonitrile (ACN, 99.8%, anhydrous) were purchased from Sigma-Aldrich. 2-piperidin-1 -yl-ethylamine and 4-biphenylmethyl amine were purchased from Innochem Science & Technology Co., Ltd. 3-(methylthio)propylammonium iodide [(3MTPA)I] was purchased from Xi'an Yuri Solar Co. Ltd.

[0131] Synthesis of 2-piperidin-l-ium-l-ylethylammonium iodide [(PiEA)I2] and 4-biphenylmethylammonium iodide [(BPMA)I].

[0132] (PiEA)I2was prepared by introducing hydroiodic acid (HI, 47 wt% in water) into a solution of 2-piperidin- 1 -yl-ethylamine in ethanol at around 0 °C, maintaining a molar ratio of amine to HI of 1:2.5. The mixture was stirred in an ice-water bath for two hours and then at room temperature overnight. Afterward, the solvent was slowly evaporated under reduced pressure to yield the crude product. The crude product was then dissolved in ethanol and recrystallized by gradually adding diethyl ether. Theresulting small crystals were washed several times with diethyl ether and subsequently dried in a vacuum oven at 60 °C overnight. Finally, the dried crystals were transferred into a nitrogen-filled glove box for further use. (BPMA)l was synthesized similarly to that for (PiEA)l2. The synthesized (PiEA)l2 and (BPMA)I were confirmed through their1H NMR spectra, which are consistent with theoretical predictions, as shown in FIG.5 A and FIG. 5B.

[0133] Fabrication of prototype 2D interface layers based on the present method (STG technique).

[0134] To fabricate the prototype 2D (PiEA)Pbl interface layer, the template 2D PA2PbI4was initially deposited onto the 3D perovskite surface by dynamically spincoating its full-precursor (FP) solution in ACN at 3,000 r.p.m. for 30 seconds (1,500 r.p.m. was used for characterization samples to enhance signal quality). Following this, the (PiEA)I2solution in alcohol was spin-coated onto the pre-formed PA2PbI4layer at 3,000 r.p.m. for 30 seconds (1,500 r.p.m. for characterization samples), followed by annealing at 100 °C for 10 minutes. It is to note that the solubility of (PiEA)l2 in IPA is around 10 mmol L-1(mM) but increases to approximately 50 mM in MeOH. When IPA was used as the solvent, the (PiEA)I2solution was prepared at nearly its saturated concentration of 10 mM, and the corresponding PA2PbI4FP solution was prepared at a concentration of 8 mM. The concentration ratio of the (PiEA)l2 solution to the PA2PbI4FP solution was maintained slightly above stoichiometric at 1.25, ensuring an excess of 25% (PiEA)l2. This excess ensures the complete conversion of the PA2PbI4layer to the target (PiEA)PbI4layer, with any residual (PiEA)l2 being removed through a final IPA washing treatment. The thickness of the target (PiEA)Pbl4 interface layer may be limited by the relatively low solubility of (PiEA)I2in IPA. However, this limitation was readily resolved when MeOH is used as the solvent due to its higher solubility for (PiEA)I2. Thereafter, one desirable thickness of the (PiEA)Pbl4 interface layer was found to be approximately 40 nm (as shown in FIG. 6). This was achieved using a 25 mM PA2PbI4FP solution and a corresponding 31.25 mM (PiEA)I2MeOH solution, maintaining the same 25% excess as mentioned earlier. A dynamic spin-coating process was employed to deposit the (PiEA)I2 MeOH solution to minimize potential erosion of the underlying 3D perovskite. Consistent results were observed when MeOH was used as the solvent compared to IPA (FIG. 7). Finally, the prepared films were washed twiceby spin-coating with IPA at 5,000 r.p.m. for 30 seconds to remove any residual PAI and (PiEA)l2. The other 2D interface layers based on the STG technique were prepared using similar procedures.

[0135] Device fabrication.

[0136] The patterned ITO or FTO-coated glass substrates were cleaned using an ultrasonic bath in the following sequence: first with an aqueous detergent solution, then with deionized water, followed by acetone, and finally with ethanol, each step lasting for approximately 20 minutes. Subsequently, the substrates were treated with ultraviolet ozone for 15 minutes prior to use. All spin-coating procedures were carried out in a nitrogen-filled glovebox (Ch < 10 ppm, H2O < 1 ppm). The hole-transporting layer (MeO-2PACZ or MPA-CPA) was deposited by spin-coating the corresponding solution (0.5 mg mL-1in ethanol) onto the cleaned substrates at a speed of 3,000 r.p.m. for 30 seconds, followed by annealing at 100°C for 10 minutes. The 3D perovskite (Cs0.15FA0.85PbI2.8Cl0.2) precursor solution contained 580.9 mg PbI2, 38.9 mg PbCl2, 204.7 mg FAI, and 54.6 mg CsI, dissolved in 1 mL of mixed solvent of anhydrous DMF and DMSO (4:1, v / v). The 3D perovskite films were deposited by spin-coating the precursor solution at 1,000 r.p.m. for 10 seconds (5-second ramp) and then at 4,000 r.p.m. for 45 seconds (1-second ramp). Approximately 160 pL of DCB was rapidly dropped onto the substrates 10 seconds before the end of the spin-coating program. The films were then annealed at 100°C for 10 minutes. Next, the target 2D (PiEA)PbI4 interface layer was fabricated on top of the prepared 3D perovskite layer based on the STG technique as mentioned above. Then an electron-transporting layer of PCBM was deposited by spin-coating a 10 mg mL-1PCBM chlorobenzene solution at 2,000 r.p.m. for 30 seconds, followed by the thermal evaporation of a 25 nm layer of Ceo under a vacuum <5.0x l0-4Pa. Finally, a 6 nm BCP and a 100 nm silver were thermally evaporated under a vacuum <5.0 x 10-4Pa through a metal shadow mask, resulting in an active area of 0.060 cm2for small-area devices or 1.235 cm2for large-area devices. To reduce possible reflections and mitigate potential edge effects, a 100 nm layer of LiF was evaporated onto the glass side of the substrates, serving as an anti-reflection coating. Additionally, a non-reflective black metal aperture mask was attached to the glass side of the substrates, with an aperture area of approximately 0.040 cm2for smallarea devices and 1.009 cm2for large-area devices, as needed. For stability tests, theMeO-2PACZ layer, PCBM / Ceo layer, and silver electrode in the PSCs were replaced with an MPA-CPA layer, a thicker PCBM layer prepared by spin-coating a 20 mg mL-1PCBM chlorobenzene solution at 2,000 r.p.m., and a chromium / gold (5 nm / 100 nm) electrode, respectively.

[0137] Device characterization.

[0138] The current density-voltage (J-V) characteristics of the PSCs were measured using a Keithley 2400 source meter under simulated AM 1.5 G solar illumination provided by a ScienceTech UHE-NSC AAA solar simulator. The solar simulator's effective irradiance for the PSCs was calibrated to one sun (100 mW cm-2) using an Oriel PV Reference Cell System (91150V), accounting for any potential spectral mismatch. The J-V curves were obtained in either forward or reverse scan direction, ranging from -0.2 V to 1.25 V or from 1.25 V to -0.2 V, at a scanning rate of approximately 0.5 V s-1. Unless otherwise specified, the reported J-V curves were recorded in the reverse scan direction at room temperature inside a nitrogen-filled glovebox (Ch < 10 ppm, H2O < 1 ppm).

[0139] Other characterizations.

[0140] The water contact angle analysis was measured using a Dataphysics OCA 15 Contact Angle Goniometer. The X-ray diffraction (XRD) patterns were collected using a D8 Advance X-ray diffractometer (Cu Ka, 2 = 1.5418 A, 40 kV, 30 mA). Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) patterns were obtained using Xenocs Nano-inXider system. Note that due to detector configuration, the Xenocs Nano-inXider provides GIWAXS data at various angles between the X-ray beam and the sample, rather than capturing the entire pattern. The incident X-ray wavelength was 1.54189 A, and the X-ray beam was set at an incident angle of 0.3°. The ultraviolet-visible (UV-Vis) absorption spectra were recorded using a Shimadzu UV3600PLUS UV-Vis-NIR spectrophotometer. The nuclear magnetic resonance (NMR) spectra were collected using AVANCE II NEO 400 MHz Spectrometer (BRUKER), the samples were dissolved in the DMSO-de solvent. The planar scanning electron microscopy (SEM) images were taken on a JEOL JSM-7600F microscope. The cross-sectional sample and corresponding SEM image were prepared and acquired using a ZEISS Crossbeam 540 focused ion beam (FIB)-SEM system. The ultraviolet photoelectron spectroscopy (UPS) analysis was performed using a Kratos AXIS Supra spectrometerequipped with a standard helium-discharge lamp emitting He 1 photons (21.22 eV). Time-resolved photoluminescence (TRPL) measurements were conducted using a time-correlated single -photon counting (TCSPC) system (PicoHarp 300). The samples were excited at 690 nm with a low fluence of 13 nJ cm-2. The atomic force microscopy (AFM) analysis was conducted on a Bruker Bioscope Resolve system.

[0141] Stability tests.

[0142] The operational stability test for the studied PSCs was carried out in a N2-filled glovebox (O2 < 10 ppm, H2O < 1.0 ppm). The test was performed near the maximum power point (MPP) under illumination from a white light-emitting diode (LED) lamp with an equivalent effective irradiance of one sun, where the measured short-circuit current density (JSC) matched that measured under simulated AM 1.5 G solar illumination. The device performance was periodically evaluated. Target 1 and Target 2 represent the prototype PSCs of 3D / 2D (PiEAjPbL and 3D / 2D (3MTPA)2PbI4, respectively. The initial power-conversion efficiencies (PCEs) for the control 3D, Target 1, and Target 2 PSCs were 19.5%, 22.6%, and 22.0%, respectively. For thermal stability tests, the PSCs were heated at 85 °C in a N2-filled glovebox (O2 < 10 ppm, H2O < 1.0 ppm), with performance assessments conducted at regular intervals. The initial PCEs for the control 3D, Target 1, and Target 2 PSCs were 19.3% ±0.1%, 22.6% ± 0.3%, and 22.0% ± 0.1%, respectively, each representing the average from three individual devices.

[0143] Density functional theory (DFT) calculation.

[0144] For calculation of total energies of the 2D perovskites PA2PbI4, PEA2PbI4, and FPEA2PbI4, along with their constituting fragments PAI, PEAI, FPEAI, and Pbh, DFT calculations were employed using the Vienna Ab initio Simulation Package (VASP). The Generalized Gradient Approximation (GGA) functional, developed by Perdew, Burke, and Ernzerhof, was used to account for the electron-ion and electron-electron interactions. The Projector Augmented Wave (PAW) method, as implemented in VASP, was used to describe the outermost electrons, specifically for Pb (5d106s26p2), I (5s25p5), F (2s22p5), N (2s22p3), C (2s22p2), and H (1 s1). A Gaussian smearing width of 0.05 eV was applied for Brillouin-zone integration, achieving an energy convergence criterion of 10-5eV per atom. Lattice and ionic relaxations were performed using a conjugate-gradient method, with forces kept below 0.005 eV A-1. A consistent plane-wave energy cutoff of 550 eV was used, and well-converged k-meshes were employed for accurate total energy calculations.

[0145] Example 3A: Discussion on Fabrication and characterization of prototype Type II LD interfaces

[0146] 2D (PiEA)Pbl4 (CCDC number: 1841683) was selected as one of the prototypes of Type II LD interfaces for a detailed investigation to elucidate the underlying principles and advantages of the present method. This was motivated by the superior intrinsic stability of (PiEA)Pbl4 against environmental stresses compared to the traditional 2D (PEA)2PbI4(FIG. 2A to FIG. 2C and FIG. 3 A and FIG. 3B). Furthermore, (PiEA)Pbl4 exhibits extremely poor solubility in ACN (less than 1 mmol L-1, FIG. 8), rendering the traditional FP technology inapplicable. In the first stage of the STG process, a distinctive X-ray diffraction (XRD) peak at 29 = 6.5° (FIG. 4A) and an excitonic absorption peak near 500 nm (FIG. 4B) were observed in the 3D / PA2Pbl4 stack film. These findings align with those observed in the pristine PA2Pbl4 film, confirming that the template 2D PA2Pbl4 was successfully formed and retained its original structure on the 3D perovskite surface during this stage. Following the deposition of (PiEA)l2onto the PA2PbI4 template and post-treatment, the characteristic XRD and excitonic absorption peaks of PA2Pbl4 vanished. Concurrently, a new XRD peak at 29 = 8.5° (FIG. 4A) and an excitonic absorption peak around 545 nm (FIG. 4B) emerged, corresponding to those observed in the pristine (PiEA)Pbl4 film. These changes indicate that the metastable PA2PM4 template likely underwent an organic cation exchange reaction with (PiEA)I2, where PA+is replaced by PiEA2+, leading to the formation of the more stable target 2D (PiEA)PbL. In contrast, in the 3D / (PiEA)I2stack film prepared by the traditional HP method, no characteristic XRD or excitonic absorption peaks associated with (PiEA)Pbl4 were observed (FIG. 4A and FIG. 4B), indicating negligible chemical reactivity between the 3D perovskite and (PiEA)I2, hindering formation of the desired 2D phase.

[0147] It was then evaluated the potential preferential orientation in the as-prepared 2D (PiEA)Pbl4 interface layer using grazing incidence wide angle X-ray scattering (GIWAXS). As predicted, no distinct diffraction patterns were observed in the low scattering vector (q) range (q < 0.8 A-1) in either out-of-plane or in-plane directions in the 3D / (PiEA)I2stack film (FIG. 4C and FIG. 9). The only exception was a Debye-Scherrer ring pattern observed at q > 0.8 A-1, characteristic of polycrystalline 3D perovskite. This indicates that no LD components were formed in the 3D / (PiEA)I2 stack film, in accordance with the aforementioned XRD analysis results. Interestingly, while LD components in most reported 3D / LD stack films fabricated by other methodologies exhibit sharp Bragg spots in the out-of-plane GIWAXS patterns, the 2D (PiEA)Pbl4 component in the as-prepared 3D / target 2D stack film features a characteristic semiBragg ring (FIG. 4C). This reveals that the as-prepared 2D (PiEA)PbI4 component likely has mixed, though not completely random, orientations, including both out-of-plane and in-plane directions relative to the substrate. This was further verified by the relatively weak yet distinctive semi-Bragg ring in the corresponding in-plane GIWAXS pattern (FIG. 9). It should be noted that the partial in-plane orientation incorporated in the less ordered 2D (PiEA)Pbl4 interface layer is more favorable for charge transport compared to a widespread, highly ordered out-of-plane orientation. Additionally, scanning electron microscopy (SEM) images (FIG. 4D to FIG. 4F) revealed that the surface of the 3D perovskite was effectively covered by the 2D (PiEA)PbI4 interface layer, as indicated by the substantially uniform surface morphology that differs from the control 3D perovskite after the STG process. This was further corroborated by the cross-sectional SEM image of the 3D / target 2D stack film (FIG. 6). Moreover, the grain size of the 3D perovskite remained nearly unchanged throughout the STG process, indicating negligible corrosion of the 3D perovskite film induced by the procedure.

[0148] Example 3B: Discussion on Mechanism of Present Method (STG

[0149] To elucidate the underlying mechanism of the STG technique, a comprehensive investigation into the structural and compositional evolution from the template 2D PA2PbI4 to the target 2D (PiEA)Pbl4 during the STG process was conducted. It was discovered that depositing the (PiEA)l2 2-propanol (IP A) solution onto the PA2PbI4 template, without any post-annealing treatment, did not result in the anticipated bi-layered PA2Pbl4 / (PiEA)l2 structure. Instead, an intermediate structure was produced, which transitions into the target (PiEA)Pbl4 upon post-annealing treatment (FIG. 10). This is evidenced by the disappearance of the characteristic XRD and excitonic absorption peaks of PA2PbI4, which is observed if the bi-layered PA2Pbl4 / (PiEA)l2 structure had formed. Instead, an amorphous phase emerges with adistinct absorption peak below 400 nm prior to the formation of (PiEA)PbI4 (FIG. 10A to FIG. 10C). To clarify the possible formation process of the intermediate structure, it was first investigated the potential impact of pure IPA solvent on the PA2PbI4 template by directly spin-coating it on top. The results indicate that the structure of PA2PbI4 is readily disrupted by the blank IPA solvent through selective etching of PA+, leaving behind PbI2 (FIG. 11A and FIG. 11B). Therefore, an IPA-induced selective etching process of PA+likely occurs during the deposition of the (PiEA)I2 IPA solution onto the PA2PbI4 template. Expectedly, this etching process generates an intermediate structure comprising a mixed phase of PbI2, produced by IPA-induced selective etching of PA+, and the freshly deposited (PiEA)l2, which effectively exhibit the XRD and absorption characteristics of PbI2. However, given that the observed XRD and absorption characteristics of the intermediate structure arc significantly different from those of Pbh, it can be ruled out the possibility that the intermediate structure is a mixed phase of PbI2 and (PiEA)I2. It is thus speculated that another process, namely PiEA2+intercalation, probably occurs simultaneously with the selective etching of PA+, leading to the formation of a PbI2-(PiEA)I2 intermediate phase. This inference was further validated by the observation that the XRD and absorption characteristics of the intermediate phase in the STG process closely match those of a specific PbI2-(PiEA)I2 intermediate phase, which was intentionally prepared by directly spin-coating a stoichiometric mixture of PbI2 and (PiEA)I2 in N,N-dimethylformamide without any post-annealing treatment (FIG. 12A and FIG. 12B). Unfortunately, due to the amorphous nature of the PbI2-(PiEA)I2 intermediate phase, it was difficult to determine its exact structure through single crystal growth. However, based on a structure of a similar intermediate phase, MAI-Pbh-DMSO (MA, methylammonium; DMSO, dimethyl sulfoxide), it is reasonable to speculate that the PbI2-(PiEA)I2 intermediate phase likely comprises a similarly disrupted Pbh framework with PiEA2+intercalated within the interlamellar spaces of the layered Pbh, as shown in FIG. 13.

[0150] To conclude, the underlying structural and compositional evolution governing the STG process for constructing the 3D / target 2D-(PiEA)Pbl4 architecture can be outlined in four primary stages, as shown in FIG. 14. Initially, the 3D / template 2D-PA2PbI4stack is prepared by directly depositing 2D PA2PbI4 onto 3D perovskite. Next, a 3D / PbI2-(PiEA)I2 intermediate stack, along with PAI and (PiEA)h residuals, formsas a consequence of two pivotal processes: R-OH-induced selective etching of the template’s bulky cation PA+and concurrent intercalation of the target cation PiEA2+, triggered by the subsequent deposition of the (PiEA)I2 R-OH solution. Then, the 3D / target 2D-(PiEA)Pbl4 stack, along with PAI and (PiEA)l2 residuals, forms by converting the PbI2-(PiEA)I2 intermediate into the target (PiEA)Pbl4 through postannealing treatment. Finally, the purified 3D / target 2D-(PiEA)Pbl4 stack is obtained by removing the PAI and (PiEA)I2 residuals through IPA washing treatment.

[0151] Notably, the complete removal of the residual PAI is evidenced by the disappearance of nuclear magnetic resonance signals characteristic of aromatic protons in the relevant films following the IPA washing treatment (FIG. 15A). Although confirming the removal of residual (PiEA)I2 is challenging due to the interference of PiEA2+in the target (PiEA)Pbl4, it is reasonable to deduce that residual (PiEA)I2 is also eliminated along with residual PAI, given the solubility of both pristine PAI and (PiEA)I2 in IPA. The formed target 2D (PiEA)Pbl4 structure is also found to be structurally resistant to the IPA washing treatment, as evidenced by the nearly consistent absorption characteristics of the as-prepared (PiEA)Pbl4 film before and after the IPA washing treatment (FIG. 15B).

[0152] It can be underscored that the intrinsic metastability of 2D PA2PbI4, designated as the template, is for the effective execution of the STG process. To clarify this, it was evaluated the feasibility of using other 2D perovskites, PEA2Pbl4 and FPEA2PbI4(FPEA, 4-fluoro-phenethylammonium), as templates. These perovskites exhibit relatively higher intrinsic stabilities, inferred from their lower calculated formation energies (FIG. 16A and FIG. 16B). Unlike PA2PbI4, the (PiEA)l2 IPA solution can only partially etch PEA+from PEA2Pbl4 and even less FPEA+from FPEA2PbI4, as evidenced by the persistent characteristic XRD and excitonic absorption signals of PEA2Pbl4 and FPEA2PbI4after depositing (PiEA)I2 onto these templates (FIG. 17A to FIG. 17C and FIG. 18A to FIG. 18C). This limited etching is likely attributed to the relatively higher intrinsic stabilities of PEA2Pbl4 and FPEA2PbI4compared to PA2PbI4. In the PEA2PbI4 template system (FIG. 17A to FIG. 17C), it was found that the residual XRD and excitonic absorption signals of PEA2Pbl4 vanished after post- annealing treatment, yet the expected XRD and absorption characteristics of the target (PiEA)Pbl4 did not manifest. Instead, multiple XRD peaks at 29 < 7° and blue-shifted absorption featuresemerge, likely due to the formation of complex LD structures incorporating hybrid cations of PEA+and PiEA2+. Conversely, no similar phenomena were observed in the case of FPEA2PbI4 template system (FIG. 18A to FIG. 18C). The residual XRD and excitonic absorption signals of FPEA2PbI4persist after post-annealing treatment. Additionally, the detection of weak but distinguishable XRD and absorption characteristics of the target (PiEA)PbI4 suggests minor formation, consistent with the observed slight etching of FPEA+. Accordingly, metastable 2D PA2PM4 is preferred as the template for the STG process over the relatively more stable 2D PEA2PbI4and FPEA2PbI4.

[0153] Example 4: An Example of Prototype Perovskite Solar Sells Including an Interface Layer of the Present Disclosure

[0154] To validate the applicability of the present STG technique, 3D / target 2D PSCs with a p-i-n architecture was fabricated: glass / indium tin oxide or fluorine-doped tin oxide / [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid / 3D Cs0.15FA0.85PbI2.8Cl0.2(FA, formamidinium) / target 2D / [6,6]-phenyl-C61-butyric acid methyl ester / C60 / bathocuproine / silver. The target 2D interface layer is referred to as (PiEA)Pbl4 unless specified otherwise. For comparison, control PSCs without a 2D interface layer and 3D / template 2D-PA2Pbl4 PSCs were also investigated. Statistical analysis of device performance (FIG. 19A to FIG. 19D) reveals a negligible increase in power-conversion efficiency (PCE) from 19.8% ± 0.5% to 20.5% ± 0.3% upon incorporating the 2D template, and a significant enhancement to 25.1% ± 0.2% with the target 2D interface layer. This considerable improvement is primarily attributed to the substantial increase in open-circuit voltage (Voc) from 1.042 ± 0.019 V to 1.204 ± 0.005 V. The 3D / target 2D device can achieve a PCE of 25.6%, with a Voc of 1.200 V, a fill factor (FF) of 85.2%, and a short-circuit current density (Jsc) of 25.0 mA cm-2over a small active area of 0.06 cm2(FIG. 19E). These results are in close agreement with the values independently verified by the national Solar Energy Research Institute of Singapore, which recorded a Voc of 1.196 V, an FF of 84.2%, a Jsc of 24.8 mA cm-2, and a PCE of 25.0%, measured using a high-precision solar simulator with an almost ideal spectral mismatch factor of 1.01 for one example of device of the present disclosure (SERIS provides a high-precision solar simulator with an almost ideal spectral mismatch factor of approximately 1.01 for the PSCs. The verified PCE isaround 25.0% in the reverse scan direction and 24.3% in the forward scan direction, based on a non-reflective black aperture with a certified area of 0.04834 cm2). The 3D / target 2D PSCs also exhibited negligible hysteresis, with a stabilized power output of 25.0% measured near the maximum power point (MPP) (FIG. 20A and FIG. 20B), and an outstanding PCE of 25.1% over a relatively larger active area of 1.235 cm2, with a Voc of 1.198 V, an FF of 83.3%, and a Jsc of 25.2 mA cm-2(FIG. 19E and FIG. 21A and Fig. 21B). A remarkable PCE of 27.1%, with a Voc of 1.261 V, an FF of 82.5%, and a Jsc of 26.0 mA cm-2, was recorded at a low temperature of 215 K (FIG. 19F), indicating potential applications of the PSCs in near-space and polar regions. To the best of knowledge, this is the first report of a PCE exceeding 27% for PSCs measured under simulated 1-sun (100 mW cm-2) AM 1.5 G solar illumination, even though the measurements were conducted at a relatively low temperature. The observed trend in device performance at low temperatures is consistent with research findings.

[0155] In accordance with most findings from studies on 2D interface layers, the enhanced photovoltaic performance of the 3D / target 2D PSCs primarily results from the synergistic effects of chemical passivation and field-effect passivation induced by the target 2D interface layer. This is substantiated by a significant increase in photoluminescence lifetime from 333 ± 4 ns to 1070 ± 10 ns (FIG. 22), as well as the formation of a favorable 3D / 2D n-N isotype heterojunction with an additional built-in potential (Vbi) directed from the 2D to the 3D layer upon the introduction of the target 2D interface layer (FIG. 23A to FIG. 23E). It is also noted that the thickness (-40 nm) of the target 2D interface layer (FIG. 6) is relatively larger than that of most traditionally reported 2D interface layers, which may have a thickness below 20 nm. This tolerance for thicker interface layer is likely due to the partial in-plane orientation of the target 2D interface layer, as demonstrated above, which is more favorable for charge transport. Since the additional Vbican be dependent on the thickness of the 2D interface layer at the 3D / 2D n-N isotype heterojunction, the relatively large thickness of the present target 2D interface layer can augment the additional Vbi, thereby enhancing device performance more effectively. In line with most reports, an example thickness of the pristine, chemically inert, bulky ammonium salt (PiEA)I2, used as a surface passivation molecule, is much smaller (-13 nm, as indicated in FIG. 24A to FIG. 24B and FIG. 25A to FIG. 25D) due to its intrinsic insulating property. Although a largerthickness can ensure more effective passivation, as indicated by the further improved Voc, the resulting poor conductivity may cause a significant drop in FF, thereby reducing the PCE (FIG. 25A to FIG. 25D).

[0156] The potential stability improvement provided by the target 2D interface layer was also evaluated. As predicted, the target 2D interface layer offers significantly better protection for the 3D perovskite against ambient air erosion compared to the traditional 2D PEA2Pbl4 interface layer (FIG. 26), likely due to its superior intrinsic stability, as demonstrated above. Moreover, the 3D / target 2D PSCs exhibit excellent stability under both operational and thermal stress conditions. For the best-performing 3D / target 2D PSCs, more than 93% and 98% of the initial PCEs were retained after 1,000 hours of near-MPP operation under white light-emitting diode (LED) illumination with an effective irradiance equivalent to 1 sun (FIG. 19G), and 1,100 hours of thermal aging at 85 °C in a nitrogen-filled glovebox (FIG. 19H).

[0157] Example 5: Summary Discussion

[0158] The present method (STG strategy) significantly expands the interface options for 3D perovskites to a wide range of highly promising, robust Type II LD materials incorporating high-stability, chemically inert bulky cations. This was previously unattainable due to the low reactivity of these bulky cations and the solubility constraints of the Type II LD material precursors in orthogonal solvents compatible with 3D perovskites. While the 2D (PiEA)PbI4 is comprehensively demonstrated here as a prototype to demonstrate the principles and advantages of the STG technique, various other superior Type II LD interface materials can be compatible and used with the present approach. These include not only Pb-based candidates, such as (3MTPA)2Pbl4(FIG. 27), (BPMA)2Pbl4(FIG. 28), and (PrEA)PbI4 (FIG. 29), but also lead-free alternatives, such as (PiEA)SnI4 (FIG. 30). It is noteworthy that a traditional vacuum evaporation-assisted two-step hybrid method has been shown to successfully grow the specific 2D (HBzA)2PbI4(HBzA, 4-hydroxybenzylammonium) on 3D perovskites. However, extending this method to robust Type II LD interface materials may present challenges, as the findings indicate that the (PiEA)I2salt does not readily react with a pristine Pbl2film to form the target (PiEA)Pbl4, even at elevated temperatures of up to 140 °C (FIG. 31 A to FIG. 31C). It is also to be highlighted thatthe STG technique offers a cost-effective, fully solution-processable methodology that avoids the need for vacuum deposition of toxic PbI2.

[0159] Various examples of the present method demonstrate the method advantageous for growing a low-dimensional (LD) interface on a 3D perovskite surface, the method including: depositing a metastable LD overlayer dissolved in a first orthogonal solvent on a 3D perovskite surface to serve as a template layer, depositing a target bulky cation halide (e.g., chloride, bromide and iodide) dissolved in a second orthogonal solvent on the metastable LD overlayer; and annealing the resultant structure to induce reaction between the target bulky cation halide with the underlying metastable LD overlayer to form the target LD interface.

[0160] In various examples, the metastable LD overlayer can include an organic-inorganic hybrid metal halide, consisting of a metal halide having a formula M1(X1)zand an ammonium halide having a formula (A1)(X2)n, wherein M1is at least one ion of one or more group 2, group 3, group 7, group 8, group 9, group 10, group 11, group 12, group 13 or group 15 elements of the Periodic Table of Elements, or any mixture thereof; A1is an ammonium cation having a structure of R1-NH3+, wherein R1is an optionally substituted C4 to C12 alkyl, an optionally substituted C3 to C12 cycloalkyl, an optionally substituted arylalkyl, or any mixture thereof; X1and X2can be a halide ion or any mixture thereof; z can be 1, 2 or 3, n can be 1, 2 or 3; a can be 0 or an integer of 1, 2 or 3.

[0161] In various examples, the first and second orthogonal solvents may be independently selected from the group consisting of acetonitrile (ACN), acetone, dimethylformamide (DMF), dimethylsulfoxide (DMSO), methanol, t-butyl alcohol, ethanol, isopropyl alcohol, tetrahydrofuran, methylamine and any mixture thereof.

[0162] In various examples, a target bulky cation halide can have a formula (A‘)(X3)m, wherein A2is an ammonium cation having a structure of R2-NHb+or NHb+-R2-NHb+, wherein R2is an optionally substituted C4 to C12 alkyl, an optionally substituted C3 to C12 cycloalkyl, an optionally substituted arylalkyl, or any mixture thereof; X3is a halide ion or any mixture thereof; m is 1, 2 or 3; b is 0 or an integer of 1, 2 or 3.

[0163] In various examples, a 3D perovskite compound layer is demonstrated, which includes a 3D perovskite compound having a formula (A3)M2(X4)3 wherein: A3may be selected from the group consisting of at least one ion of one or more group 1 elementsof the Periodic Table of Elements, an organic cation having a structure of R3-(NHx)y+wherein R3may be CH or alkyl, x may be 2 or 3 and y may be 1 or 2, as valency allows, and any mixture thereof; M2may be at least one ion of one or more group 14 elements of the Periodic Table of Elements or any mixture thereof; and X4may be a halide ion or any mixture thereof.

[0164] In various examples, the metastable LD overlayer can be prepared by spincoating, blade-coating, slot-die coating, spray coating and inkjet printing a solution of the metastable LD overlayer on the 3D perovskite surface.

[0165] In various examples, the target bulky cation halide can be prepared by spincoating, blade-coating, slot-die coating, spray coating and inkjet printing a solution of the target bulky cation halide on the metastable LD overlayer.

[0166] In various examples, the metastable LD overlayer may be selected from the group consisting of phenylammonium (PA) lead iodide (PA2PbI4), phenethylammonium (PEA) lead iodide (PEA2PbI4), n-butylammonium (BA) lead iodide (BA2PbI4), phenylmethylammonium (PMA) lead iodide (PMA2PbI4), 1-naphthylmethylammonium (NMA) lead iodide (NMA2PbI4), 4-fluoro-phenethylammonium (FPEA) lead iodide (FPEA2PbI4), and any mixture thereof.

[0167] In various examples. A2in the formula (A2)(X3)mmay be selected from the group consisting of 2-pyrrolidin-l-ium-l-ylethylammonium (PrEA), 2-piperidin-l-ium-l-ylethylammonium (PiEA), biphenyl-4-yl-methylammonium (BPMA), 3-(methylthio)propylammonium (3MTPA), 4-tert-butyl-benzylammonium (tBBA), 1-pyrenammonium (PRA), 3,4,5-trifluoroanilinium (345FAn), and any mixture thereof.

[0168] Example 6: Advantages and Commercial Applications

[0169] The present method is applicable to a wide range of robust LD interface materials with chemically inert bulky cations. The findings in the examples demonstrated the potential to open pathways for designing and developing superior robust LD interfaces with chemically inert bulky cations, offering enhanced protection for 3D perovskite surfaces and resulting in more efficient and durable PSCs. Beyond the 2D interface of (PiEA)PbI4, a variety of robust LD interface materials can be developed using the STG technique, including (PrEA)PbI4, (PiEA)SnI4, (BPMA)2PbI4. (3MTPA)2PbI4, etc.

[0170] The present method and interface layer from the present method are applicable to perovskite optoelectronic devices beyond solar cells. The findings in the examples are not only applicable to the PSC devices, but also understandably applicable to other perovskite optoelectronic devices such as LEDs, lasers, sensors, etc.

[0171] The present method (STG technique) and interface layer can find potential commercial applications in optoelectronic devices, such as perovskite-type solar cells, light-emitting diodes, lasers, sensors, etc.

[0172] While the present disclosure has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims. The scope of the present disclosure is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

1. CLAIMS1. A method for forming an interface layer for an optoelectronic device, the method comprising:forming a template layer on a surface of a perovskite;depositing a solution comprising a bulky cation halide dissolved in an orthogonal solvent directly on the template layer, wherein the solution etches the template layer, which at the same time facilitates intercalation of a bulky cation from the bulky cation halide into the template layer; andannealing the template layer with the solution to form the interface layer.

2. The method of claim 1, wherein forming the template layer comprises:providing a precursor solution comprising a precursor salt dissolved in an organic solvent, wherein the organic solvent does not react with the perovskite; and depositing the precursor solution on the surface of the perovskite.

3. The method of claim 2, wherein the precursor salt comprises an organic -inorganic hybrid metal halide, which comprises an ammonium halide having a formula (A1)(X2)nand a metal halide having a formula M1(X1)z, wherein:A1is an ammonium cation having a structure of R1-NH3+, wherein R1includes an optionally substituted C4- 12 alkyl, an optionally substituted C3-12 cycloalkyl, or an optionally substituted arylalkyl;M1comprises at least one ion being an element from any one of group 2, group 3, group 7 to group 13, or group 15 of the Periodic Table;X1and X2are a halide ion;z is 1, 2 or 3;n is 1, 2 or 3; anda is 1, 2 or 3.

4. The method of claim 2 or 3, wherein the precursor salt comprises phenylammonium lead iodide, butylammonium lead iodide, propyl ammonium lead iodide, ethylammonium lead iodide, naphthylmethylammonium lead iodide.phenethylammonium lead iodide, phenylmethylammonium lead iodide, or 4-fluoro-phenethylammonium lead iodide.

5. The method of any one of claims 2 to 4, wherein organic solvent comprises acetonitrile, acetone, methanol, t-butyl alcohol, ethanol, isopropyl alcohol, tetrahydrofuran, or methylamine.

6. The method of any one of claims 1 to 5, wherein depositing the solution directly on the template layer comprises mixing a precursor of the bulky cation and a precursor of a halide in the orthogonal solvent to form the solution.

7. The method of claim 6, wherein the precursor of the bulky cation comprises 2-pyrrolidin- 1-yl-ethylamine, 2-piperidin- 1-yl-ethylamine, biphenyl-4-yl-methylamine, 3-(methylthio)propylamine, 4-tert-butylbenzylamine, 1-aminopyrene, or 3,4,5-tri fluoroaniline.

8. The method of claim 6 or 7, wherein the precursor of the halide comprises hydroiodic, hydrobromic, or hydrochloric acid.

9. The method of any one of claims 1 to 8, wherein the orthogonal solvent comprises acetonitrile, acetone, methanol, t-butyl alcohol, ethanol, isopropyl alcohol, tetrahydrofuran, or methylamine.

10. The method of any one of claims 1 to 9, wherein the bulky cation halide has a formula (A2)(X3)m, wherein:A2is an ammonium cation having a structure of R2-NHb+or NHb+-R2-NHb+, wherein R2includes an optionally substituted C4-12 alkyl, an optionally substituted C3-12 cycloalkyl, or an optionally substituted arylalkyl;X3is a halide ion;m is 1, 2 or 3; andb is 1, 2 or 3.

11. The method of any one of claims 1 to 10, wherein the bulky cation comprises 2-pyrrolidin- 1 -ium- 1 -ylethylammonium, 2-piperidin- 1 -ium- 1 -ylethylammonium, biphenyl-4-yl-methylammonium, 3-(methylthio)propylammonium, 4-tert-butyl-benzylammonium, 1-pyrenammonium, or 3,4,5-trifluoroanilinium.

12. The method of any one of claims 1 to 11, wherein the annealing is carried out at a temperature range of 80°C to 130°C.

13. An optoelectronic device comprising:a transparent electrode;a perovskite layer configured between a hole transport layer and an electron transport layer;the interface layer formed according to any one of claims 1 to 12, wherein the interface layer is configured between (i) the perovskite layer and the electron transport layer or (ii) the perovskite layer and the hole transport layer; anda metal electrode distal from the transparent electrode.

14. The optoelectronic device of claim 13, wherein the interface layer comprises a thickness in a range of 20 nm to 60 nm.

15. The optoelectronic device of any one of claims 13 or 14, wherein the interface layer is crystalline.

16. The optoelectronic device of any one of claims 13 to 15, wherein the interface layer is defined by:at least one X-ray diffraction peak at 2θ in a range of 4° to 10°; and / or at least one excitonic absorption peak in a range of 300 nm to 600 nm.

17. A method for forming the optoelectronic device of any one of claims 13 to 16, the method comprising:providing the transparent electrode;forming the hole transport layer on the transparent electrode;forming the perovskite layer on the hole transport layer;forming the interface layer according to the method of any one of claims 1 to 12 and in a manner which renders the interface layer configured between the perovskite layer and the electron transport layer;forming the electron transport layer on the interface layer; andforming the metal electrode on the electron transport layer.

18. A method for forming the optoelectronic device of any one of claims 13 to 16, the method comprising:providing the transparent electrode;forming the electron transport layer on the transparent electrode; forming the perovskite layer on the electron transport layer;forming the interface layer according to the method of any one of claims 1 to 12 and in a manner which renders the interface layer configured between the perovskite layer and the hole transport layer;forming the hole transport layer on the interface layer; andforming the metal electrode on the hole transport layer.

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