Two-dimensional perovskite templates for durable and efficient perovskite solar cells and optoelectronic devices

Abstract

The present disclosure provides a method of forming a perovskite film, the method comprising depositing an ink onto a substrate and annealing the substrate to form the perovskite film. The ink comprises: one or more 2D perovskite crystals; one or more first group cations or ammonium halides; one or more metal halides; and one or more solvents. A perovskite ink comprises one or more 2D perovskite crystals, one or more first group cations or ammonium halides, one or more metal halides, and one or more solvents.

Description

[0001] Statement on Federally Funded Research This invention was carried out with government support under license number DE-EE0008843 granted by the U.S. Department of Energy. The government holds certain rights to this invention. Background Technology

[0002] With perovskite solar cells (PSCs) already outperforming commercially available silicon solar cells, the next step forward is to obtain perovskite materials with high intrinsic environmental, thermal, and light stability. FAPbI3 3D perovskite has recently become a focus of attention due to its low bandgap (1.48 eV) approaching the Shockley–Queisser limit. However, FAPbI3 3D perovskite exhibits temperature-dependent polymorphic properties, making its use in its pure form undesirable. Therefore, various additives have been used to stabilize 3D FAPbI3 perovskite, including small organic cations (e.g., cesium, rubidium, methylammonium), larger bulk cations (e.g., phenylethylammonium, ethylenediaminetetraacetic acid), and nanomaterials (e.g., lead sulfide, lead iodide, cesium). However, using these additives often results in an increased bandgap (1.53–1.55 eV) compared to the optimal bandgap (1.48 eV). Furthermore, these additives introduce multiple degradation pathways, thereby reducing the intrinsic material and device stability. Therefore, a perovskite composition with minimal degradation pathways is needed to improve overall material and device stability. Summary of the Invention

[0003] In one aspect, the embodiments described herein relate to a method of forming a perovskite film, the method comprising: depositing ink onto a substrate, and annealing the substrate to form the perovskite film. The ink comprises: one or more 2D perovskite crystals; one or more group I cations or ammonium halides; one or more metal halides; and one or more solvents. The annealing may include heating the substrate to a temperature in the range of room temperature to 200°C.

[0004] The first group of cations or ammonium halides can be selected from the group consisting of formamidinium halides, cesium halides, guanidine halides, methylammonium halides, and combinations thereof. The metal halide can be lead iodide.

[0005] The ink may contain 0.1 to 50 mol% of the 2D perovskite crystals.

[0006] The 2D perovskite crystal may contain elements having the formula A'A n-1 B n X 3n+1 or A'An B n X 3n+1 The perovskite comprises a spacer cation A', where A is a monovalent cation, B is a divalent metal, n=1-7, and X is a halide. The spacer cation A' can be selected from the group consisting of butylammonium, pentylammonium, hexylammonium, heptylammonium, phenethylammonium, octylammonium, 4-aminomethylpiperidine, 3-aminomethylpiperidine, 3-(aminomethyl)pyridine, butanediamine, and combinations thereof.

[0007] The monovalent cation A can be selected from formamidinium, cesium (Cs), methylammonium, and guanidine. The halide X can be selected from the group consisting of iodides, bromides, chlorides, and combinations thereof. The divalent metal B can be lead, germanium, bismuth, copper, silver, gold, gallium, indium, antimony, tin, and combinations thereof. The 2D perovskite can be selected from the group consisting of BA₂PbI₄ and BA₂FAPb₂I₇. The perovskite film can contain materials selected from perovskites having the formula ABX₃, such as FAPbI₃.

[0008] The solvent may be a solvent having a Gutmann donor number greater than 10. The solvent may be selected from the group consisting of dimethylformamide, dimethyl sulfoxide, and combinations thereof. The solvent may be a mixture of DMF and DMSO, wherein the DMF:DMSO is provided in a ratio ranging from 1:1 to 9:1.

[0009] The method can also be used to form optoelectronic devices. These optoelectronic devices may include solar cells. The solar cells may exhibit an efficiency of at least 23.5%.

[0010] The embodiments disclosed herein also relate to a perovskite ink comprising: one or more 2D perovskite crystals; one or more group I cations or ammonium halides; one or more metal halides; and one or more solvents discussed above. Attached Figure Description

[0011] Specific embodiments of the disclosed technology will now be described in detail with reference to the accompanying drawings. Similar elements in the various drawings are indicated by similar reference numerals to maintain consistency.

[0012] Figure 1 This is a schematic diagram of a method for manufacturing a 3D stabilized perovskite film according to one or more embodiments.

[0013] Figure 2A In-situ absorption measurements are depicted during the evolution of α-FAPbI33D perovskite with excess n=1,2D RP during annealing, according to Example 1.

[0014] Figure 2BThe in-situ absorption measurements during the evolution of control FAPbI3 during annealing, according to Example 1, are depicted.

[0015] Figure 3 A comparison of grazing incidence X-ray diffraction (GIXRD) spectra of 2D stabilized FAPbI3 perovskite and control FAPbI3 is shown according to Example 1.

[0016] Figure 4 The relevant length and microstrain extracted from the Halder-Wagner plot according to Example 1 are shown as a function of the 2D perovskite concentration for stabilizing 3D FAPbI3 perovskite.

[0017] Figures 5A-5B The experimental logarithm of the WAXS diffraction pattern and its evolution over time during the formation of a 2D stabilized FAPbI3 thin film according to Example 1 are depicted.

[0018] Figure 6 The diagram shows a comparison of the degradation of control and 2D stabilized FAPbI3 extracted by integrating the main perovskite peak (001) as a function of time according to Example 1.

[0019] Figure 7 The shelf-life stability of the 2D stabilized FAPbI3 film, as measured by monitoring GIXRD under environmental conditions for 60 days according to Example 1, is shown.

[0020] Figure 8 The shelf-life stability of the 2D stabilized FAPbI3 film, as measured by monitoring absorption under environmental conditions over a period of 60 days according to Example 1, is shown.

[0021] Figure 9 The reported range of values ​​for the d(011) interplanar spacing and the FAPbI3d(001) interplanar spacing for n=1 and n=2 2D perovskites with various A′ cations (PA, BA, OA and PEA) according to Example 1 are shown.

[0022] Figure 10 This is a schematic diagram of the templated FAPbI3 drop coating method based on Example 2.

[0023] Figure 11 The integrated peak areas of (100)d (orange, left axis) and (001)3D (right axis) peaks are shown for control FAPbI3 (bottom), FAPbI3 with 0.5 mol% PEA n=2 added (middle), and FAPbI3 with 0.5 mol% BA n=2 added (top) over time according to Example 3.

[0024] Figure 12 The average azimuth integral wide-angle X-ray scattering (WAXS) pattern for each tested FAPbI3 additive (2D perovskite concentration of 1 mol%) according to Example 4 is shown within the first 90 seconds after annealing at 150 °C.

[0025] Figure 13 The a-FAPbI3(001) lattice parameters, measured at room temperature on individually prepared samples for films having 1 mol% of each 2D additive, according to Example 4, are shown.

[0026] Figure 14 A schematic diagram of the 2D templated FAPbI3 perovskite formation mechanism based on lattice matching is shown according to Example 4.

[0027] Figure 15A The diagram shows a representative azimuth-integrated nano-X-ray diffraction pattern obtained by integrating several nano-XRD patterns at different pixels within the test area for a BA2FAPb2I7-templated FAPbI3 film according to Example 5.

[0028] Figure 15B -C shows a representative azimuth integral nano-X-ray diffraction pattern for the BA2FAPb2I7-templated FAPbI3 film according to Example 5, after integrating several nano-XRD patterns obtained for different pixels in the test area for the (210) peak and (211) peak of BA2FAPb2I7-templated FAPbI3 respectively.

[0029] Figure 16 Histograms of the full width at half maximum (FWHM) values ​​of the nano-XRD peaks for different pixels of the BA2FAPb2I7-stabilized FAPbI3 film (left) and the MACl-stabilized FAPbI3 film (right) according to Example 5 are shown.

[0030] Figure 17 The absorption spectra of MACl-stabilized FAPbI3 (bottom line) and BA2FAPb2I7-stabilized FAPbI3 (top line) according to Example 5 are shown, with their band gaps indicated.

[0031] Figure 18 The photoluminescence (PL) spectra of MACl-stabilized FAPbI3 (bottom line) and BA2FAPb2I7-stabilized FAPbI3 (top line) according to Example 5 are shown.

[0032] Figure 19 The time-resolved photoluminescence (TRPL) spectra of MACl-stabilized FAPbI3 (bottom line) and BA2FAPb2I7-stabilized FAPbI3 (top line) according to Example 5 are shown.

[0033] Figure 20 The JV curves for the optimal device according to Example 6 are shown, which simultaneously show the forward scan (solid line) and the reverse scan (dashed line).

[0034] Figure 21 The external quantum efficiency (EQE) of the best 2D stabilized FAPbI3 device according to Example 6 is shown in comparison with that of the best MACl stabilized FAPbI3 device.

[0035] Figure 22 The stability test data of an unpackaged 2D FAPbI3 cell (top) and a MACl-FAPbI3 cell (bottom) using maximum power point tracking (MPPT) in ambient air at 60°C and under one day of sunlight, according to Example 6, are shown.

[0036] Figure 23 Stability test data for the packaged battery using MPPT at 60°C and under one day of sunlight, according to Example 6, are shown.

[0037] Figure 24 Stability test data for the packaged battery, based on Example 6, at 85°C under one day of sunlight, using maximum power point (MPP) tracking, are shown. Detailed Implementation

[0038] Specific embodiments of the invention will now be described in detail with reference to the accompanying drawings. Numerous specific details are set forth in the following detailed description of the embodiments to provide a more complete understanding of the invention. As used herein, "comprising" means "including but not limited to".

[0039] Typically, embodiments of this disclosure relate to a method of forming a perovskite material. The perovskite material may be in the form of a film coated on a surface comprising a conductive glass. The conductive glass may include a glass plate further coated with a transparent conductive material (such as indium tin oxide, indium oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide). The method may include depositing ink onto a substrate and annealing the substrate to form the perovskite material. The ink may comprise 2D perovskite crystals, one or more group I cations or ammonium halides, one or more metal halides, and one or more solvents. The ink provides a 2D perovskite crystal that can be used as a template to form a 3D bulk phase matching the 2D perovskite lattice.

[0040] An embodiment of the method is described in Figure 1 In the middle. For example Figure 1As shown, 2D perovskite seed crystals can be combined with inks comprising one or more Group I cations or ammonium halides and one or more metal halides or pseudohalides 101 (e.g., FAPbI3). The inks can be deposited onto a surface to form a film. The resulting film can be washed with a solvent or a combination of solvents (including diethyl ether) to aid crystallization 103 (so-called solvent annealing). During annealing, the deposited film may undergo an intermediate stage in which the color of the film changes according to its crystal structure, which will be explained in more detail in subsequent sections. Prior to solvent annealing 103, the film may contain 2D crystals and an undesirable 3D perovskite phase (e.g., hexagonal phase), as shown in the uncolored portion of 103. After further annealing (e.g., thermal annealing 105), the film contains cubic or near-cubic α-phase 3D perovskite material, such as FAPbI3 107.

[0041] The ink can also be referred to as a precursor solution. Although Figure 1 FAPbI3 is described as a precursor solution, but the method described herein is not limited to FAPbI3; therefore, other precursor solutions can be used to ultimately stabilize the resulting perovskite films. More specifically, as described above, the ink comprises one or more Group I cations or ammonium halides. Examples of Group I cations or ammonium halides include, but are not limited to, dimethylammonium halide, formamidinium (FA) halides, cesium halides, guanidine halides, and combinations thereof. As used throughout this disclosure, the term "halide" refers to halides and pseudohalides. Halides include fluorides, chlorides, bromides, and iodides. Pseudohalides include cyanides, cyanoacetylene oxides, isocyanides, hydroxides, hydrogen sulfides, hydrogen selenides, hydrogen tellurides, cyanates, isocyanates, fulminates, thiocyanates, isothiocyanates, selenide cyanates, telluride cyanates, azides, nitrogen oxides, tetracarbonyl cobaltates, trinitromethanes, tricyanomethanes, and gold compounds.

[0042] The ink further comprises one or more metal halides. The metal in the metal halide can be any suitable metal used in perovskites, and in some embodiments can be lead, germanium, bismuth, copper, silver, gold, gallium, indium, antimony, or tin. In one or more specific embodiments, the metal halide can be lead iodide. The halides are as described above.

[0043] The first group cation or ammonium halide and the metal halide can be combined in a ratio ranging from 1:1.1 to 1.1:1. The concentrations of the one or more first group cations or ammonium halides and the metal halide in the ink can range from 0.1 to 5 M, for example from the lower limit of any one of 0.1, 0.2, 0.5, 0.8, or 1.0 M to the upper limit of any one of 2, 3, 4, or 5 M, wherein any lower limit can be mathematically paired with any upper limit. As a non-limiting example, if FAPbI3 is a precursor in the precursor solution, it can have a concentration of 1.0 M in the solvent.

[0044] In one or more embodiments, the 2D perovskite seed crystals in the ink comprise crystals having the general formula A'A x B y X z (A'A) n-1 B n X 3n+1 The 2D perovskite comprises a bulky monovalent or divalent cation, A being a smaller monovalent cation relative to A', B being a divalent metal, X being a monovalent anion (such as a halide or pseudohalide), and n being the number of octahedrons in the quantum well, which may also be referred to as the layer thickness. Throughout this disclosure, it should be understood that stoichiometric variables describing the various components (e.g., "n" in the crystal structures listed in the above chemical formulas) do not necessarily correspond to precise integer values. As those skilled in the art will understand, the crystal system may include elemental substitutions, vacancies, and other defects. Therefore, it should be understood that references to integer values ​​such as n may include variations on the order of 0.1% to 10%. In one or more embodiments, the value of n ranges from 1 to 7 and may be 1, 2, 3, 4, 5, 6, or 7. In a particular embodiment, n is less than or equal to 4. In one or more embodiments, for a single n value, the phase-pure material is described by the above general formula. Suitable 2D perovskites can be halide perovskites, such as Ruddlesden-Popper 2D perovskite, Dion-Jacobson 2D perovskite, alternating cation 2D perovskites, and combinations thereof. The 2D perovskite crystals can be single crystals, possessing a crystalline structure and high phase purity (≥90%). For example, suitable 2D perovskites may include the compounds listed in Table 1 below.

[0045] Table 1

[0046] The ink may contain 0.1 to 20 mol% of 2D perovskite crystals, based on (B) the concentration of metal halide, for example from a lower limit of any one of 0.1, 0.5, 1, 5 or 10 mol% to an upper limit of any one of 12, 15, 17 or 20 mol%, wherein any lower limit may be mathematically paired with any upper limit.

[0047] According to one or more embodiments, the spacer cation A' (also referred to as the interlayer cation) can be any cation listed in Table 1, and in a particular embodiment it can be selected from the group consisting of butylammonium (BA), pentylammonium (PA), hexylammonium, heptylammonium, phenethylammonium (PEA), octylammonium (OA), 4-aminomethylpiperidine (4AMP), 3-aminomethylpiperidine (3AMP), 3-(aminomethyl)pyridine (3AMPY), butanediamine (BDA), and combinations thereof.

[0048] In the above chemical formula, the intralayer cation A can be any cation described in Table 1, and in specific embodiments may be selected from the group consisting of dimethylammonium, formamidinium (FA), cesium (Cs), guanidine (GA), and combinations thereof. Furthermore, X is a monovalent anion, such as a halide or pseudohalide as defined above. In specific embodiments, X may be selected from the group consisting of iodides, bromides, chlorides, and combinations thereof. B in the above chemical formula is a divalent metal, and in specific embodiments may be selected from the group consisting of lead, germanium, bismuth, copper, silver, gold, gallium, indium, antimony, or tin.

[0049] While any perovskite described in Table 1 can be used as a seed crystal, suitable 2D perovskite precursors include, but are not limited to, BA2PbI4 and BA2FAPb2I7 in certain embodiments.

[0050] The 2D perovskite crystals can be prepared using techniques known in the art. In short, a precursor (e.g., lead oxide, formamidine hydrochloride, and butylamine) is dissolved in an acidic solution (e.g., a mixture of hydrochloric acid and hypophosphoric acid), and stirred at an elevated temperature to dissolve the precursor. The solution is then cooled to room temperature, and 2D crystals ranging in size from micrometers to millimeters precipitate from the solution.

[0051] As described above, the ink may also contain a solvent. According to one or more embodiments, the solvent may be selected from the group consisting of DMF, DMSO, or mixtures thereof. For mixtures, the amounts of DMF and DMSO may be any suitable ratio of DMF:DMSO in the range of 1:1 to 9:1.

[0052] The inks described herein can be prepared by any suitable method known in the art. For example, the components described above can be combined and mixed with an appropriate amount of solvent (e.g., by stirring) until the components are dissolved / suspended in the solvent. Mild heating may be used as needed. The inks described herein may also be referred to as “seed solutions,” meaning solutions containing 2D seed crystals as described herein. As understood by those skilled in the art, inks are generally colored liquid materials used for writing and printing. In certain specific fields, inks comprise suspensions or dispersions of solid nanocrystals. The nanocrystals are stable, meaning they do not settle or precipitate from the solution within a reasonable timeframe (hours to days / weeks / months). In this disclosure, the nanocrystals are 2D perovskites. Therefore, the inks can be considered nanocrystalline inks. The inks can be used in printing applications, including spin coating, slot die coating, doctor blade coating, inkjet printing, and thermal evaporation (e.g., sublimation printing).

[0053] As described above, the methods described herein include depositing ink onto a substrate. According to one or more embodiments, the ink can be deposited using any suitable method, which may include spin coating, doctor blade coating, drop casting, and slot die coating techniques.

[0054] When perovskite materials are printed into film form (e.g., via the deposition steps described herein), annealing may be necessary to help fully crystallize the deposited film, thereby improving optical and electrical properties in applications such as photovoltaics (PV). Annealing can include thermal annealing by applying heat to above room temperature (typically above 25°C), solvent annealing by washing with one or more solvents, and photonic annealing by exposure to UV, visible light, and / or IR light sources.

[0055] Once a suitable amount of ink has been deposited onto the substrate, the substrate can be annealed to form a 3D perovskite film. The annealing can be performed at a suitable temperature for a suitable time to form the 3D film. The temperature can be in the range of room temperature to 200°C, such as from the lower limit of any one of 25, 30, 35, 45, 55, or 65°C to the upper limit of any one of 70, 80, 90, 120, 150, or 200°C, where any lower limit can be paired with any upper limit. The annealing time can be in the range of about 20 minutes to several hours, such as from the lower limit of any one of 20, 40, or 60 minutes to the upper limit of any one of 2, 3, 4, or 7 hours, where any lower limit can be paired with any upper limit. After annealing, a perovskite film can be formed. An exemplary perovskite film formed by the method described herein is a 3D FAPbI3 structure.

[0056] The exemplary FAPbI3 perovskite described above can be stabilized using a seed-based templating method with 2D n=1 Ruddlesden-Popper perovskite. As mentioned above, 2D n=1 or n=2 perovskites with different organic cations can stabilize formamidinium-based 3D perovskites. The lattice mismatch between the 2D and 3D perovskites can be used to minimize the 2D-3D interface energy and promote the growth of the 3D phase through templating. When a pure FAPbI3 precursor solution is contacted with the 2D perovskite, the black phase (α-FAPbI3) preferentially forms at 100°C, a temperature significantly lower than the standard FAPbI3 annealing temperature of 150°C. X-ray diffraction and optical spectroscopy indicate that the resulting FAPbI3 film is slightly compressed to obtain the (011) interplanar spacing of the 2D perovskite seed. Further details regarding the crystal growth mechanism are provided in the examples below.

[0057] In another aspect, the embodiments disclosed herein relate to a perovskite seed solution. The perovskite seed solution is as described above.

[0058] In another aspect, the embodiments disclosed herein also relate to a device comprising a perovskite film formed by the methods described above. The device includes a perovskite heterostructure comprising a substrate and a perovskite film on the substrate. The methods described above can be used to form a perovskite film for the device. Therefore, the perovskite film of the device can be formed from a precursor solution. As a non-limiting example, inks as described above can be used to form 3D stabilized perovskite films comprising FAPbI3 or other perovskites described herein.

[0059] In one or more embodiments, the perovskite heterostructure can exhibit properties desired for use in solar cells or other optoelectronic devices, including light-emitting diodes, radiation detectors, field-effect transistors, lasers, or any suitable device comprising a semiconductor. As described above, the methods disclosed herein can provide a stabilized 3D perovskite film with a low bandgap of approximately 1.48 eV. Therefore, the devices disclosed herein can comprise a perovskite film having an optimal bandgap for perovskite solar cells. In one or more embodiments, the solar cell device may include a substrate, an electron transport layer, a 3D perovskite film, a hole transport layer, and an indium tin oxide (ITO) layer.

[0060] According to one or more embodiments, the device may be a photoelectric device comprising a solar cell. For example, a perovskite solar cell comprising the disclosed solution-treated perovskite heterostructure can have an efficiency of 23.5% and provide a high open-circuit voltage (Vp) of 1.2 V in conventional nip devices (where n refers to the electron transport layer, i refers to the active material, and p refers to the hole transport layer). OC Furthermore, in perovskite solar cells incorporating the aforementioned exemplary perovskite heterostructure, high ISOS-L1 photostability can be observed when encapsulated. 99 Approximately 1000 hours. 99 This is related to the percentage efficiency of the solar cell retained after a certain number of durability test hours. In this paper, T... 99 The approximately 1000-hour timeframe describes how, under constant illumination using simulated sunlight, photovoltaic devices retain over 99% of their original efficiency after 1000 hours.

[0061] The thickness of the perovskite film can range from 1 nm to 1 μm. The device can have an interface transition of 1 to 30 nm between the substrate and the perovskite film. This process is compatible with other large-scale thin film processing techniques, such as blade coating, drop casting, and slot die coating.

[0062] Example General Procedures - Methods and Representations 1.1 Synthesis of High-Purity 2D Perovskite Powder The 2D Ruddlesden-Popper perovskite parent crystal BA2FAPb2I7 was synthesized by combining lead oxide (PbO, Sigma-Aldrich, 99%), formamidine hydrochloride (FACl, Sigma-Aldrich, ≥98%), and butylamine (BA, Sigma-Aldrich, 99.5%) in precise stoichiometric ratios. This mixture was dissolved in a solution of hydroiodic acid (HI, 57 wt% aqueous solution) and hypophosphorous acid (H3PO2, 50% aqueous solution) and stirred at 240 °C until the precursor materials were completely dissolved and the solution boiled. Subsequently, the precursor solution was cooled to room temperature, resulting in the crystallization of flat single crystals ranging in size from micrometers to millimeters. To ensure the quality and phase purity of the synthesized crystals, a comprehensive analysis was performed using a combination of X-ray diffraction and absorbance measurements.

[0063] 1.2 Gas-liquid interface method for BA2FAPb2I7 single crystal growth To synthesize large-area 2D Ruddlesden-Popper perovskite crystals BA2FAPb2I7, lead oxide (PbO, Sigma Aldrich, 99%), formamidine hydrochloride (FACl, Sigma Aldrich, ≥98%), and butylamine (BA, Sigma Aldrich, 99.5%) were combined in precise stoichiometric ratios. This mixture was dissolved in a solution of hydroiodic acid (HI, 57 wt% aqueous solution) and hypophosphorous acid (H3PO2, 50% aqueous solution) and stirred at 240 °C until the precursor materials were completely dissolved and the solution began to boil. The solution was then maintained at 100 °C without stirring. A clean glass was introduced into the bottom of a vial, allowing large-area crystals to form at the gas-liquid interface. After crystal formation, the glass was carefully removed from the vial with tweezers; the slightest movement facilitated retrieving the formed crystals. The resulting film on the glass was washed with diethyl ether and annealed at 125 °C to remove any trapped solvent from the crystals.

[0064] 1.3 Solar Cell Manufacturing Inverted planar perovskite solar cells: Patterned glass / ITO substrates were sequentially ultrasonicated for 15 minutes each in soapy water, deionized water, acetone, and a 1:1 mixture of acetone and ethanol. After drying the substrates and subjecting them to UV-ozone cleaning for 30 minutes, they were transferred to a glove box. Inside the glove box, a hole transport layer (HTL) with a thickness of approximately 10 nm was created using a SAM layer (MeO-2PACz, TCI, America) with a concentration of 0.8 mg / ml ethanol. The HTL was deposited by spin-coating at 5000 rpm for 30 seconds, followed by annealing at 100°C for 10 minutes.

[0065] To prepare a 1.0 M FAPbI3 perovskite precursor solution, PbI2 and FAI were mixed in a solvent mixture of DMF and DMSO (6:1). The solution was continuously stirred for 4 hours, followed by the introduction of various mol% formamidinium-based 2D perovskite A'2Fan+1PbnI3n+1, where A... ’ Different bulky organic cations, such as butylammonium and pentylammonium, were used and aged on a hot plate at 70°C for 30 minutes. A single-step spin-coating process was employed, with spin-coating at 5000 rpm for 30 seconds and an acceleration of 2500 rpm / s to achieve uniform coverage of the perovskite film. The samples were then annealed at 150°C for 20 minutes. Finally, the perovskite film was annealed at a temperature below 2 x 10⁻⁶. -6 The device was fabricated by vacuum thermal evaporation of C60 (30 nm), BCP (1 nm), and copper (100 nm). An effective area of ​​0.5 cm² was chosen for the device. 2 .

[0066] 1.4 Measurement of light absorption and photoluminescence Thin film absorbance measurement: Thin-film absorbance measurements were performed using the following setup: the sample was illuminated with modulated monochromatic light at a frequency of 2 kHz. The light was generated by a quartz-tungsten-halogen light source and passed through a monochromator (SpectraPro HRS 300, Princeton Instruments). To detect transmitted light, a silicon photodiode connected to an SR865 lock-in amplifier was used for synchronous detection. Measurements were performed in the spectral range of 400 to 800 nm, with a dwell time of 0.1 seconds at each data point. Throughout the experiment, the sample was held at approximately 10 nm. -4 It is kept under vacuum conditions and maintained at room temperature.

[0067] Steady-state photoluminescence (SS-PL) measurements were performed using a laboratory-built confocal microscopy system to obtain SS-PL data. Spectra were collected using an Andor Kymera 329i spectrometer and an Andor iDus 416CCD detector. The acquired spectra were then processed using Savitzky-Golay filtering to obtain the optimal signal-to-noise ratio. For photoexcitation, the sample was illuminated with a monochromatic pulsed laser with an emission wavelength of 2.58 eV (480 nm). The laser pulse duration was 6 ps, the repetition rate was 78.1 MHz, and focusing to near the diffraction limit achieved a resolution of approximately 0.5 µm. The excitation intensity was carefully adjusted to 360 W / cm². 2 PL measurements were performed in the spectral range of 450-900 nm with a residence time of 0.1 seconds. The experiment was conducted under vacuum conditions at room temperature (10... -5The procedure was performed under [unspecified] conditions. PL spectra were acquired by scanning a 40 µm × 40 µm or 100 µm × 100 µm region using a step size of 1 µm. At each step, the peak positions of the photoluminescence signal were extracted and recorded for further analysis.

[0068] 1.5 Time-Resolved Photoluminescence (TRPL) Measurement Time-resolved photoluminescence (TRPL) measurements were performed by exciting the sample with laser pulses of varying fluxes (420 nm, 40 fs pulse duration, 100 kHz repetition rate). These laser pulses were generated using a barium β-borate crystal by frequency doubling of laser pulses from a diode-pumped Yb:KGW femtosecond laser system (PHAROS). This laser pulse (beamspot size 20 µm) was then focused onto the sample using a lens with a focal length of 3.8 mm. Emitted light was collected from the transmission side using a Mitutoyo objective (numerical aperture = 0.7, magnification = 100×), followed by spatial filtering using a mechanical aperture located in the conjugate plane. Elastically scattered light was filtered out using a long-pass filter (wavelength 650 nm, optical density = 6.0). Furthermore, emitted light was filtered using a band-pass filter with a center wavelength of 800 nm (wavelength = 800 ± 20 nm, optical density = 4.0). The emitted light was then focused onto a Micro Photon Device (MPD) PDM series single-photon avalanche photodiode with an effective area of ​​50 µm. A time resolution of 64 ps was set in a bin size. The photoluminescence spectrum was collected by guiding the emitted light to a spectrometer using a flip-up mirror.

[0069] 1.6 Ultrafast transient absorption spectra Time-resolved absorption (TA) data of the sample were obtained using transient femtosecond pump-probe spectroscopy. The sample was excited using a 420 nm laser pulse generated by an optical parametric amplifier, with a pulse duration of 40 fs and a beam spot size of 120 µm. A diode-pumped Yb:KGW femtosecond laser system based on the chirped pulse amplification principle (PHAROS) generated light pulses with a center wavelength of 840 nm. These laser pulses were then passed through a 0.5 mm thick barium β-borate crystal, whose frequency was doubled to generate a 420 nm laser pulse, which was used as the pump pulse. These laser pulses were focused onto the sample, with a spot diameter of 120 µm (1 / e2). 2Another laser pulse from the amplifier is focused onto the sapphire crystal to generate a white-light supercontinuum that serves as the probe pulse. The optical path length between the pump and the probe is manipulated by passing the probe beam through a corner mirror mounted on a high-precision motorized translation stage. The probe pulse (35 µm in diameter) is then focused and spatially overlapped with the pump pulse onto the sample. It is then re-collimated and guided to a multimode fiber for wavelength-sensitive detection.

[0070] 1.7 X-ray diffraction measurement Using a Rigaku SmartLab X-ray diffractometer with Cu(Kα) radiation (λ=1.5406 Å), the diffractometer was used in the range of 2θ from 2° to 30°, with steps of 0.01° and 2 o 1D X-ray diffraction of 3D perovskite films was measured at a rate of [value missing] / minute. To determine lattice parameters, the film was scraped with a blade and rubbed onto a glass slide to remove any residual strain from the substrate. The scraped film was then coated with a thin layer of PMMA to prevent the α→δ transition during XRD measurements in air. Single-crystal X-ray diffraction of 2D perovskite crystals was obtained using a RigakuSynergy-S diffractometer with a Mo target. The temperature was maintained at 300 K.

[0071] 1.8 Differential Scanning Calorimetry (DSC) Measurement By spin-coating 300 µL of FAPbI3 precursor solution onto a large area (25 cm²) 2 On a substrate, FAPbI3 powder was prepared for DSC by vacuum drying at room temperature and scraping with a blade. DSC was performed using a TA DSC 250 at a scan rate of 1 °C / min.

[0072] 1.9 Nuclear Magnetic Resonance (NMR) Measurement By spin-coating 300 µL of FAPbI3 precursor solution onto a large area (25 cm²) 2 FAPbI3 powder for NMR was prepared by annealing and scraping with a blade on a substrate. The powder was dissolved in 600 µL of deuterated DMSO. Liquid-phase NMR was performed on a 600 MHz Bruker NEO digital NMR spectrometer. 1¹H NMR. A higher BA n=2 concentration of 5 mol% was used to better resolve the butylammonium signal. For solid-state NMR measurements, control 2D and 2D-doped FAPbI₃ films were deposited on glass substrates, scraped with a blade, and collected as powder. A higher 2D n=2 concentration of 10 mol% was used to better resolve the spacer cation signal. To minimize material degradation during solid-state NMR data collection, the materials were individually packed into hermetically sealed and opaque zirconia rotors (1.3 mm outer diameter) equipped with VESPEL caps. All in-situ solid-state MAS NMR experiments were performed at 21.1 T ( 1 The experiments were conducted at the Larmor frequency of H (900 MHz). The MAS frequency was 50 kHz in all SS NMR experiments. 1D values ​​were obtained by adding a total of 16 transients. 1 HMAS NMR spectroscopy. Based on saturation recovery measurements and analysis, an inter-scan delay of 45 seconds was set to ensure complete... T 1. Relaxation, thereby achieving quantitative proton peak intensity. 2D 1 H- 1 H-spin diffusion NMR experiments used a sequence similar to a three-pulse NOESY, with different mixing times for acquisition of the α-FAPbI3- low-dimensional phase (BA or PA). A rotor synchronization increment of 20 µs was applied to detect 400 [phases / phases]. t One increment, each increment having two co-addition transients. For all materials, 1 The H experimental displacement used adamantane as an external reference. 1 H resonance (1.81 ppm), calibrated relative to pure TMS.

[0073] From precursor compounds, control 2D materials, and 2D-doped FAPbI3 materials, 1D 1 In Hss NMR spectroscopy, it is possible to identify and distinguish ions corresponding to different organic cations. 1 H peak. For reference, FA was obtained. + of 1 The H signal (blue box) can be found in the BA-stabilized perovskite within the orange box. + The signal, shown in the purple box, represents PA in PA-stabilized perovskite. + Signal. By acquiring pure 2D BA2FAPb2I7 and PA2FAPb2I7 phases 1 Hss NMR spectroscopy further confirmed the origin of these signals. For FA... + and BA + Related 1 Comparison of H-peak integrals indicates that there is approximately 6 mol% of 2D phase in the 3D phase, and for the 2DPA2FAPb2I7 doped material, this amount is estimated to be approximately 7 mol.

[0074] To gain a deeper understanding of the local proximity relationship between BA and FA cations in the 2D BA2FAPb2I7 / PA2FAPb2I7-doped FAPbI3 phase, 2D... 1 H- 1 H-spin diffusion (SD) NMR experiments were performed and analyzed. Specifically, the magnetization exchange between dipole-coupled spins (in this case, protons) allows for the detection of spatial proximity relationships between adjacent sites, for example, the detection of spatial relationships between different organic cations. 1 H- 1 H. Proximity information. In 2D 1 H- 1 In H SD spectra, diagonal peaks provide information about chemical shifts, while off-diagonal peaks contain information about spin magnetization exchange between chemically inequivalent spins. For BA and PA-stabilized 3D phases, a mixing delay of 50 ms is insufficient to produce off-diagonal peaks, but a mixing delay of 500 ms results in BA peaks. + (orange), FA + (in blue) 1 Between H sites and BA + / FA + Between (green) and PA + / FA + The magnetization exchange between the two phases (gray areas) is shown in the green and gray boxes, respectively. These peaks indicate the coexistence of mixed 2D / 3D phases. The relatively strong intensity peaks observed for the BA-stabilized FAPbI3 phase indicate a higher degree of mixing of the 2D phase within the 3D phase compared to the PA-stabilized FAPbI3. Furthermore, the peaks within the purple and orange boxes indicate the close proximity of proton sites within the PA and BA cations, respectively.

[0075] 1.10 Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) Measurement High-resolution depth profiling was performed using a combined TOF-SIMS NCS instrument, which integrates a TOF-SIMS instrument (ION-TOF GmbH, Münster, Germany) and an in-situ scanning probe microscope (NanoScan, Switzerland). The instrument is located at Rice University's Shared Facilities Administration. The analytical field of view covers 80 × 80 μm. 2 area (Bi) 3 + (30 keV, 0.35 pA), with a raster scan of 128 × 128 during depth profiling. An electron neutralization gun was used throughout the analysis to compensate for charge effects. Charge effects were modulated using a surface potential of -36 V and an extraction bias of 0 V.

[0076] The cycle time was set to 90 μs, corresponding to a mass range of m / z = 0 – 735 amu. During sputtering, a 450 × 450 μm [size not specified] was used. 2 raster scanning (Cs) + @ 1 keV, 44 nA). The beam was operated in non-interlaced mode, alternating between one analysis cycle and one frame of sputtering (approximately 1.31 seconds), followed by a 2-second pause for charge compensation. MCs were also employed to enhance data interpretation. n+ (n = 1, 2) Depth profiling. This method is particularly useful for quantifying alloys and identifying ionic compounds. Cesium primary ion beam sputtering is used during depth profiling, enabling the detection of MCs. + or MCs 2+ Cluster ions, where M represents a combination of the target element and one or two Cs atoms. MCs are used in ToF-SIMS analysis. + and MCs 2+ Ions offer several advantages, including reduced matrix effects and the ability to detect compounds containing both electronegative and electronegative elements. All depth profiling was performed point-by-point normalized to total ionic intensity, and data were plotted using a 5-point adjacent averaging method. Normalization and smoothing techniques facilitated better comparison of data from different samples. Depth calibration was established by measuring thickness using a surface profilometer, which generates line scans of pits using in-situ SPM via contact scanning.

[0077] 1.11 In-situ WAXS measurements for FAPbI3 film formation The experimental setup was conducted in a custom-designed analytical chamber at the 12.3.2 microdiffraction beamline of an advanced light source. This dedicated chamber was designed to simultaneously accommodate various measurements and processes, including thin film handling. An indium tin oxide substrate, cleaned using plasma, was securely positioned on an integrated spin-coating chuck-heater and secured with thermal paste. To initiate the deposition process, a liquid precursor containing 1 MPb I₂ and formamidinium was carefully pipetted onto the substrate surface in a 6:1 DMF:DMSO solvent mixture. To maintain a controlled environment, the chamber was sealed from the external environment and kept under a continuous nitrogen flow. The experiment was conducted by subjecting the precursor to spin-coating, which consisted of two steps: a first spin-coating at 4000 rpm for 30 seconds to form a thin film. During the second spin-coating step, an ethyl acetate stream was dispensed precisely 10 seconds after the start of the process using a remote pipette. After the spin-coating was complete, a remote heating scheme was initiated. A nonlinear stepwise annealing sequence was applied, in which the substrate temperature was increased to 100°C in 20°C increments at 20-second intervals, and then increased to 150°C in 25°C increments. The temperature was then maintained at 150°C for the entire experimental duration (up to t = 300 seconds). The incident X-ray beam was guided at an incident angle of 1° and had a beam energy of 10 keV. The distance between the sample and the detector (referred to as the sample-detector distance (SDD)) was approximately 155 mm. The detector itself was positioned at a 39° angle relative to the sample plane. Wide-angle X-ray scattering (WAXS) data were acquired using a 2D Pilatus 1 M detector (Dectris Ltd.) with a 1.0-second exposure time and an additional 0.8-second pause between measurements (totaling 1.8 seconds). Photoluminescence excitation was achieved using a 532 nm Thorlabs diode-pumped solid-state laser with a power density of 40 mW / cm². The resulting photoluminescence signal was collected by a lens, guided into an optical fiber, and transmitted to a grating OceanOptics QE Pro spectrometer for detection. To adjust the annealing temperature and scheme, the temperature of the heating chuck was recorded using a pre-calibrated Raytek MI3 pyrometer. The temperature control system utilized a pre-programmed PID loop.

[0078] Calibration of Peak Position During Heating: It is known that the thermal paste holding the substrate expands with temperature, slightly altering the substrate height. This change in height also alters the sample-detector distance and the position of the direct beam relative to the detector, creating the illusion that the peak shifts to higher q values ​​as the temperature increases. Best practice is to correct for this height variation by maintaining the ITO peak at q = 2.15 Å⁻¹ during the temperature ramp. However, this peak overlaps with the (112) diffraction peak of the FAPbI₃ δ phase, which appears after antisolvent deposition and persists during the temperature ramp. Instead, we compared the position of the ITO peak at room temperature before antisolvent drop with its position at 150 °C after the δ phase transforms into the α phase. We hypothesize a linear relationship between temperature and substrate height variation, which allows us to use in-situ temperature data to correct for this peak shift during the temperature ramp.

[0079] 1.12 Dynamic Light Scattering (DLS) Measurement Experimental methods: Solutions of FAPbI3+BA2FAPb2I7 perovskite were prepared by dissolving the precursor and high-purity crystalline powder in DMF (as described in Section S1.3) and adding 5 mg and 10 mg of n=2 BA2FAPb2I7. The prepared solutions were placed in cylindrical glass cuvettes (Wilmad® NMR tubes, 5 mm diameter, high-throughput, 103 mm length). Dynamic light scattering (DLS) measurements were immediately performed by capturing correlation curves at four different angles (60°, 90°, 120°, and 150°). Measurements were performed using a fully automated 3D LS spectrometer (laser: 660 nm, 65 mW, LS Instruments AG, Fribourg) at an ambient temperature of 20°C. Each angle was measured three times. Extraction of particle size in solution: The following is a detailed description of the analysis of multi-angle dynamic light scattering (DLS) data obtained from precursor solutions of different concentrations. Autocorrelation curves were measured for each solution to examine its angle dependence. These correlation curves were then fitted using a single exponential decay model. The residuals from the correlation fitting were measured and plotted. Furthermore, a linear regression of Γ on q² was performed, focusing on the range between 60° and 150°. (Scattered light correlation function) g (2) The received signal strength was compared between time t and a later time t+τ. 5 )

[0080] Using the Siegert relation, which correlates the electric field correlation function with the intensity correlation function, it is given by the following equation: (6)

[0081] Where β is a constant proportional to the signal-to-noise ratio.

[0082] For a system undergoing Brownian motion, the electric field correlation function exhibits exponential decay, as shown below:

[0083] When there are several groups of different sizes (labeled as) in the solution i When fitting particles, the following formula can be used to fit DLS data: (6)

[0084] Then, for the particle group i , Γ i The value is obtained by relating the translational diffusion coefficient to the following formula. D T,i and wave number q Related:

[0085] in,

[0086] η is the refractive index of the solvent, λ is the wavelength of the laser beam, and θ is the angle between the incident laser beam and the scattered light. Finally, the diffusion coefficient is related to the hydrodynamic radius of the particle in Brownian motion using the Stokes-Einstein equation. R H Related: (7)

[0087] in k B It is Boltzmann's constant. T Temperature, μ is dynamic viscosity. R H,i It is a particle group i The median hydrodynamic radius.

[0088] 1.13 Nanometer X-ray diffraction measurement Nanoscale X-ray diffraction measurements were performed at a hard X-ray nanoprobe in the Advanced Photon Source 26 ID-C section at Argonne National Laboratory. Samples were fabricated on an X-ray transparent silicon nitride (Norcada, part number NX5050D) window for transmission geometry measurements, enabling near-normal incidence and minimizing beam projection onto the sample surface. Measurements were performed at an incident X-ray energy of 9.6 keV using an X-ray probe with a full width at half maximum (FWHM) of approximately 25 nm, focused using a Fresnel zone plate and an order-selective aperture to minimize the contribution of higher-order diffraction to probe broadening. Diffraction patterns were collected using a zero-noise diffraction CCD. The diffraction patterns were recorded using a Decris Eiger2 single-photon counting detector with a pixel width of 75 µm and angular resolutions of 0.018–0.023° per pixel at low and high doubling angles, respectively. Nanoscale diffraction patterns were generated using a dwell time of 0.1 sec per point. It was determined by measuring the X-ray diffraction patterns of all samples over time that the X-ray diffraction patterns remained consistent over many seconds of X-ray irradiation at a single point.

[0089] 1.14 Grazing Incidence Wide-Angle X-ray Scattering Experimental methods: The grazing incidence wide-angle X-ray scattering (GIWAXS) measurements presented in this paper were performed at two different synchrotron radiation beamlines: the 8-ID-E beamline of the Advanced Photon Source (APS) and the 11-BM beamline of the National Synchrotron Radiation Source II (NSLS II). For experiments conducted at the 8-ID-E beamline, the sample was positioned on a dedicated Linkam grazing incidence X-ray scattering (GIXS) stage placed inside a vacuum chamber at a pressure of 10 ppm. -4 A Pilatus 1M (Dectris) surface detector was positioned approximately 228 mm from the sample. A photon energy of 10.91 keV was used, and the X-ray beam size was 200 μm × 20 μm (horizontal × vertical). Experiments at the 11-BM beamline, on the other hand, employed a robotic stage positioned at 6 × 10⁻⁶ mm. -2 The sample was placed in a vacuum chamber under pressure. The distance from the sample to the detector was approximately 267 mm, and a Pilatus 800K (Dectris) surface detector was used. The photon energy used was 13.5 keV, and the X-ray beam size was 200 μm × 50 μm (horizontal × vertical).

[0090] In-situ GIWAXS during degradation is performed using a solvent vapor annealing chamber in an open sample loading area at 11-BM. The measurement beam enters and exits the chamber through Kapton windows on both sides. For high humidity measurements, liquid water is added to the bottom of the chamber to maintain the atmosphere at >90% RH. For light-based measurements, AM1.5G light enters the chamber through a glass window at the top. For heated measurements, a resistance heating element below the sample controls the chamber temperature.

[0091] GIWAXS analysis To analyze the GIWAXS pattern, full-angle integration was performed to obtain 1D X-ray spectra. The Debye-Scherrer equation was used to determine the average grain size (Dhkl) of the perovskite film, where (hkl) represents the Miller index. For the analysis of the 2D perovskite top film, the (200) crystal plane was used, while for the 3D perovskite film, the (001) crystal plane was chosen. The Scherrer equation includes a form factor (K) of 0.9. The formula is shown below:

[0092] in λ It is 1.1365 Å, which is the wavelength of X-rays. θ It is the position of the diffraction peak. β It is the full width at half maximum (FWHM). The FWHM is extracted by fitting the diffraction profile to a pseudo-Voigt function. The FWHM is then corrected for measurement geometry, such as X-ray beam divergence, energy bandwidth, and parallax effects of the beam spot.

[0093] 1.15 Thin Film Morphology Measurement Scanning electron microscopy (SEM) measurements: Surface and cross-sectional SEM images were acquired using a FEI Quanta 400 ESEM FEG instrument. The fabrication process involved depositing a 3D control and a 2D templated 3D perovskite film onto a silicon substrate, followed by sputtering approximately 15 nm of gold to improve film conductivity. SEM images were acquired at 12.5 kV with a dwell time of 30 μs during image acquisition.

[0094] Atomic force microscopy (AFM) measurements: AFM measurements were performed using a Park Systems NX20 AFM instrument. Surface topography images were acquired in tapping mode using a silicon probe with a resonant frequency of 300 kHz and an elastic constant of 26 N / m. Root mean square (RMS) roughness values ​​were extracted from the 5 μm × 5 μm images.

[0095] 1.16 Determination of electronic energy levels using photoelectron yield spectroscopy (PES) PES (AC-2, Richen-Keiki) measurements were performed to determine the valence band maximum (VBM) of 3D and 2D (BA2FAPb2I7) templated 3D perovskite samples. Measurements were conducted under ambient conditions, with the samples irradiated with monochromatic ultraviolet (UV) light. The energy level of the UV photons used exceeded the ionization energy (IE) of the sample being measured. These photons ionized electrons to the vacuum level, which in turn ionized gas molecules near the surface, as detected by the instrument. During the measurements, the photon energy ranged from 4.2 eV to 6.2 eV, and the number of photoelectrons generated at each energy level was recorded. This recorded value was corrected based on the spectrum of the UV lamp used. For semiconductors, the number of photoelectrons near the VBM typically increases with the cube root of the energy. Therefore, the cube root of the corrected PYSA spectrum was plotted against the photon energy. A linear region above the starting point was fitted to determine the VBM, which was identified at the intersection of the linear fit and the background level. To calculate the conduction band minimum (CBM) relative to the vacuum level, the measured band gap is subtracted from the ionization energy to obtain the electron affinity (EA).

[0096] 1.17 Characterization of Solar Cell Devices Solar cell performance: The performance of the solar cells was obtained by measuring the current-voltage (JV) curves of each device under illumination using an ABB solar simulator (model 94011) at Newport. The arc simulator simulated AM 1.5G irradiance of 100 mW / cm². 2 The intensity was calibrated using a NIST-certified silicon solar cell (Newport 91150V, ISO 17025) and corrected for by measuring the spectral mismatch between the solar spectrum, the reference cell, and the spectral response of the PV device. We estimated the mismatch factor to be 3%. The solar cell was measured using a Keithley 2401 instrument after 10 seconds of light immersion, within a voltage range of 1.2 V to 0 V and a return voltage, with a step size of 0.05 V and a dwell time of 0.1 seconds. The defined effective area was 3.14 mm². 2 .

[0097] External quantum efficiency: The external quantum efficiency (EQE) of the solar cell devices was collected by first illuminating each device with monochromatic light modulated at 2 kHz from a quartz-tungsten-halogen light source fed into a monochromator (SpectraPro HRS300, Princeton Instruments). The photocurrent response of the solar cells was measured using an SR865 lock-in amplifier. The spectral response of the light source was calibrated using a calibrated silicon diode (FDS1010, Thorlabs).

[0098] Stability test:For stability testing, the perovskite devices were encapsulated in an argon-filled glove box using UV-curable epoxy resin (Poland Inc.) and a glass cover glass as a barrier layer. Just before encapsulation, the devices were purged with an argon gun to remove any contaminants or dust particles. All devices were tested at continuous maximum power point conditions in air at full-spectrum simulated AM 1.5G (100 mA cm⁻¹). -2 The test was conducted using an ABB solar simulator (94011A, Newport) under irradiance conditions—ISOS-L1 protocol. Data points were collected at 15-minute intervals. The relative humidity was kept constant at 60 ± 5% RH. H .

[0099] 1.18 Formation Mechanism of 3D FAPbI3 In our synthetic method, selective 2D perovskite crystals (BA2FAPb2I7) were dispersed in a FAPbI3 solution containing FAI:PbI2 (1:1) dissolved in DMF:DMSO solvent. Subsequently, we observed submicron-sized crystallites, termed 2D seed crystals, which maintained their perovskite structure and acted as nucleation sites during film formation. (42) Following spin coating, these 2D crystals transfer their n-values ​​to a solution-processed film comprising both 2D perovskite (BA2FAPb2I7) and the δ-phase of FAPbI3. During annealing, we propose a transformation to the bulk FAPbI3 phase via an intercalation process. + Pb 2+ and I - Plasma infiltrates the lattice from the edges of the 2D-HaP crystal and diffuses along the interfaces between perovskite layers. These ions fill the voids in the PbI6 structure, forming additional connections and interacting with [Pb]. n I 3n+1 Lattice integration to form a 3D bulk FAPbI3 pushes large organic cations to the grain boundaries. The observed templating effect is attributed to the fine ionic interactions between the 2D inorganic octahedral sheets and the organic spacer groups, and the lattice matching between the 2D perovskite (BA2FAPb2I7) and the 3D FAPbI3 crystal faces. Our results are consistent with previous reports of precursor ion intercalation into the lattice to form higher-thickness 2D-HaP. (45) .

[0100] Example 1 This example demonstrates the methylammonium-free and cesium-free stabilization of formamidinium perovskite for high-efficiency stable devices. To elucidate the mechanism of perovskite film formation, the inventors conducted… In situ Absorbance, photoluminescence, and wide-angle X-ray scattering (WAXS) measurements were performed simultaneously with spin coating and annealing for 5 minutes at any temperature between 100 and 150 °C.

[0101] This example involves using a two-dimensional Ruddlesden-Popper (n=1) perovskite as a starting template to stabilize a three-dimensional (3D) FAPbI3 perovskite. Stabilization of the 3D FAPbI3 perovskite utilizes a 2D n=1 or n=2 Ruddlesden-Popper (RP) perovskite with an organic spacer cation. Suitable organic spacer cations include one or more of butylammonium, pentylammonium, phenethylammonium, and octylammonium. A 2D n=1, 2, or 3 perovskite (e.g., BA2PbI4 or BA2FAPb2I7) is introduced as an excess additive into an equimolar solution of formamidinium iodide (FAI) and lead iodide (PbI2) used to prepare the 3D HaP FAPbI3 film. Film formation follows an intermediate 2D perovskite stage, which acts as a template or seed crystal for preparing the stabilized cubic (α) phase FAPbI3.

[0102] FAPbI3 perovskite was successfully stabilized using a seed-based template method with 2D n=1 Ruddlesden-Popper perovskite. 2D n=1 or n=2 perovskites with different organic cations (such as butylammonium, pentylammonium, octylammonium, and phenethylammonium) have been shown to stabilize formamidinium-based 3D perovskites. The film quality of the 3D FAPbI3 layer was not compromised, exhibiting high crystallinity compared to control FAPbI3 films or multi-cation stabilized FAPbI3 perovskite films. An optimal band gap of approximately 1.48 eV was achieved, which is the optimal band gap for α-FAPbI3 perovskites and lower than that of FAPbI3 typically stabilized at A cation sites. Accelerated aging conditions (85 °C, 85 R) were also observed. H High material stability was measured under continuous illumination (AM1.5G and X-rays). The inventors fabricated a solar cell with an efficiency of 24.1%, which, in a conventional NIP device structure, J SC 26.5mA.cm -2 Open circuit voltage (V) OC The voltage was 1.14 V with a fill factor of 80%. The versatility of this technology was tested using 2D RP n=1 and n=2 perovskites with different organic cations (e.g., pentylammonium, octylammonium, and phenylethylamine). High ISOS-L1 photostability was observed in the operating solar cells, and the TV of the encapsulated devices was [not specified]. 99 >1000 hours, T of unpackaged device 90 >500 hours indicates the high stability of photovoltaic devices under operating conditions.

[0103] The designed strategy was tested for Dion Jacobson phases (e.g., (3AMP-PbI4)), which preferentially form 2D HaP perovskite and then stabilize 3D FAPbI3 perovskite, taking into account strong interlayer interactions. The resulting FAPbI3 film exhibited a bandgap of 1.48 eV, which is the optimal bandgap for the α-FAPbI3 phase. We further fabricated nip and pin solar cells with a maximum PCE of 23.5%, achieved at 26.0 mA·cm⁻¹. -2 High current density, 82% fill factor, and 1.14 V open-circuit voltage (V OC The fabricated device was achieved under accelerated testing conditions (85 R). H It exhibits enhanced material stability under 85°C and continuous AM 1.5G illumination, and also provides T for epoxy-encapsulated devices. 99 Device stability >1000 hours, with T for unpackaged devices. 90 Device stability >500 hours.

[0104] Figure 1 A schematic diagram is shown depicting a strategy for stabilizing FAPbI3 perovskite using Ruddlesden-Popper n=1 or n=2 2D perovskite. Figure 2A and 2B The schematic diagram illustrates the various stages involved in obtaining stabilized FAPbI33D perovskite. Stabilized FAPbI33D perovskite may be free of one or more of methylammonium, cesium, rubidium, and bromine. The process involves adding trace amounts of 2D or RP (n=1 or n=2) perovskite from the ink as an excess additive to an equimolar concentration of FAI and PbI2 dissolved in a solvent mixture of dimethylformamide and dimethyl sulfoxide. This synthesis technique shows an intermediate phase (red film) that eventually transforms into a black α-FAPbI3 phase at 100°C or 150°C. This contrasts with typical synthesis methods, where a yellow δ-FAPbI3 phase initially forms after spin coating, which transforms into α-FAPbI3 upon annealing at 150°C.

[0105] Figure 2A and 2B The absorbance evolution of 3D FAPbI3 films during continuous ramp annealing (0 to 150 °C) using two techniques was depicted. Figure 2A The annealing process is shown. In situ Absorption measurements depict the evolution of α-FAPbI33D perovskites with excess n=1 or n=22D RP. Figure 2A The comparison with FAPbI3 is shown. In situ Absorption measurement results. Normal synthesis method ( Figure 2BThis demonstrates the direct transformation from δ-FAPbI3 to α-FAPbI3 during annealing, while using our method ( Figure 2A We observed the intermediate BA2FAPb2I72D RP phase, which eventually transforms into α-FAPbI3 upon annealing. As previously reported, the control ( Figure 2B ) and 2D stabilized FAPbI3 ( Figure 2A The absorption band edge and blue shift of photoluminescence of 2D stabilized FAPbI3 are purely temperature-dependent. Furthermore, compared to control FAPbI3, 2D stabilized FAPbI3 (… Figure 2A The film exhibits a weak Urbach tail absorption, indicating high electronic quality.

[0106] The figure shown In situ PL measurements show similar transformation behavior and characteristics. The results during annealing are shown. Original Bit Photoluminescence measurements depict the evolution of α-FAPbI3 3D perovskites with excess n=1 or n=2 2D RP. An inset shows the PL evolution of the control FAPbI3.

[0107] The crystal structure during film formation was monitored using synchrotron radiation WAXS technology. In situ The changes were observed, and the evolution of the α-FAPbI3 3D perovskite structure during stabilization using 2D n=1 or n=2 RP perovskites was demonstrated. The formation of a yellow δ-FAPbI3 phase immediately after spin-coating was observed, which transforms into 2D BA2FAPb2I7, via q < 1 Å. -1 The orientation Bragg spot at the location was identified, and the spot eventually disappeared and transformed into α-FAPbI3, which was verified by concentric diffraction rings.

[0108] The crystallinity of the final perovskite films obtained by the two methods was investigated using grazing incidence X-ray diffraction (GIXRD). Figure 4 ). Figure 4 The GIWAXS spectra of 2D stabilized α-FAPbI3 perovskite (red line) and control FAPbI3 (dashed black line) are shown for comparison. In 2D stabilized α-FAPbI3, at a diffraction angle of (2θ, CuKα) 14.1... o and 28.2 o Two main diffraction peaks corresponding to the (100) and (200) crystal planes were observed at the point, while the normal synthesis method showed multiple peaks corresponding to the hexagonal (δ phase) and cubic (α phase) phases of FAPbI3 perovskite.

[0109] Halder-Wagner plots were generated to extract the coherence length and microstrain in different samples with varying concentrations of 2D RP n=1 or n=2 perovskite additives. The plot shows the coherence length and microstrain extracted from the Halder-Wagner plots as a function of the 2D perovskite concentration used to stabilize 3D FAPbI3 perovskite. At a concentration of 1.0 wt%, the coherence length increased from 22.62 nm to 38.4 nm, while for a concentration of 2.0 wt%, it further decreased to 33.97 nm. The decrease in microstrain validated the relaxation of local lattice strain with the introduction of 2D RP n=1 or n=2 perovskite. This result indicates that 2D stabilized FAPbI3 exhibits higher crystallinity, reduced atomic defects, and nonradiative recombination compared to the control sample.

[0110] Optical absorption and photoluminescence spectra of 2D stabilized FAPbI3. The absorption (black line) of the 600 nm stabilized FAPbI3 film and the photoluminescence spectrum for excitation at 1.96 eV (red line) are shown. The optical band gap (E0) was measured to be 1.48 ± 0.002 eV. g This optical band gap is the optimal band gap for α-FAPbI3, which is lower than that of most A cation-stabilized FAPbI3 reported in the literature.

[0111] The material stability of control FAPbI3 and the material stability of FAPbI3 stabilized by our method were investigated. A method was developed... In situ The intrinsic stability of the device stack (ITO / SnO2 / FAPbI3 / Sprio-MeOTAD / Au) was tested using a GIWAXS aging system at 85°C and 85°R. H The structural degradation of perovskite was monitored under accelerated aging conditions of continuous AM1.5 G illumination and open-circuit voltage.

[0112] Contour plots depicting the integral peak intensity changes of various diffraction peaks of FAPbI3 fabricated using two different technologies were analyzed. The contour plots show the degradation of control FAPbI3 over time, as well as the degradation of a stack of 2D perovskite-stabilized FAPbI3 thin-film devices (unencapsulated) over time. The control FAPbI3 showed immediate degradation to δ-FAPbI3 and PbI2, with its intensity continuously increasing over time at the expense of the α-FAPbI3 phase intensity. After 35 minutes, most of the control α-FAPbI3 transformed into the δ phase, with PbI2 present. However, as... Figure 5A and 5BAs shown, the experimental logarithm of the WAXS diffraction pattern of FAPbI3 stabilized using our method during film formation and its evolution over time exhibit extremely high stability throughout the 3-hour period, with almost no degradation of the main perovskite (001) peak.

[0113] Figure 6 The graph shows a comparison of the degradation of control and 2D stabilized FAPbI3 extracted by integrating the main perovskite peak (001) as a function of time. Figure 6 The high intrinsic material stability of 2D stabilized FAPbI3 is demonstrated. Figure 7 The integral peak intensity of the main perovskite peak (001) in the device stack (control and 2D stabilized FAPbI3) extracted from in-situ degradation measurements is shown as a function of time. Figure 8 As shown, in an ambient atmosphere (humidity of 55%)... H After 1440 hours in 2D stabilized FAPbI3, no macroscopic traces of δ-FAPbI3 phase formation were observed.

[0114] Specifically, Figures 7 to 8 Macroscopic traces of the absence of the δ-FAPbI3 phase were shown in 2D stabilized FAPbI3, as measured by GIXRD. Figure 7 ) and absorption measurement ( Figure 8 This has been confirmed. Figure 7 The shelf-life stability of 2D stabilized FAPbI3 films, measured by monitoring GIXRD under ambient conditions over a period of 60 days, is shown. Figure 8 The shelf-life stability of the 2D stabilized FAPbI3 film, measured by monitoring absorption under ambient conditions over a 60-day period, is shown. We observed only some PbI2 formation as degradation after 1440 hours. All these measurements demonstrate that stabilized FAPbI3 provides a durable stabilizing effect on phase impurities for both bare devices and films operating or measured under stringent external stress sources.

[0115] The band arrangement of the photoactive phase of FAPbI3 stabilized using 2D, n=1 RP perovskite was obtained by combining photoelectron yield spectroscopy with band gap (assessed from Tauc plots) and compared with that of MACl-stabilized FAPbI3 to verify the feasibility of fabricating solar cell devices. The arrangement of FAPbI3 with appropriate transport layers and electrodes for fabricating nip geometry shows the energy level arrangement of nip solar cell stacks with different FAPbI3 photoactive absorbers fabricated by 2D perovskite stabilization and MACl stabilization. This demonstrates that the optimal 2D stabilized FAPbI3 n-ip perovskite solar cell is a suitable device.

[0116] An appropriate band alignment for charge carrier (electron or hole) extraction was observed. The current-voltage curves and external quantum efficiency (EQE) of the optimally stabilized 2D FAPbI3n-ip perovskite solar cell demonstrate the stacked absorption and current generation capabilities. The current density measured from the current-voltage curves matches very well with the integral current density calculated from the EQE.

[0117] Following ISOS-L-1 guidelines, operating at a temperature of 55°C and a temperature range of 50-60°R. H The long-term operational stability of 2D stabilized FAPbI3 packaged devices under ambient humidity conditions is demonstrated, showing the ISOS-L-1 stability of epoxy-encapsulated PSCs measured under ambient conditions, after one continuous day of sunlight exposure (55°C) and maximum power point tracking. After 1000 hours of continuous illumination, the FAPbI3 stabilized devices showed negligible degradation. 99 >1000 hours. The solar cell achieved a maximum PCE of 23.5%.

[0118] Considering the high intrinsic material stability, we also measured the unencapsulated FAPbI3 solar cells under continuous illumination, at an operating temperature of 55°C, and at 50-60 R. H At % ambient humidity. The ISOS-L-1 stability of the unpackaged PSC, measured under ambient conditions, continuous one day of sunlight exposure (55°C), and maximum power point tracking, is shown. After 500 hours, the stabilized FAPbI3 device exhibits T... 90 >500 hours, while the control FAPbI3 device degraded by more than 80% before 50 hours of continuous illumination.

[0119] Example 1 illustrates that embodiments of this disclosure can provide at least one of the following advantages: An optimal bandgap of 1.48 eV is achieved, enabling the fabrication of high-efficiency nip and pin solar cells with a maximum PCE of 23.5%. At 85°C and 85°R... H Accelerated stability tests conducted under % and continuous light immersion revealed extremely high material stability and excellent device stability. Furthermore, high ISOS-L1 light stability was observed in the operating solar cells, and the To of the encapsulated device was also observed. 99 >1000 hours, T of unpackaged device 90 >500 hours indicates the high stability of photovoltaic devices under operating conditions.

[0120] Example 2 This example illustrates the overall design principles, lattice matching analysis based on 2D perovskite-templated FAPbI3, and proof of concept. Figure 9The average in-plane lattice parameters corresponding to the Pb-I-Pb distance, i.e., the (011) plane of 2D perovskite and the (001) plane of 3DFAPbI3 perovskite, are shown as a function of the layer thickness or n value of 2D perovskite formed by a series of A' site cations (PA, BA, OA, and PEA). The red solid lines represent the average lattice parameters of the strainless phase FAPbI3 obtained from previous reports on its single-crystal structure. The reported range of lattice parameter values ​​for the d(001) plane spacing of FAPbI3 is plotted as gray horizontal bars. A'2FAn-1PbnI3n+1 RP 2D perovskite, where A' = BA, PA, PEA, or OA. For BA2FAPb2I7 and PA2FAPb2I7, the (011) spacing is close to the (001) spacing of the metastable and strainless phase FAPbI3. Following the lattice mismatch model developed for MAPbI3, 42 Assuming low lattice mismatch between 2D and 3D perovskites to minimize 2D-3D interface energy and promote growth through templated methods, this has inspired a search for FA-based 2D perovskites with in-plane lattice parameters close to those of FAPbI3. FA-based n=2 2D perovskites with bulky cations butylammonium (BA) and pentylammonium (PA) were found, with (011) interplanar spacings of 6.359 Å and 6.368 Å, respectively, which are almost perfectly lattice-matched with the (001) interplanar spacing of 3D FAPbI3 (6.359 Å, averaged from two reported lattice constants of 6.352 Å and 6.365 Å) (lattice mismatches of 0% and 0.15%, respectively). 5,6 The lattice matching of FA-based perovskites with bulky cation butylammonium (BA) was further evaluated in the crystal structures of α-FAPbI3 and BA2FAPb2I72D perovskites, with a focus on the projections of the (001) and (011) crystal planes. A typical BA2FAPb2I72D perovskite structure is shown in two crystal orientations, displaying the projections of the (111), (011), and (200) crystal planes. Furthermore, the figure highlights the lattice-matching planes in the 3D and 2D perovskites, corresponding to the Pb-I-Pb distance and their lattice parameters, respectively.

[0121] On the other hand, crystal structure analysis reveals that for FA-based n=2 2D perovskites with phenylethylammonium (PEA) and octylammonium (OA), the Pb-I-Pb distances are smaller (6.261 Å and 6.336 Å, respectively), and produce larger lattice mismatches with the 3D unstrained structure (1.54% and 0.36%, respectively). Notably, all n=1 2D perovskites exhibit lattice mismatches with their 3D counterparts, indicating that they are unsuitable for templated 3D phases. Due to the intrinsic structural instability of unstrained FAPbI3, a stable strained FAPbI3 black phase is formed instead through a templated effect observed between the (001) plane of FAPbI3 and the (111) plane of the 2D perovskite. Therefore, the (111) interplanar spacing of the 2D n=2 structure is also shown in Figure 9 In China, guided by design principles, a drop-casting experiment for 2D perovskite lattice templating of FAPbI3 was developed.

[0122] like Figure 10 As shown, a FAPbI3 precursor solution was dropped onto a glass substrate and allowed to flow over BA2FAPb2I7 crystals. Upon heating, the d-FAPbI3 on ​​top of the BA2FAPb2I7 crystals transformed into α-FAPbI3 before the d-FAPbI3 on ​​top of the bare substrate. When placed in ambient air, the α-FAPbI3 on ​​top of the bare substrate transformed into d-FAPbI3 before the α-FAPbI3 on ​​top of the BA2FAPb2I7 crystals. Initially, a red millimeter-scale BA2FAPb2I7 single-crystal film was fabricated using a gas-liquid interface method and spread onto an ITO glass substrate, partially covering the substrate. Once these crystals were dried on a hot plate at 100°C, half of the glass slide was wiped away to produce a bare glass area covering approximately 50% of a 1-inch glass area. A few drops of FAPbI3 precursor solution (composed of equimolar amounts of FAI and PbI2) were added to a blank surface, and the substrate was annealed at 100°C, 125°C, and 150°C. Figure 10 The experiment shown was conducted at a substrate temperature of 100°C. After annealing, the solution was allowed to flow onto and react with the BA2FAPb2I72D perovskite crystal film. Upon contact with the 2D crystal, the solution spontaneously (within 10–15 seconds) transformed to form a shiny black film. The same results were obtained at 125°C and 150°C, all showing the same transformation. After equilibrating the film for 5 minutes, three distinct regions were obtained on the substrate, as shown... Figure 10 As shown: i: BA2FAPb2I7 without FAPbI3 solution, ii: BA2FAPb2I7 below FAPbI3 solution, and iii: FAPbI3 solution on bare glass.

[0123] The lower region of the substrate, initially bare glass, turned black at 100°C, exhibiting partially transformed α-FAPbI3. The middle region of the solution-contacted 2D perovskite consisted of the black FAPbI3 phase on the surface and BA2FAPb2I7 beneath it. Finally, in the upper part of the substrate, the area where the solvent did not flow remained a BA2FAPb2I7 crystalline film. The film was left to stand under ambient conditions for one hour. As the temperature decreased, the bottom region transformed into the yellow phase of FAPbI3, while the middle region remained black, indicating successful phase stabilization of FAPbI3. Due to its intrinsic stability compared to its 3D counterpart, the BA2FAPb2I7 crystalline film remained unchanged during this time period.

[0124] The final film was characterized using photoluminescence (PL) and X-ray diffraction (XRD) measurements in three regions. PL spectra of the film were obtained in three specific regions (labeled (i), (ii), and (iii)). The red region (i) is the BA2FAPb2I7 single crystal region not exposed to the FAPbI3 solution. The black region (ii) is the edge of the BA2FAPb2I7 single crystal in contact with the FAPbI3 solution. The yellow region (… Figure 10 Region (iii) corresponds to the relative edges of the sample, where the FAPbI3 sample is on glass. PL spectra of two different regions, one (region 1) at the top of the 2D crystal and the other (region 2) where the 2D crystal is absent.

[0125] Region (i) shows dominant PL emission at 2.15 eV, corresponding to the exciton ground-state emission of the BA2FAPb2I7 film, accompanied by a small shoulder peak near 2.0 eV. The intermediate region (ii) shows strong emission peaking at 1.48 eV, corresponding to the intrinsic bandgap of the α-FAPbI3 phase, with very weak emission near 2.15 eV, consistent with PL emission measured on the BA2FAPb2I7 single crystal. These results indicate the coexistence of a bulk black-phase FAPbI3 3D perovskite with a 2D perovskite crystal top. The extent of complete conversion to the BA2FAPb2I7 depth is limited by the low amount of FA precursor used in this experiment. The presence of the bottom 2D perovskite was confirmed by photoluminescence measurements taken from the back side of the film in region (ii), showing emission solely from the 2D perovskite. As expected, region (iii) remains devoid of any emission due to the photoinactive nature of the yellow phase of FAPbI3.

[0126] Furthermore, the integral PL peak as a function of probe intensity shows exciton peaks (blue and red, respectively) for n=2 and the hypothetical (n=3) peaks. The log-log linear fitting constant is k=0.9 when measured at 2.15 eV and k=1.2 when measured at 1.95 eV. Phase stabilization of FAPbI3 also occurs at 100 °C and 125 °C, temperatures well below the standard annealing temperature of 150–160 °C.

[0127] X-ray diffraction measurements verified that Figure 10 Findings from measurements in the middle regions. Diffraction results from region (i) show pure 2DBA2FAPb2I7 perovskite, evidenced by strong out-of-plane (h00) diffraction planes originating from the inorganic layer stack. A similar diffraction pattern was found from region (ii), but with (001) and (002) diffraction planes from the FAPbI3 phase perovskite, indicating a mixture of 2D and 3D perovskites. Finally, in region (iii), XRD showed only the presence of the yellow (δ) phase FAPbI3.

[0128] The above results indicate that incorporating BA2FAPb2I7 into FAPbI3 during film formation can stabilize the perovskite phase by templating the interatomic distances between the two structures, Pb-I-Pb.

[0129] Example 3 To verify the hypothesis of FAPbI3 film formation, 2D perovskite was added as a template agent to a precursor solution of 1:1 FAI:PbI2 in a 4:1 DMF:DMSO mixed solvent. Using a technique previously developed in our lab, pre-synthesized 2D crystals were added instead of the more conventionally chosen A' cation halide salt. Instead of completely dissolving into constituent ions in the DMF:DMSO solvent, the 2D crystals decompose into submicron-sized crystallites that retain their perovskite structure and act as nucleation sites during film formation. These 2D crystals can transfer their initial n-value to the solution-processed film. However, when dissolved in a FAPbI3 precursor solution (rather than pure DMF:DMSO), the 2D perovskite crystallites are surrounded by a high concentration of mobile A-site cations, which tend to intercalate into the seed crystals and increase their n-value. Therefore, a 2D dopant with a given A' site cation will grow from the FAPbI3 solution in such an environment with its thermodynamically preferred n-value. With this in mind, only 2D perovskites with n values ​​precipitated from FAPbI3 solution can be considered as template candidates. Solution processing experiments revealed that all RP 2D perovskites considered in this paper were grown from their n=2 phase in FAPbI3 solution.

[0130] Differential scanning calorimetry (DSC) was used to perform differential scanning calorimetry on the FAPbI3 films scraped before annealing, comparing the results with and without 2 mol% BA n=2 dopant (red) versus no dopant (black). The results showed that 2D-doped FAPbI3 underwent a δ→α transition at a lower temperature. 1D XRD data were also collected for spin-coated FAPbI3 solutions doped with 10 mol% A' iodide salt and annealed at 70 °C for 5 min, targeting BAI, PAI, OAI, and PEAI. In each case, A'I precipitated as phase-pure A'2FAPb2I7. This confirms that dopant BA2FAPb2I7 and PA2FAPb2I7 are physically feasible candidates for FAPbI3 templating. We found that, for the same molar concentration, there is no qualitatively different behavior between the FAPbI3 film doped with BA2PbI4 (n=1) and the film doped with BA2FAPb2I7 (n=2). Therefore, crystals of any n value can be used as a source of 2D seeds.

[0131] Doping with selected 2D perovskites BA2FAPb2I7 and PA2FAPb2I7 enables the fabrication of stabilized FAPbI3 perovskite films. For example... Figure 1 The film formation process of FAPbI3 with 2D perovskite additives provides insight into the changes that occur during this process. Perovskite films were synthesized by spin coating using a precursor with a FAI:PbI2:2D perovskite molar ratio of 1:1:x mol%. After antisolvent washing with diethyl ether, the films underwent a series of intermediate stages, visually manifested as color changes: from pale red (before annealing) to dark brown, finally turning black upon annealing at 100°C to 150°C for 20 minutes.

[0132] To elucidate the mechanism of RT-phase stable FAPbI3 film formation, we used synchrotron-based in-situ wide-angle X-ray scattering (WAXS) to measure the structural dynamics of perovskite during film formation. Perovskite films were deposited from solution onto ITO substrates in a WAXS chamber under nitrogen atmosphere using a robotic antisolvent pipette and a self-heating spin coater. We first investigated the crystallization dynamics of FAPbI3 films doped with 1.0 mol% BA₂FAPb₂I₇. WAXS patterns captured during film formation show concentric diffraction rings corresponding to Bragg reflections of the stacked axial diffraction planes of BA₂FAPb₂I₇ and the α and δ phases of 3D-FAPbI₇. The corresponding temporal evolution of the diffraction patterns during film formation (presented in the WAXS patterns captured during film formation) shows the coexistence of δ-FAPbI₃, α-FAPbI₃, and BA₂FAPb₂I₇ diffraction peaks.

[0133] The structural evolution of the film during in-situ spin-coating of a 1 mol% BA n=2 FAPbI3 precursor solution was observed by integrating the WAXS pattern with the azimuth angle and plotting it over time, spin-coating speed, and temperature. The in-situ experiment consisted of four steps: i) antisolvent dripping during spin-coating, ii) spin-coating followed by but before annealing, iii) slow ramp-up from room temperature to 150 °C, and iv) isothermal annealing at 150 °C. The δ-phase FAPbI3 formed immediately after antisolvent deposition (10 seconds, stage (i)), characterized by strong (100)... δ (q (length of the reciprocal lattice vector) = 0.84 Å) -1 ),、(101) δ and (110) δ Diffraction plane indication. Once spin coating is complete (30 seconds), the persistent δ phase, acting as a 2D BA2FAPb2I7 seed crystal, begins to crystallize at room temperature from the 2D out-of-plane (40°). 2D (q = 0.646Å) -1 ) and (600) 2D (q = 0.960Å -1 The diffraction peaks prove this.

[0134] As the substrate temperature increases, the diffraction peak intensity of BA2FAPb2I7 increases until δ-FAPbI3 begins to transform into α-FAPbI3, after which the peak slowly weakens. The position of the BA2FAPb2I7 (400) peak changes over time from below the expected value (tensile strain) and relaxes to the expected (400) peak position of BA2FAPb2I7 single crystal diffraction.

[0135] Next, a nonlinear stepwise annealing sequence was applied, in which the substrate temperature was increased to 100°C in steps of 20°C at 20-second intervals, and then increased to 150°C in steps of 25°C (stage iii). The slow heating to 150°C allowed observation of the onset temperature of the FAPbI3α phase peak. At this stage, results showed that the diffraction intensity of 2D increased significantly when annealed at low temperatures (<100°C), and at q = 1 Å. -1A new peak appears at the (001) plane of the α phase FAPbI3. The α phase exhibits very slight tensile strain (about 0.1%) at the beginning of its formation, but undergoes lattice compression during annealing, from 6.36 Å at the (000) plane to 6.275 Å at the (111) plane (about 1.4% compressive strain). Interestingly, the strain lattice parameter of 6.275 Å does not correspond to the (011) interplanar spacing (2D Pb-I-Pb distance) of BA2FAPb2I7, but rather to the (111) interplanar spacing. In fact, the 1.4% compressive strain is significantly higher than that of FAPbI3 templated on (011) BA2FAPb2I7 (which has almost no compressive strain). Concurrent with the appearance and growth of the α phase peak, a decrease in the δ phase peak and compression of the δ phase (201) and (220) interplanar spacings were observed.

[0136] Furthermore, such as Figure 11 As shown, it was observed that for FAPbI3 doped with 0.5 mol% BA n=2, (100) δ and (001) 3D The integral peak area is a function of time. (001) 3D The peak appears after 75 seconds and slowly intensifies as the (100)d peak decreases simultaneously. At approximately 130–150 °C, the remaining δ phase abruptly transforms into the α phase. As the film continues to anneal at 150 °C for the remainder of the experiment (stage iv), the 2D diffraction peaks slowly weaken, and the residual traces of the 2D perovskite are eventually eliminated (approximately 200 seconds), leaving only the slowly growing and stronger α phase FAPbI3.

[0137] Example 4 The formation of the stabilized film was repeated for a variety of other precursor solutions, including: i) undoped FAPbI3 without additives, ii) FAPbI3 stabilized with 35 mol% MACl phase, iii) concentration-dependent doped BA2FAPb2I7 crystals, and iv) 2D perovskite crystals doped with various other families.

[0138] The 1:1 FAI:PbI2 solution was evaluated in the in-situ contour WAXS plot of undoped FAPbI3. The behavior of the FAPbI3-2D sample (which showed a gradual emergence of the α phase between 100 and 150 °C, followed by a complete δ→α transition at approximately 130–150 °C) contrasted with the additive-free control FAPbI3, which exhibited a more abrupt transition from the δ phase to the α phase near approximately 150 °C. In the control FAPbI3, the (001)3D peak appeared later with a shorter tail, and the (100)d peak did not decrease prematurely as in the BA-doped n=2 film. Although the initial appearance of the α phase with the 2D dopant occurred at a much lower temperature, the complete δ→α transition in the 2D-doped sample was delayed compared to the control sample, suggesting that the presence of BA2FAPb2I7 slowed the FAPbI3 crystallization kinetics, even if it lowered the energy barrier for α phase growth. The additive-free control FAPbI3 exhibited a pre-strained α phase with a Pb-I-Pb distance of 6.32 Å (consistent with previous work). During annealing, the control lattice was further compressed from 6.32 Å to 6.30 Å, with a relative strain of -0.32%. Unlike the film with added BA n=2, the (001)3D peak of the control FAPbI3 did not become stronger with continued annealing at 150 °C.

[0139] The experiments were repeated for a 1:1:35 mol% FAI:PbI2:MACl precursor solution in a 4:1 DMF:DMSO mixture. Introducing MA into the A sites of FAPbI3 reduced the effective tolerance factor and stabilized the α phase at a lower temperature compared to undoped / additive-free FAPbI3. As a result, a sudden α→δ transition occurred at approximately 75 °C for the FAPbI3-MACl sample. However, as with the control sample and in contrast to the 2D-doped sample, no gradual δ→α transition region was observed, again indicating a lack of templating effect. The α-phase Pb-I-Pb distance of the FAPbI3-MACl film initially was 6.32 Å, then rapidly decreased to 6.29 Å, subsequently slowly expanding back to 6.32 Å with sample annealing. This expansion indicates the gradual volatilization of the MA cations and Cl atoms (unstable above 100 °C) and the resulting increase in the effective A site radius.

[0140] Next, BA₂FAPb₂I₇ (n=2) was added to a 1:1 PbI₂:FAI mixture at concentrations of 0.25, 0.5, and 1.0 mol%. In all cases, contour plots from in-situ WAXS experiments showed an increased intensity of the (001) 3D peak relative to the control. The formation behavior appeared to be concentration-independent. In all cases, 2D seed crystals formed prior to annealing, the α phase appeared at low temperatures, and the δ→α transition was slowed. Furthermore, the same α(001) plane compression of approximately 6.36 Å → 6.27 Å was observed in all films. In all cases, the results indicate that even trace amounts of BA n=2 can improve the crystallinity of the α phase, as they all exhibited (001) 3D The increase in peak size. FAPbI3 doped with 0.5 mol% BA n=2 showed a similar film formation process to the 1.0 mol% sample, i.e., at a lower temperature (100°C). δ Peak reduction and (001) 3D The peaks appeared slowly. However, compared to the control, the addition of 0.25 mol% BA n=2 did not lower the onset temperature of the (001)3D peak, nor did it cause the same characteristic decrease in intensity below 150 °C for the (100)d peak. Phase stabilization appeared to be concentration-independent until a certain minimum 2D concentration below which the template effect was lost, but the film crystallinity still improved. Furthermore, the 2D (400) peak indicated that all three concentrations had the same out-of-plane lattice parameters, initially shrinking (approximately 19.5 Å) before annealing and expanding towards a strain-free lattice (19.7 Å) with increasing temperature.

[0141] A series of 2D additives, including PA n=2, OA n=2, and PEA n=2, were then examined. The effect of PA n=2 was evaluated using in-situ WAXS measurements. Contour and parametric plots of PA n=2 doped in FAPbI3 at a weight percentage of 1.0 mol% showed a similar effect to BA n=2, namely, lowering the onset temperature of the α-phase peak and causing a reduction in the d-phase below 150 °C. In contrast, contour and parametric WAXS plots revealed significantly different effects for OA n=2 and PEA n=2. For FAPbI3 films based on OA n=2 at a weight percentage of 0.1 mol%, the 2D peaks formed weakly, and the α-phase appeared earlier than in the control sample, but no d→a transition was observed. Conversely, the d-phase persisted throughout the annealing process, indicating that OA2FAPb2I7 seeds can act as nucleation sites for FAPbI3 to a limited extent, but slow down the d→a transition. FAPbI3 doped with 0.5 mol% PEA (n=2) did not show a 2D peak or early α phase. Furthermore, FAPbI3 doped with 1 mol% PEA (n=2) retained the d-phase peak throughout the measurement process, indicating that PEA2FAPb2I7 not only failed to form seeds for templated FAPbI3 but also suppressed the d→a transformation kinetics. Neither OA2FAPb2I7 nor PEA2FAPb2I7 doped samples showed α-phase lattice shrinkage; instead, they retained the Pb-I-Pb spacing of the control sample, suggesting that neither dopant could template the α-phase FAPbI3.

[0142] Figure 12 A summary of the average azimuth integral WAXS pattern of the FAPbI3 sample with 1 mol% 2D BA and PEA during the first 90 seconds of annealing at 150 °C is shown. Additional graphs reveal that the film doped with 1 mol% OA and PEA n=2 exhibits an incomplete δ→α transition, in contrast to the complete transition of the film doped with 1 mol% BA and PA n=2. Notably, all 2D films showed a slow decrease in 2D peak intensity and a slow increase in (001)3D peak intensity during annealing at 150 °C, which was not observed in the control films. While the gradual volatilization of the A′ cation in A′2FAPb2I7 (leaving FAPbI3) could explain these changes, optical and nuclear magnetic resonance (NMR) results suggest that the 2D phase was not completely lost due to volatilization, and a competing mechanism for 2D reconstruction may exist within the lattice.

[0143] In-situ WAXS results showed that BA2FAPb2I7 and PA2FAPb2I7 could template the α-phase FAPbI3, but OA2FAPb2I7 and PEA2FAPb2I7 could not. Ex-situ 1D XRD was performed on individual 1 mol% 2D-doped FAPbI3 films. Ex-situ 1D XRD showed that FAPbI3 films with OA n=2 or PEA n=2 had the same (001)3D interplanar spacing (approximately 6.365 Å) as the control FAPbI3, but PA n=2 and BA n=2 caused small but significant compression of the (001)3D interplanar spacing, at -0.03% and -0.07%, respectively. Since the (011)2D interplanar spacing of BA n=2 is slightly smaller than that of PA n=2, FAPbI3 with BA n=2 has a higher compressive strain compared to that with PA n=2, which also supports the (011) lattice template hypothesis.

[0144] To verify the structural results, similar in-situ spectroscopic measurements were performed on BA2FAPb2I7-templated FAPbI3 samples. In the initial stages of annealing, the film exhibited a strong exciton absorption peak at 2.15 eV corresponding to BA2FAPb2I7, which transitioned to α-FAPbI3 as annealing progressed, characterized by a 3D perovskite absorption band edge. Similarly, in in-situ PL measurements, strong emission of the BA2FAPb2I7 perovskite was observed at 2.15 eV, accompanied by broad emission at lower energies. Butylammonium showed a wider bandgap distribution and required a longer time (200 s) to transition to the FAPbI3 bandgap. The lower-energy emission is presumably due to a combination of effects, including edge-state emission (46, 47), the formation of a higher n-value 2D phase (e.g., n=3BA2FA2Pb3I10) (48, 49), and quantum confinement effects of 2D and FAPbI3 microcrystals (50–53). Subbandgap edge-state emission in BA2FAPb2I7 was verified by spatially resolved photoluminescence (PL), showing a PL emission peak of 1.8 eV only at the edge of the stripped BA2FAPb2I7 single crystal. Furthermore, the presence of a PL emission peak at 1.85 eV and the observation of n=3 excitons in the power-dependent PL indicate that FA intercalation increases the layer thickness from n=2 to n=3 during annealing, ultimately forming 3D FAPbI3. Similar broad emission below the n=2 bandgap was observed during film formation of FAPbI3 with PA2FAPb2I7 additives, consistent with the structural results of PA2FAPb2I7. However, no subbandgap emission was observed for control FAPbI3 or FAPbI3 doped with MACl, OA2FAPb2I7, or PEA2-FAPb2I7.

[0145] Based on in-situ WAXS and PL measurements, we propose the following film formation process mediated by 2D templated annealing. The film first forms d-phase FAPbI3 grains and 2D seed crystals under RT. 2D is likely to form initially due to its more negative formation enthalpy, its RT phase stability, and the presence of 2D (approximately 3 μm) seed crystals in the precursor solution, as confirmed by dynamic light scattering (DLS) measurements. The grain size was determined by comparing 2 mol% and 4 mol% BA n=2 doped FAPbI3 using DLS. The correlation function (g2) versus retardation time at multiple scattering angles was measured, and the corresponding fits were superimposed to determine the grain size. During annealing, the d-phase remodels from the low-energy surface of the 2D seed crystals to form the α-phase FAPbI3. At the interface with FAPbI3, the arrangement of PbI6 octahedra in the 2D perovskite likely promotes the nucleation of the stable α-phase FAPbI3, subsequently undergoing a phase transition to the bulk phase (54). The inferred growth mechanism favors the formation of the compressive strain α-phase (001) plane, templated by the 2D (011) crystal plane spacing, such as... Figure 13 As shown. The error bars represent the standard deviation based on data from three to five samples. Low-temperature α-phase formation was observed only in films with added PA and BA n=2, and these films were also the only ones exhibiting lattice strain, which is strong evidence for the (011)2D spacing template effect.

[0146] The (011) interplanar spacing of BA2FAPb2I7 (6.359 Å) and PA2FAPb2I7 (6.364 Å) is almost perfectly lattically matched with the (001) 3D interplanar spacing of FAPbI3, both falling within the reported FAPbI3 lattice constant range of 6.352 to 6.365 Å (5, 6), while the (011) interplanar spacing of OA2FAPb2I7 (6.336 Å) and PEA2FAPb2I7 (6.265 Å) is poorly matched. This structural difference explains why OA-2D and PEA-2D do not exhibit the same d→a transformation process as BA-2D and PA-2D. The templating process and the resulting FAPbI3 strain appear to be independent of 2D concentration until a minimum threshold, which is between 0.25 and 0.5 mol% for BA-2D perovskites. When the temperature was raised to 150°C and the sample continued to anneal, we speculate that the 2D perovskite simultaneously volatilized its A' cation and underwent a slow FA intercalation process, which increased its n value.

[0147] Other reports indicate that the A' cations in 2D perovskites incorporated into FAPbI3 completely volatilize during annealing, except for a small fraction remaining at the grain boundaries (19, 38, 39). This explains the disappearance of our 2D signal over time and the slow increase in the intensity of the (001) 3D peak during annealing at 150 °C. Solid-state 1H NMR on scraped FAPbI3 films was evaluated. NMR of FAPbI3-5 mol% BA2PbI4 films annealed at different temperatures (70 °C for 3 min, 150 °C for 20 min, and 200 °C for 20 min), after scraping with a blade and dissolving the resulting powder in deuterated DMSO before and after annealing, did reveal partial volatilization of the spacer cations during film formation, but also confirmed that a considerable proportion of BA and PA remained even after annealing at 150 °C for 20 min. After annealing at 200 °C for 20 min, almost all BA had left the film. The distribution of time-of-flight secondary ion mass spectrometry (ToF-SIMS) as a function of depth (nm) and at cation concentrations of 0 mol%, 0.5 mol%, and 1.0 mol% was investigated. TOF-SIMS results showed that the remaining 2D spacer cations were uniformly distributed up to 1 mol%, while at higher concentrations, the distribution was more pronounced at the membrane-substrate interface.

[0148] BA and PA cations lead to the formation of a mixed 2D-3D phase, which is difficult to characterize using the aforementioned long-range techniques. Instead, high-field (21 T) solid-state NMR spectroscopy was applied to resolve the local structure of the organic cations in the mixed phase. The 1H NMR peaks associated with the large (BA and PA) and small (FA) cations were well resolved, thus allowing identification and quantification of the amount of the 2D phase present in the templated FAPbI3 material. Furthermore, analysis of the local structure of the mixed phase elucidated by the 2D 1H-1H correlated NMR spectra revealed spatial intermolecular interactions between the large cations (BA or PA) in the 2D phase and the small cations (FA) in the 3D FAPbI3 phase. Based on these findings, a comprehensive schematic diagram was formed to capture the different stages of film formation in 2D templated FAPbI3. Figure 14 ).

[0149] Example 5 It is hypothesized that the observed compressive lattice strain imposed by the templated 2D phase could lead to the formation of locally segregated tetragonal phase structures (55, 56). To investigate the effect of 2D stabilization on the nanoscale structural properties of FAPbI3, nanoscale XRD was performed on MACl-stabilized FAPbI3 and 2D-stabilized FAPbI3 using an X-ray probe with a 25 nm spot size. The high brightness of the synchrotron radiation source enabled the resolution of diffraction from the secondary phase (57, 58). The Pearson correlation coefficient of the CCD image of the diffraction pattern relative to the initial diffraction CCD image was measured over a 10-second irradiation time. The significant correlation over a long period indicates that the X-ray stability is much longer than the 100 ms dwell time used for nanoprobe diffraction patterning. Both films showed sufficient X-ray stability to accommodate the measurements. Localized X-ray scattering from the cubic phase (i.e., the α phase) and the tetragonal phase was observed. Representative summation diffraction charge-coupled device images from the 2D-stabilized FAPbI3 pattern were collected. Figure 15A As shown, azimuth integral nano-XRD patterns were collected for BA2FAPb2I7-templated FAPbI3 films. In addition to strong scattering from the cubic perovskite lattice, two subtle peaks at 1.57 Å, belonging to the tetragonal phase, were also observed. (210)t (t = tetragonal phase) at 1 and 1.866 Å (211)t at position 1 Figure 15B-15C Since there are overlapping (210)h (h = hexagonal phase, d phase) peaks at almost the same scattering vector, the (211)t peak cannot be definitively attributed to the tetragonal phase, but the (210)t peak is clearly identified (59). Furthermore, since no additional scattering peaks from the hexagonal phase were observed in this sample, the (211)t peak was attributed to the tetragonal phase. The diffraction intensity from the tetragonal phase is much lower than that from the cubic phase, and the total summation diffraction intensity of the (211)t peak is 0.8% of the intensity of the (200)c (c = cubic phase) peak.

[0150] To investigate the effect of 2D stabilization on the quality of perovskite crystallites in the thin film, 5D rocking curves (rocking curves using a 2D detector and 2D spatial mapping) were performed on the samples, where the incident X-ray angle varied, and the spatial map in the sample plane was repeated in the same region to accurately analyze the diffraction peak width.

[0151] 2D stabilized FAPbI3 exhibits a significantly narrower full width at half maximum (FWHM) diffraction peak than MACl-doped FAPbI3. Figure 16Narrower diffraction peaks may be due to increased domain size or reduced microstructural disorder (microstrain) (60). However, the strong evidence of increased domain size observed when MACl is included in the perovskite precursor suggests that the smaller domain size in MACl-doped FAPbI3 is not the cause (26, 61, 62). The conclusion is that 2D stabilization leads to a reduction in structural disorder within the film crystallites, consistent with previous reports (54). Halder-Wagner analysis of microstrain and coherence length in BA2FAPb2I7 crystals with different concentrations further reveals that the microstrain in 2D-stabilized FAPbI3 decreases with increasing 2D concentration. The following concentrations were investigated: 35 mol% MACl, 0.25 mol% BA n=2, 0.5 mol% BA n=2, and 1.0 mol% BA n=2. The strain ε and crystallite size D were extracted from the XRD data using Halder-Wagner plots, as shown in the following equations: , in

[0152] It is the integral width of the reciprocal lattice point.

[0153] is the reciprocal lattice plane spacing, and K is the shape factor.

[0154] Grazing-incidence WAXS (GIWAXS) patterns of MACl-doped FAPbI3 perovskite films were collected, and FAPbI3 with BA2FAPb2I7 additives revealed two distinct properties of the films. The MACl-doped FAPbI3 films exhibit Bragg intensities extending along an arc segment, indicating random orientation of crystalline domains or grains within the polycrystalline film (high mosaicism). Furthermore, these films exhibit PbI2 diffraction peaks. In contrast, the 2D-stabilized FAPbI3 films show well-defined Bragg diffraction points along the (001) plane at q = 1 Å. Observations were made on the Debye-Scherrer rings near 1. This unique observation indicates a smaller mosaicism and improved grain orientation in the out-of-plane direction perpendicular to the substrate. Furthermore, the mosaicism appears to decrease with increasing 2D concentration. Atomic force microscopy also showed that the FAPbI3 grain size increased as the 2D concentration increased from 0.25 mol% to 0.5 mol%, although a further increase to 1.0 mol% resulted in a decrease in grain size. These results are consistent with observations of improved crystallinity in FAPbI3 films even with the addition of small amounts of BA n=2.

[0155] Compared to MACl-doped FAPbI3, an increase in absorption was observed in 2D-stabilized FAPbI3. For tricationic Cs... 0.05 FA 0.85 MA 0.10 Pb(I 0.9 Br 0.1 )3, derive the band gap of 1.61 eV. For example... Figure 17 As shown, for the MACl-doped film, a band gap of 1.53 eV was derived, which is closer to the reported minimum band gap of FAPbI3 (1.48 eV) (5). Furthermore, the band gap value was evaluated using Shockley-Queisser limiting curves, comparing it to the optimal value of 1.34 eV. This band gap reduction is consistent with experimental characteristics of decreasing lattice disorder (54). In the polymorphism picture of the cubic phase of FAPbI3, the reduction in polymorphism also leads to a decrease in the tilt amplitude (4, 63). With increasing 2D concentration, the valence band maximum decreases, and the band gap widens. For MACl-doped FAPbI3, the VBM is 5.34 eV. For 0.25 mol% BA n=2, the VBM is 5.15 eV. For 0.50 mol% BA n=2, the VBM is 5.23 eV. For 1.0 mol% BA n=2, the VBM is 5.26 eV.

[0156] We also observed that the PL intensity of 2D stabilized FAPbI3 increased by an order of magnitude compared to MACl-doped FAPbI3, indicating a reduction in nonradiative recombination. Figure 18 The PL peak positions of both membranes are aligned with the absorption threshold. In time-resolved PL measurements ( Figure 19 Compared to the reference, the 2D stabilized FAPbI3 film exhibited a slower PL decay rate, indicating a reduction in nonradiative recombination attributed to trap-mediated bulk or surface recombination processes.

[0157] Example 6 Perovskite solar cells were fabricated using an inverted structure with 2D-stabilized FAPbI3, employing MeO-2PACz{[2-(3,6-dimethoxy-9H-carbazole-9-yl)ethyl]phosphonic acid} as the hole transport layer and C60 as the electron transport layer. To construct the band structure, we measured the valence band maximum and conduction band minimum of both MACl-doped FAPbI3 and 2D-stabilized FAPbI3 by combining photoelectron yield spectroscopy (PES) and absorption measurements. While slightly shifted to higher energies compared to MACl-doped FAPbI3, the 2D-stabilized FAPbI3 exhibits an appropriate band alignment for charge carrier separation and extraction.

[0158] The current density-voltage (JV) characteristics of the optimal performance 2D stabilized FAPbI3 device under reverse and forward bias sweeps are shown in the figure. Figure 20 Under AM1.5G illumination, for an effective area of ​​0.5 cm², a PCE of 24.1% was measured, and the short-circuit current density (JSC) was 25.5 mA·cm². 2. The open-circuit voltage (VOC) is 1.12 V, and the fill factor (FF) is 82%. These parameters are comparable to the corresponding thermodynamic limits (31.1 mA·cm⁻¹). It has an advantage compared to 2, 1.21 V and 89% (64). Figure 21 The external quantum efficiency (EQE) of the device with the same JV curve is shown. To confirm the effect of concentration on performance, solar cells were fabricated under the same conditions using different 2D perovskite concentrations. The statistical distributions of JSC, VOC, FF, and PCE for 40 devices under each condition were evaluated. The JSC obtained by integrating the EQE over wavelength is 24.3 mA·cm⁻¹. 2. This is in excellent agreement with the device JV curve measured using a solar simulator. For comparison, FAPbI3 devices stabilized with 0.5 mol% PA2FAPb2I7, OA2FAPb2I7, and PEA2FAPb2I7 were fabricated. The PA-templated FAPbI3 devices showed a PCE of 21% and JV. SC 25.2 mA·cm 2, V OC The voltage was 1.06 V, and the FF was 78.1%. For the optimized OA and PEA templated FAPbI3, a PCE of 16.54% (J) was achieved. SC It is 23.93 mA·cm 2, V OC (0.97 V, FF 71%) and 14.65% PCE (J SC It is 23.15 mA·cm 2, V OC (V is 0.96, FF is 65%).

[0159] Finally, we compared the intrinsic and operational stability of undoped, BA₂FAPb₂I₇-templated, and MACl-doped FAPbI₃ films and devices. Compared to undoped and MACl-doped FAPbI₃, 2D-templated FAPbI₃ was highly stable under various conditions. The shelf-life stability of the 2D-stabilized FAPbI₃ film showed a significant improvement over the 0-30 day timeframe compared to undoped FAPbI₃. Furthermore, we compared pristine undoped FAPbI₃ with 0.5 mol% NA n=2-doped film samples in ambient air for 10 hours. At 0 hours, the 0.5 mol% BA n=2-doped FAPbI₃ sample showed a strong peak, indicating the α-FAPbI₃ phase and very little δ-FAPbI₃, while the 10-hour ambient air sample almost entirely produced the δ-FAPbI₃ phase. We also compared the color changes between undoped and 0.5 mol% BA n=2-doped FAPbI₃ films. Undoped FAPbI3 films degraded within 10 hours, while 0.5 mol% BA n=2-doped FAPbI3 films showed almost no degradation over 30 days. In-situ GIWAXS measurements were also performed to compare the stability of MACl-doped and BA2FAPb2I7-doped FAPbI3 devices under >90% RH, 65°C, and one day of sunlight exposure. The 2D-templated FAPbI3 device exhibited minimal a→d transition within 170 minutes under the degradation environment. In contrast, the d phase became dominant in the MACl-doped FAPbI3 device within the first 15 minutes of measurement. The significantly higher stability of the 2D-templated FAPbI3 device in this experiment confirms... Figure 22 The stability test of MPPT devices with 2D templated FAPbI3 and MACl-doped FAPbI3 is shown.

[0160] We evaluated the stability of devices with standard interfaces. First, measurements were performed on unencapsulated pin solar cells using MPPT under ambient air and one day of sunlight (without a UV filter). Figure 22 As shown, the 2D templated device exhibited almost no PCE decline during the first 500 hours of operation, with T99 > 500 hours. In contrast, the unencapsulated MACl-doped FAPbI3 sample degraded during the first 50 hours of operation, showing T40 = 50 hours. Furthermore, as... Figure 23As shown, the packaged 2D templated FAPbI3 device exhibits almost no efficiency degradation from an initial 21% PCE after ambient air, MPPT, and continuous sunlight exposure for over 1000 hours (T99 > 1000 hours) (ISOS-L-1 scheme). This stability is among the best reported for FAPbI3-based perovskite devices, and in recent reports (26, 27, 36), these devices were measured under inert conditions. Furthermore, as... Figure 24 As shown, the encapsulated solar cells (ISOS-L-2 scheme) were measured in ambient atmosphere, on a hot plate at 85°C, MPPT, and under one day of sunlight. The 2D stabilized FAPbI3 device retained 99% of its initial PCE after 620 hours and over 97% of its initial PCE after 1000 hours. Using the rule of thumb from silicon photovoltaics, a 10°C increase in temperature corresponds to a 2-fold increase in degradation rate (64), T97 = 1000 hours at 85°C corresponds to T97 = 16000 hours (1.8 years) at 45°C. This result is a key step towards FAPbI3-based devices with commercially relevant stability.

[0161] Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily understand that many modifications can be made to the exemplary embodiments without substantially departing from the invention. Therefore, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

1. A method for forming a perovskite film, the method comprising: The ink is deposited onto the substrate, the ink comprising: One or more 2D perovskite crystals; One or more Group I cations or ammonium halides; One or more metal halides; and One or more solvents; and The substrate is annealed to form the perovskite film.

2. The method of claim 1, wherein the annealing comprises heating the substrate to a temperature in the range of room temperature to 200°C.

3. The method according to claim 1, wherein the first group cation or ammonium halide is selected from the group consisting of formamidine halides, cesium halides, guanidine halides, methylammonium halides, and combinations thereof.

4. The method according to claim 1, wherein the metal halide is lead iodide.

5. The method of claim 1, wherein the ink comprises 0.1 to 50 mol% of the 2D perovskite crystals.

6. The method of claim 1, wherein the 2D perovskite crystal comprises having the formula A'A n-1 B n X 3n+1 or A'A n B n X 3n+1 The perovskite, wherein A' is a spacer cation, A is a monovalent cation, B is a divalent metal, n = 1-7, and X is a halide.

7. The method according to claim 6, wherein A' is selected from the group consisting of butylammonium, pentammonium, hexammonium, heptammonium, phenethylammonium, octylammonium, 4-aminomethylpiperidine, 3-aminomethylpiperidine, 3-(aminomethyl)pyridine, butanediamine, and combinations thereof.

8. The method of claim 6, wherein A is selected from the group consisting of formamidine, dimethylammonium, cesium, and guanidine.

9. The method according to claim 6, wherein X is selected from the group consisting of iodides, bromides, chlorides, and combinations thereof.

10. The method according to claim 6, wherein B is selected from the group consisting of lead, germanium, bismuth, copper, silver, gold, gallium, indium, antimony, tin, and combinations thereof.

11. The method according to claim 1, wherein the 2D perovskite is selected from the group consisting of BA2PbI4, BA2FAPb2I7 and combinations thereof.

12. The method of claim 1, wherein the perovskite film comprises FAPbI3.

13. The method according to claim 1, wherein the solvent is selected from the group consisting of dimethylformamide, dimethyl sulfoxide, and combinations thereof.

14. The method of claim 13, wherein the solvent is a mixture of DMF and DMSO provided in a ratio ranging from 1:1 to 9:1 DMF:DMSO.

15. An optoelectronic device comprising a perovskite film formed by the method according to claim 1.

16. The device of claim 15, wherein the optoelectronic device comprises a solar cell.

17. The device of claim 16, wherein the solar cell has an efficiency of at least 23.5%.

18. A perovskite ink comprising: 2D perovskite crystals; Group I cations or ammonium halides; Metal halides; and Solvent.

19. The ink according to claim 18, wherein the first group cation or ammonium halide is selected from the group consisting of formamidine halides, cesium halides, guanidine halides, methylammonium halides, and combinations thereof.

20. The ink of claim 18, wherein the 2D perovskite crystal comprises having the formula A'A n-1 B n X 3n+1 or A'A n B n X 3n+1 The perovskite, wherein A' is a spacer cation, A is a monovalent cation, B is a divalent metal, n = 1-7, and X is a halide.

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