3d / 2d perovskite solar cells

Abstract

The invention is related with 2D passivation layer providing radical impact of electronic and steric effects on performance of 3D / 2D perovskite solar cells.

Description

DESCRIPTION 3D / 2D PEROVSKITE SOLAR CELLS Technical Field The invention is related with 2D passivation layer providing radical impact of electronic and steric effects on performance of 3D / 2D perovskite solar cells. State of the Art Increasing energy demand has encouraged researchers to search for alternative, clean and sustainable energy sources. Among the renewable energy sources such as wind, tidal, solar, hydrothermal, geothermal; solar energy is the most promising one due to its abundance and capability to fulfill very high energy demands. For this purpose. photovoltaic (PV) solar cells were invented to convert sunlight into electricity. Breakthrough of solar cells was achieved in 1954, when the world's first practical silicon solar cell with 6% efficiency was discovered by the scientists in Bell Laboratories. This was the beginning of the first generation of solar cells. which was based on crystalline silicon. Since then, researchers have been investigating more materials to utilize low-cost solar cells, which gave rise to the second generation of solar cells. These cells were mostly based on III-V semiconductors such as cadmium telluride and copper indium gallium selenide.2 Due to the scarcity and toxicity of these materials, third generation of solar cells emerged with the introduction of dye-sensitized solar cells and organic photovoltaics (OPV). Among the third generation, perovskite solar cells (PSCs) are the most promising ones due to their outstanding PV performance, abundancy, easy and low-cost processing. A natural mineral, calcium titanate (CaTiO3) was discovered by Gustav Rose in 1839. This mineral was named after Lev Perovski, who was a Russian mineralogist. Perovskite structure refers to any material with the same crystal structure as CaTiO3. In general, perovskites have ABX3 structure, where ‘A’ is a monovalent cation, ‘B’ is a divalent cation and ‘X’ is an anion that binds to both. For perovskite solar cells, ‘A’ is usually methylammonium (MA, CH3NH3+) or formamidinium (FA, CH(NH2)2+), ‘B’ is usually lead (Pb2+) and ‘X’ is usually halide such as iodine (I-), bromine (Br-) or chlorine (Cl-). Low-dimensional perovskites draw attention due to their unique optoelectronic properties and superior stability. Low-dimensional perovskites are obtained when long alkyl chained A site spacer cations are introduced into the 3-dimensional (3D) perovskites. This leads to tolerance 1   factor becoming larger than 1 because spacer cations have a large ion radius.95 Low- dimensional perovskites are generally expressed in the formula of (A')mAn-1BnX3n+1, where A' can be a divalent (m = 1) or monovalent (m = 2) cation.96 In this formula, n is the number of metal layers that are sandwiched between the organic layers. Band gap and quantum confinement tuning can be managed by changing n. A pure 2-dimensional (2D) layer is achieved when n = 1, whereas a pure 3D perovskite layer is formed when n = ∞. There are various advantages of perovskites. The possibility to form many different structures by changing A, B and X ions creates a huge family of perovskites. This leads to an amazing property of perovskites, which is the fact that their band gap can be tuned by changing A, B and X compounds. Due to the unique properties of perovskites such as having a direct band gap, high absorption coefficients, low exciton binding energy and large dielectric constant, they can be used for variety of optoelectronic applications such as lasers, light-emitting diodes, transistors, and solar cells. Perovskite solar cells function similar to the solid-state p-n junction solar cells. Upon light exposure on PSCs, perovskite layer absorbs photons of wavelength matching its band gap. With the absorption of photons, electrons are excited to the conduction band of perovskite, leaving holes in the valence band, which are also treated as charge carriers. These electrons and holes are collected by the electron transport layer (ETL) and the hole transport layer (HTL), respectively. Free electrons pass from the perovskite layer to the ETL and arrive at the transparent conducting oxide (TCO), which is usually indium tin oxide (ITO), or fluorine doped tin oxide (FTO). Simultaneously, holes travel to the HTL and arrive at the metal electrode. TCO and metal electrodes are connected resulting in the electron flow through the external circuit which generates the photocurrent, and recombination of electrons and holes in the end. PSCs can be fabricated in mesoporous or planar structures. In mesoporous structure, perovskite material is attached to a mesoporous metal oxide scaffold layer. The function of this scaffold is to help photogenerated electrons transfer to the ETL. This structure requires high temperature treatment processes during fabrication. Although the mesoporous device structure was commonly used in the early discoveries, the planar structure attracted more attention lately due to its simplicity. Typical planar device structure consists of a perovskite absorber layer, sandwiched between an HTL and an ETL, with a TCO and metal electrodes. Planar structure can have two different configurations. In regular (n-i-p) planar structure, n- 2   type ETL is coated on top of the TCO, and the light reaches the ETL first, whereas in inverted (p-i-n) structure, p-type HTL is coated on top of the TCO, and the light reaches the HTL first. The device performance is highly related with the choice of transport layers. Transport layers with efficient charge extraction and good transport properties lead to a high-performance cell. A good transport layer must have properties such as proper band alignment with perovskite, high transmittance in the visible region, high carrier mobilities, high stability, easy and low- cost processability. The ETL extracts and transports photogenerated electrons from perovskite to the TCO or the metal electrode, while blocking the hole transport. In addition, the ETL plays a role in the surface modification of the perovskite film and charge recombination mitigation. The ETL must have compatible energy levels with the perovskite in order to facilitate electron transport and enhance the built-in potential. The most commonly used ETLs are titanium dioxide (TiO2) and tin oxide (SnO2) for the n-i-p structure, and [6,6]-phenyl- C61-butyric acid methyl ester (PC61BM) for the p-i-n structure. Other than these materials, fullerene and its derivatives, metal oxides, small organic molecules, and polymers are also used as ETLs. Electron extraction and transport properties of ETLs can further be improved by doping, passivation and using additives or nanoparticles. The HTL transports photogenerated holes from the perovskite to the metal electrode or the TCO, while blocking the electron transport. It reduces charge recombination which results in an increase in selectivity of the contact, and an enhancement of the open-circuit voltage. In addition, the  HTL may prevent the degradation of the cell, since it may act as a moisture resistant layer or metal ion diffusion barrier. Moreover, it facilitates a better coverage of the perovskite layer. The most commonly used HTLs are Spiro-OMeTAD and poly[bis(4-phenyl) (2,5,6- trimethylphenyl)amine] (PTAA) for the n-i-p structure, and poly (3,4-ethylene dioxythiophene):poly (4-styrenesulfonate) (PEDOT:PSS) for the p-i-n structure. Besides these materials, small molecules, polymers, and inorganic molecules are also used as HTLs. The perovskite-based photovoltaic devices have suffered from the instability of cells duo the internal and external factors over the past decade. Scaling up from the cell to the module level, these two factors should essentially be eliminated to be applied by some rational strategies. Utilizing passivation Iayer is the simplest, easiest and the most promising strategy of enhancing the crystallinity of the perovskite bulk and reducing the interface loss by regulating the interface. Through passivation engineering, an improved band alignment, enhanced charge carrier transport, deceased surface defects, and barrier for external stimulus, such as heat, oxygen, and moisture can be achieved.P9IJ Furthermore, the efficiency of PSCs 3   can be boosted by lowering the loss between interfaces whereas the stability of PSCs can be icreased by inhibiting degradation. In addition, passivation engineering has the advantage that a straightforward spin coating process is feasible, therefore it can beutilized to large area PSCs for commercialization. It is essential to understand the fundamental of external degradation mechanism and The interaction with intrinsic degradation reasons causing to associating with the methodologies for the performance of PSCs. Well-known conventional methods such as putting UV-filter and encapsulating constructed devices seem to be a solution for preventing PSCs from external environmental factors. For instance, the illumination of light is known the main initiator for working photovoltaic devices, however the same light also gives rise to break down the perovskite molecules and lead the degradation of perovskite-based solar device performance with the creation of carrier-recombination centres. That's why, finding permanent solutions, causing from the internal cell problems should be the main concern for the researchers, since abovementioned external factors also initiate the internal degradation of PSCs. The internal instability is predominantly triggered by deep defect states. For example, lead (Pb) element at the B site in PSCs can degrade under illumination and at an elevated temperature due to the soft nature of Pb-I bonding and Pb2+ions and so the Pb2+ions produce Pb atoms and create deep defects states which have a negative impact on the interface connections and the transmission of photogenerated carriers. To solve these problems, incorporating protective passivation layers (also named as interfacial layers) between TCO / CTL (where CTL refers to either ETL or HTL), CTL / perovskite interface or CTL / metal electrode interface in PSCs are the most widely used and the most effective strategy.[49l Passivation engineering is primarily applied to reduce the interface defects, which stimulate perovskite degradation. Such engineering enables to lower non- radiative recombination owing to the surface defect passivation of charge transport materials and perovskite materials, improve charge carrier transportation through band alignment, and increase the stability of cells because of the hydrophobicity of the protective interfacial materials used in PSCs. In accordance with this purpose, researchers have been both used commercial and many novel organic (fullerene and non-fullerene-based), and polymeric passivators, followed by incorporation them into PSCs to make comparison between the device performances of PSCs with and without passivation layers. Based on the shared long- term stability results, protective passivation layer(s) utilized between charge transport layers and perovskite light-absorbing layer still is the best strategy. 4   Defects in the cell and the defects caused by the corrosion of the metal contact over time are also detrimental to long-term stability. Several methods have been demonstrated to remedy these issues and 2-dimensional (2D) perovskites have been proposed as one of the most promising groups of materials with increased stability as compared to their 3D counterparts. Phenylethylammonium iodide (PEAI) and butylammonium iodide (BAI) have been widely reported as 2D cations in the literature, although many other 2D cations have been present.

[0015] Recently, halogenated PEAI salts were used for passivation on top of 3D perovskite as pure 2D Ruddlesden-Popper (RP) layered perovskites or interfacial protective layer. In prior art 2D layer formed by 2-(o-fluorophenyl)ethylamine iodide (oFPEAI), 2-(m- fluorophenyl)ethylamine iodide (mFPEAI), and 2-(p-fluorophenyl)ethylamine iodide (pFPEAI) were introduced atop their 3D perovskite and reported over 20% PCE with improved stability under continuous illumination for 1440 h. Figures Figure 1: Schematic representation of (a) molecular structure (b) table of possible molecules Figure 2: Schematic representation of counter ion alternatives Figure 3: Phenylethylammonium salts with mono-substitution Figure 4: Phenylethylammonium salts with di-substitution Figure 5: Phenylethylammonium salts with three-substitution Figure 6: Phenylethylammonium salts with four-substitution Figure 7: Phenylethylammonium salts with five-substitution where R is not hydrogen Figure 8: A. Illustration of the solar cell architecture. B. Schematics of the o-OMe-PEAI, m-OMe-PEAI, and p-OMe-PEAI structures. C. XRD pattern of the reference (ref.) 3D perovskite and perovskites treated with methoxy substituted salts (o-OMe-PEAI, m-OMe-PEAI, and p-OMe-PEAI).002, 040, and 001 represent the diffraction peaks of 2D (n = 1), quasi 2D (n = 2), and PbI2 (001), respectively. D. GIWAXS images of the 3D perovskite. E. GIWAXS images of the 3D / 2D perovskite films. 5   Figure 9: XRD pattern of the pure 2D films (n=1) of o-OMe-PEAI, m-OMe-PEAI, and p- OMe-PEAI Figure 10. XRD pattern of the quasi 2D film (n=2) of o-OMe-PEAI. Figure 11. GIWAXS spectra of the pure 2D films (n=1) of o-OMe-PEAI, m-OMe-PEAI, and p-OMe-PEAI Figure 12: Film Characterization A–D. SEM top-view and cross-section images of the 3D film (A) and 3D / 2D films with o-OMe- PEAI (B) m-OMe-PEAI (C), and p-OMe-PEAI (D). E. Steady-state photoluminescence (PL) spectra. F. Time-resolved PL (TRPL) traces. G. Absorption spectra of the 3D film and 3D films with OMe-PEAI treatment. Figure 13: PL spectra of the pure 2D films (n=1) of o-OMe-PEAI, m-OMe-PEAI, and p- OMe-PEAI Figure 14. Device parameters and molecular dynamics A–D (A) VOC, (B) JSC, (C) FF, and (D) PCE statistics of reference (3D) and 3D / 2D solar cells (out of 5 devices). Box plot details: bottom and top edges of the box indicate 25th and 75th percentiles, respectively. The central horizontal line in the box indicates median, whiskers extend to the most extreme data points, and mean is indicated by open symbols. E. J-V curves of the champion ref. and 3D / 2D solar cells. F. EQE spectra of the champion ref. and 3D / 2D solar cells. Figure 15. a-d) Statistics of reference and 3D / 2D films; e) J-V Curves of the pristine and halogenated PEAI treated devices simulated under one sun illumination; f) EQE spectra and calculated photocurrent values. Figure 16. a) Steady-state photoluminescence spectra, (b) Time-resolved PL traces, and (c) Transmission spectra of reference and meta-halogenated PEAI salt-treated 3D perovskite film. Brief Description of the Invention 2D perovskites are formed by the presence of large ammonium salts with a size exceeding the tolerance factor of the inorganic crystal lattice, thus preventing the continuity of the 3D 6   framework that results in well-defined 2D fragments. Despite their remarkable stability, their high exciton binding energies, poor charge separation characteristics, and large bandgap proved unfavorable for device performance in terms of efficiency Modification of 3D perovskites with a 2D counterpart (3D / 2D) has been investigated to improve stability without compromising efficiency. Various organic ammonium salts have been used to produce efficient 3D / 2D solar cells, but efforts mainly concentrated on halogenated analogues of PEAI salts. Studies regarding the effect of functional group position on the aromatic moiety of PEAI-based salts were also performed. Strongly electron-releasing group substitution is widely used in the design of hole transport materials due to their ability to stabilize holes and defect-passivating character through their uncoordinated lone pairs. Taking these advantages into account, the electron donating groups are also preferred in large organic ammonium salt design for 2D / 3D perovskites as they have the potential to enhance hole extraction and create favorable interactions sites with uncoordinated Pb2+ ions on the surface of 3D perovskite. To date, the methoxy (OMe) substituted organic ammonium salts have not been utilized in the 3D / 2D perovskite solar cells. The effect of -OMe substitution position (-ortho, -meta, and -para) on 2D PEAI salts and their effects on the performance and long-term stability of 3D / 2D PSC have not been investigated in the prior art. Figures 1-7 represents the possible but not limiting alternatives of ammonium salt designed for 2D perovskite layer generation. R is, halogen or aromatic group or alkoxy group, alkyl group, thiol or amine or hydrogen, except all is hydrogen. X may be Iodide, Bromide or Chloride, acetate, triflate, nitrate, alkylsulfate, alkylphosphate, amino acid, tetracyanoborate, dicyanamide, tricyanomethanide, carboxylate, hexaflorophospate, tetrafloroborate, tetrafloromethylacetate, bis(trifloromethanesulfony) imide In the invention, three methoxy-substituted organic ammonium salts named 2-methoxy-PEAI (o-OMe-PEAI), 3-methoxy-PEAI (m-OMe-PEAI), and 4-methoxy-PEAI (p-OMe-PEAI) are synthesized with a straightforward synthetic methodology and utilized in3D / 2D PSCs with (Cs0.04FA0.85MA0.11)Pb(I0.96Br0.01Cl0.03)3 triple-cation perovskites. The position effect of the methoxy-substituted ammonium salts on device performances and the stability of the 3D / 2D PSCs are elucidated. X-ray diffraction (XRD) and grazing-incidence wide-angle X-ray 7   scattering (GIWAXS) results reveal that a 2D layer on the 3D perovskite is formed independently of the -OMe position. Photoluminescence (PL) and time-resolved PL (TRPL) analyses show that films treated with methoxy-substituent salts remarkably decrease trap density and enhance carrier lifetime. Significant enhancement in PCE is achieved for all salts, with o-OMe-PEAI leading the pack (21.35%–23.34%). Enhancements of fill factor (FF) and open circuit voltage (VOC) upon salt treatment are explained by drift-diffusion simulations. Density functional theory (DFT) analyses reveal that o-OMe-PEAI-treated films have the lowest formation energy, forming a super stable interface, thus enhancing device performance as well as long-term stability. In another embodiment of the invention, a collection of halogenated PEA+ cations (x-XPEA+ where x: ortho (o), meta (m), para (p), X: F, Cl, Br) were synthesized by a robust and facile method and deposited on top of 3D perovskite. The 2D perovskite layer formation is confirmed by XRD and GIWAXS analyses for all cations regardless of the nature and position of the halogens. DFT analysis reveals that lower formation energies and higher interfacial dipoles achieved by m-substituted cations are responsible for enhanced performance compared to their -o and -p counterparts. The m-BrPEAI-treated device shows a champion efficiency of 23.42% with a VOC of 1.13 V and FF of 81.2%. This comprehensive study provides guidelines for understanding the phenomena behind the interaction of large cations with 3D Perovskite and their influence on performance and stability. Detailed Description of the Invention 2D passivation layer of OMe-PEAI Device architecture: The solar cells were fabricated in FTO / cp-TiO2 / mp-TiO2 / SnO2 / perovskite / OMe-PEAI / Spiro- OMeTAD / Au architecture as shown in Figure 8. A 3D triple-cation perovskite absorber layer is employed, and a solution ofmethoxysubstituted salts in isopropanol (IPA) was coated on it by spin coating to form the 3D / 2D perovskite structure. The FTO glass substrates (Nippon sheet glass, TEC9AX) were cleaned with Hellmanex, deionized water, acetone, and IPA for 15 min, respectively. Then, substrates were treated with UV-ozone for 15 min. TiO2 solution was prepared by dilution of titanium diisopropoxide bis(acetylacetonate) solution with IPA at a 1:15 vol ratio. The compact layer (c-TiO2) was deposited on the FTO substrates by spray pyrolysis at 450°C and followed by in situ 8   annealing for 30 min. The mesoporous TiO2 (m-TiO2) solution was prepared by dissolving 1g TiO2paste in 10.5 mL ethanol and stirring overnight. Then, the m-TiO2 layer was deposited at 4,500 rpm for 20 s. After annealing at 125°C for 30 min, the m-TiO2 films were gradually heated to 500°C in air, then annealed at 500°C for 20 min. The SnO2 layer was prepared by spin coating 0.1 M SnCl4 solution at 3,000 rpm for 20 s; then, the substrates were annealed for 10 min at 150°C and 1 h at 190°C. Before use, the FTO / c-TiO2 / m-TiO2 / SnO2 substrates were treated with UV-ozone for 30 min. The precursor solution was prepared by dissolving PbI2 (1.35 M), CsI (0.05 M), FAI (1.12 M), MABr (0.05 M), and MACl (0.10 M) in a mixed solvent of DMF:DMSO = 4:1 (volume ratio). Then, 25 mL perovskite precursors were coated onto the FTO / c-TiO2 / m-TiO2 / SnO2 substrates (around 1.4 3 2.4 cm) by spin-coating method, and the coating procedure was performed through a two-step program running at 1,000 and 4,000 rpm for 12 and 25 s, respectively. During the second step (at the 11th second), 750 mL chlorobenzene as an antisolvent was injected quickly onto the substrates. Afterward, the films were annealed at 100_C for 45 min. After cooling to room temperature, a solution of x-OMe-PEAI in IPA (10 mg / mL) was spin coated on the substrate at 4,000 rpm for 15 s. Then, the HTM solution was prepared by mixing a stock solution of spiro-OMeTAD in chlorobenzene with solutions of 4- tert-butylpyridine, Li[TFSI] and Co[t-BuPyPz]3[TFSI]3 (FK209, Dyesol) in acetonitrile with a molar ratio of spiro-OMeTAD:FK209:Li[TFSI]:4-tert-butylpyridine (TBP) at 1:0.03:0.5:3.3. 40 mL spiro-OMeTAD solution was deposited at 3,500 rpm for 20 s on the perovskite film as the hole-transport layer. Finally, a 70-nm-thick gold layer was evaporated as a counter electrode to complete the device fabrication. Synthesis of CompoundsScheme 1. Synthetic Route for Syntheses of o-OMe-PEAI, m-OMe-PEAI, p-OMe-PEAI Successful syntheses of ortho-, meta-, para-methoxy substituted phenyl ethan-1-amine (o- OMe-PEA, m-OMe-PEA, p-OMe-PEA) were conducted in accordance with the literature.2,3 Then, the resulting materials (7.2 mmol) were dissolved in ethanol (7 mL) and the reaction was cooled to 0°C. HI (7.9 mmol, 57 wt. % in H2O) was added slowly and the reaction mixture was stirred for 2 hours at this temperature. The reaction mixture was concentrated 9   under reduced pressure and the products were precipitated by addition of cold Et2O (50 mL). The crude product was dissolved in a minimum amount of ethanol and reprecipitated with cold Et2O to obtain the target salts with high purity. 2-(2-Methoxyphenyl)ethan-1-aminium iodide (o-OMe-PEAI) Yield 63%. White solid. 1H NMR (400 MHz, DMSO): δ 7.75 (s, 3H), 7.30-7.11 (m, 2H), 7.03-6.84 (m, 2H), 3.80 (m, 3H), 3.03-2.91 (m, 2H), 2.86-2.81 (m, 2H); 13C NMR (100 MHz, DMSO): δ 157.6, 130.6, 128.8, 125.3, 120.9, 111.3, 55.9, 28.5. 2-(3-Methoxyphenyl)ethan-1-aminium iodide (m-OMe-PEAI) Yield 65%. White solid.1H NMR (400 MHz, DMSO): δ 7.76 (s, 3H), 7.25 (t, J=8.0 Hz, 1H), 6.82 (d, J=7.5 Hz, 3H), 3.74 (s, 3H), 3.07 (d, J= 7.1 Hz, 2H), 2.84-2.79 (m, 2H); 13C NMR (100 MHz, DMSO): δ 159.4, 138.7, 129.7, 120.8, 114.3, 112.2. 2-(4-Methoxyphenyl)ethan-1-aminium iodide (p-OMe-PEAI) Yield 32%. White solid.1H NMR (400 MHz, DMSO): δ 7.74 (s, 3H), 7.17 (d, J=8.5 Hz, 2H), 6.89 (d, J=8.6 Hz, 2H), 3.72 (s, 3H), 3.05-2.95 (m, 2H), 2.84-2.68 (m, 2H); 13C NMR (100 MHz, DMSO): δ 158.1, 129.7, 128.9, 114.0, 55.1, 32.1. Fabrication of 2D perovskite films For the fabrication of pure 2D films, the x-OMe-PEAI salts were mixed with PbI2 in a 2:1 (molar) ratio and dissolved in DMF:DMSO mixture = 4:1 (volume ratio). For quasi-2D perovskite film, o-OMe-PEAI (2M),MAI (1M), and PbI2 (2 M) were mixed and dissolved in DMF:DMSO = 4:1 (volume ratio). Then, all the substrates were coated at 1,000 and 4,000 rpm for 12 and 25 s, respectively, on electron transport layers (ETLs). The films were annealed at 100°C for 45 min Crystallographic features The XRD spectra displayed a peak below 10° for all 3D / 2D films, which is attributed to the formation of a low-dimensional top perovskite layer. The observed peaks at 2Ɵ = 4.92°, 4.97°, and 4.90° for salt-treated 3D perovskites (Figure 8C) are consistent with pure (OMe- PEAI)2PbI42D perovskite (n = 1) peaks (4.97°, 4.91°, and 4.94°) with slight (<0.06°) shifts (Figure 9). Moreover, a significant decrease in PbI2 peak intensity (2Ɵ = 12.7°) was observed for films treated with OMe-PEAI, indicating that organic ammonium salts interact with excess PbI2 on the 3D perovskite surface, providing further strong evidence of 2D layer formation.26,27 Additional peak observed for o-OMe-PEAI at 2Ɵ = 7.55° ((040) oriented) arises from quasi-2D perovskite structure with n = 2 (Figure 10). 10   Since crystallographic orientation affects the optoelectronic properties and overall stability of devices,29 GIWAXS measurements were carried out with a 0.2° incident angle to reveal the crystal orientation of perovskite components. The strong scattering rings at qz = 1 and 0.9 Å-1belong to the (110)-oriented crystal plane of the 3D perovskite and the (001)-oriented PbI2 crystal plane31 (Figure 8D), respectively. The scattering ring of PbI2 decreases gradually, and a new spot appears at qz= 0.3 Å-1upon insertion of an o-OMe-PEAI salt on the 3D perovskite (Figure 8E). The pure 2D film of o-OMe-PEAI ((OMe-PEAI)2PbI4) also has strong spots around qz= 0.3 and 0.6 Å-1, which confirms the formation of the proposed 2D layer (Figure 11). Film characteristics The surface morphologies of the films upon treatment with -OMe salts were changed, as shown by top-view scanning electron microscopy (SEM) images in Figures 12A–12D. A higher contrast of the 3D film (Figure 12A) and the observation of bright grain sites refer to the presence of excess PbI2 on the surface. Contrarily, perovskite films treated with methoxy- substituent salts have fewer bright grains on the surface, indicating that OMe-PEAI salts react with excess PbI2on the 3D perovskite surface (Figures 12B–5D). It should be noted that the 2D layers are not distinguished in cross-section SEM due to their very thin nature (Figures 12B–12D). All 3D / 2D perovskites have higher PL intensities (Figure 12E) and longer PL decay times (Figure 12F; Table 1) compared with the 3D reference film, indicating that OMe- PEAI salts suppress the nonradiative recombination and decrease defect density in the perovskite layer and / or grain boundaries. Table 1: Fitting parameters of TRPL spectra of reference and OMe-PEAI-treated films, A1 and A2 are the fractions of the two decay processes and T1 and T2 are shorter and longer lifetimes, respectivelyParticularly, film with o-OMe-PEAI salt shows a significant increase in PL intensity and lifetime, implying that ortho-positioned salt provides superior passivation of effects than the meta and para methoxy-substituted ammonium salts. No PL signal was detected at lower wavelengths for the corresponding high-band-gap 2D perovskites due to the low concentration of the salt in the solution, which results in a very thin layer of 2D perovskite. 11   Absorption spectra showed no significant change in absorption for 3D / 2D films compared with 3D only, revealing that 2D materials do not incorporate into 3D perovskite bulk, which is also in line with XRD and GIWAXS analyses. See Figure 13 for the spectra of pure 2D films. Photovoltaic performance and DFT calculations Significant improvements in VOC and FF were observed for 3D films treated with OMe- PEAI salts (Figures 14A and 14C), in line with the steady-state PL and TRPL studies and inferring superior charge transport, respectively. In addition, a slight increase in the short circuit current (JSC) was also observed for the 3D- / 2D-based solar cells (Figure 14B). Average efficiencies for the reference, o-OMe-PEAI, m-OMe-PEAI, and p-OMe-PEAI PSCs were obtained as 20.86%, 23.08%, 21.79%, and 22.25%, respectively (Figure 14D). All solar cells fabricated in this work showed a limited deviation in all device parameters, showcasing the reproducibility of the device fabrication processes (Table 2). Table 2: Voc, Jsc, FF and PCE statistics of reference(3D) and 3D / 2D solar cells Theand p- OMe-PEAI and of the reference are 23.34%, 22.25%, 22.62%, and 21.35%, respectively (Figure 14E). All 3D / 2D PSCs treated with methoxysubstituted salts showed lower hysteresis than the reference solar cell, indicating suppressed ion migration and accumulation by passivating the defects on the perovskite surface. It should be noted that the JSC values obtained from the current-voltage (J-V) curves and external quantum efficiency (EQE) spectra have a good agreement, as shown in Figures 14E and 14F. Finally, the DFT calculations confirm that o-OMe-PEA has the highest energy of iodine vacancy formation among the three tested interfaces, which is also in line with the hypothesis on the reduced concentration of trap states (Table 3). The order of iodine vacancy formation energy correlates with the device performance, supporting the above-mentioned hypotheses. 12   Table 3. The formation energies of neutral I vacancies at the respective interfaces. Interface ΔfEvacI, eV o-OMe-PEAI 3.83 The ionization energieso t e re erence an ms were extracted using the ultraviolet photoelectron spectroscopy (UPS) as -5.49, -6.03, -6.19, and -6.03 eV for the reference, o- OMe-PEAI, m-OMe-PEAI, and p-OMe-PEAI, respectively. The highest occupied molecular orbital (HOMO) level energy of the 3D / 2D films is lower than the HOMO level of the reference film, which results in an improved solar cell performance despite a stronger mismatch with the transport layer. Two possible explanations for these observations are that (1) the lowered energy levels imply a decrease in n-character upon salt treatment and cause band bending, thus improving charge transport properties, and / or (2) holes are tunneling through the 2D layers to reach the hole transport layer, as evidenced by increased VOC and FF. It has been shown that inserting a very thin layer of an even insulating layer into PSCs improves device performance through enhanced charge carrier lifetime and FF. 2D passivation layer of x-RPEAI salt Second group of compounds of the invention are a series of large bulky organic cations based on phenylethylammonium (PEA) frameworks with three different halogens (-F, -Cl, and -Br) located at -ortho (-o), -meta (-m), and -para (-p) positions on the aromatic benzene ring of corresponding x-RPEAI salts. There are various studies related to PEAI-type salts regarding the effect of substituents or their positions on the performance of PSCs in the literature. Detailed systematic analysis and efforts towards a fundamental understanding of the nature and the position of the substituents of 2D forming salts on the performance of 3D / 2D PSCs still need to be included. Phenylethylammonium (PEA) frameworks with three different halogens (-F, -Cl, and -Br) located at -ortho (-o), -meta (-m), and -para (-p) positions on the aromatic benzene ring of corresponding x-RPEAI salts were synthesized with a straightforward method and utilized as a 2D perovskite layer on the surface of CsFAMA-based 3D triple cation perovskite. It is proved the formation of 2D layers for all 9 salts through X-ray diffraction (XRD) and grazing 13   incident wide-angle X-ray scattering (GIWAXS) analyses. Additionally, photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy techniques were investigated and showed that a 2D perovskite layer based on m-XPEA2PbI4, deposited on top of 3D perovskite suppresses nonradiative carrier recombination more effectively than the reference and their -ortho and -para analogs. Among these 9 different 2D perovskites, m- XPEA2PbI4had higher interfacial dipoles and lower formation energies on the 3D perovskite surface, proved by detailed DFT analyses. A combination of experimental and theoretical studies of halogen substitutions at the meta-positioned benzene rings of 2D PEAI salts results in higher (1.13 V) and FF (over 81%), thereby an enhanced power conversion efficiency exceeding 23%.   The o-, m-, and p-halogenated phenylethylammonium cations (x-XPEA+) were synthesized by the developed robust and facile method in high yields (over 85% in average). To the best of our knowledge, such a straightforward three-step synthesis protocol was applied to produce large bulky organic cations, starting from widely available aromatic aldehyde derivatives for the first time. The three different large bulky organic cations (o-ClPEA+, m-ClPEA+and m-BrPEA+), which have not been tested in PSCs, could be produced by the abovementioned straightforward method. For all device architectures, (Cs0.04FA0.85MA0.11)Pb(I0.96Br0.01Cl0.03)3)-based triple cation 3D perovskite composite was utilized and deposited via traditional spin coating method. The synthesized x-RPEAI salts were individually coated on top of the 3D perovskite to construct 3D / 2D hybrid structures using the same method. Syntheses of o, m, and p-Halogen-Substituted Nitrovinylbenzene (x-RNVB where x: o, m, p and R: F, Cl, Br) Frameworks The systematic syntheses of the target o-, m-, and p-halogen-substituted nitrovinylbenzene scaffolds (x-RB-CH=CH-NO2or simply x-RNVB where x: o, m, p and X: F, Cl, Br) starting from their commercial benzaldehyde forms (x-RB-CH=O or simply x-RBA) were performed via Henry Reaction according to the literature with small modifications. The empty well-dried reaction flasks with suitable sizes were separately vacuumed and filled with inert gas (ie, argon (Ar), nitrogen (N2)) three times. Then, ammonium acetate (NH4OAc, 2.0 eq.) was added to these reaction flasks, and dissolved in acetic acid (AcOH, 10 eq.). After that, nitromethane (CH3NO2, 5.0 eq.) which was extra dried over molecular sieves for several days, was transferred to the resultant solutions. Into these solutions, x-RBA (1.0 eq.) was added dropwise. The reaction mixtures were stirred at 90 °C under inert atmosphere and dark environment. The reaction progresses for each experiment were individually monitored with thin layer chromatography (TLC) technique. Typically, 3 h was enough to disappear of starting materials (x-RBA) and appeared a very broad dominant spot that belonged to the target nitro-aldol product (x-RNVB). Upon completion of reactions, AcOH and CH3NO2in the 14   reaction mixtures were evaporated under reduced pressure, followed by pouring H2O into the remaining residue. The resultant suspensions were extracted with dichloromethane (DCM or CH2Cl2) three times. The combined organic phases were sequentially dried over anhydrous sodium sulfate (Na2SO4), filtered over filter paper, and then evaporated under reduced pressure. The residual mixtures were purified by Silica Gel Column Chromatography with a suitable solvent system. The purified halogenated nitroaldol frameworks (x-RNVB) were collected in a glass vial and dried under vacuum at room temperature for minimum 30 minutes. The isolated target x-RNVB materials were separately achieved as individual colors and stored in an Ar- or N2-filled vials for the next step. o-Fluoronitrovinylbenzene (o-FNVB). Yield 89%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 8.06 (d, J = 13.8 Hz, 1H), 7.74 (d, J = 13.8 Hz, 1H), 7.59 – 7.44 (m, 2H), 7.26 (t, J = 7.5 Hz, 1H), 7.23 – 7.14 (m, 1H);13C NMR (100 MHz, CDCl3): δ 163.0, 160.5, 139.3, 139.1, 133.7, 133.6, 132.4, 131.3, 125.0, 124.9, 118.3, 118.2, 116.6, 116.4. m-Fluoronitrovinylbenzene (m-FNVB). Yield 92%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 13.7 Hz, 1H), 7.57 (d, J = 13.7 Hz, 1H), 7.45 (q, J = 7.8 Hz, 1H), 7.35 (d, J = 7.7 Hz, 1H), 7.29 – 7.14 (m, 2H);13C NMR (100 MHz, CDCl3): δ 164.1, 161.6, 138.0, 137.6, 132.1, 132.0, 131.0, 130.9, 125.1, 125.0, 119.1, 118.8, 115.4, 115.2. p-Fluoronitrovinylbenzene (p-FNVB). Yield 86%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 7.98 (d, J = 13.7 Hz, 1H), 7.64 – 7.47 (m, 3H), 7.15 (t, J = 8.5 Hz, 2H);13C NMR (100 MHz, CDCl3): δ 166.1, 163.5, 137.8, 136.7, 131.3, 131.2, 126.2, 126.2, 116.8, 116.6. o-Chloronitrovinylbenzene (o-ClNVB). Yield 86%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 8.41 (d, J = 13.7 Hz, 1H), 7.66 – 7.56 (m, 2H), 7.50 (d, J = 1.4 Hz, 1H), 7.43 (t, J = 1.7 Hz, 1H), 7.34 (t, J = 1.2 Hz, 1H);13C NMR (100 MHz, CDCl3): δ 138.7, 135.9, 135.0, 132.8, 130.6, 128.5, 128.3, 127.4. m-Chloronitrovinylbenzene (m-ClNVB). Yield 89%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 7.94 (d, J = 13.7 Hz, 1H), 7.59 (s, 1H), 7.54 – 7.52 (m, 1H), 7.51 – 7.46 (m, 1H), 7.45 (s, 1H), 7.44 – 7.41 (m, 1H);13C NMR (100 MHz, CDCl3): δ 137.9, 137.4, 135.3, 131.9, 131.7, 130.6, 128.7, 127.2. p-Chloronitrovinylbenzene (p-ClNVB). Yield 86%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 7.96 (d, J = 13.7 Hz, 1H), 7.62 – 7.55 (m, 1H), 7.55 – 7.40 (m, 4H);13C NMR (100 MHz, CDCl3): δ 138.4, 137.8, 137.5, 130.4, 129.9, 128.7. o-Bromonitrovinylbenzene (o-BrNVB). Yield 88%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 8.40 (d, J = 13.7 Hz, 1H), 7.69 (dd, J = 7.6, 1.7 Hz, 1H), 7.58 (dd, J = 6.4, 1.2 Hz, 1H), 7.54 (d, J = 15   13.8 Hz, 1H), 7.43 – 7.29 (m, 2H);13C NMR (100 MHz, CDCl3): δ 138.7, 137.5, 133.9, 132.9, 130.2, 128.4, 128.1, 126.3. m-Bromonitrovinylbenzene (m-BrNVB). Yield 91%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 7.93 (d, J = 13.7 Hz, 1H), 7.69 (s, 1H), 7.62 (d, J = 7.2 Hz, 1H), 7.56 (d, J = 13.7 Hz, 1H), 7.48 (d, J = 7.8 Hz, 1H), 7.34 (t, J = 7.9 Hz, 1H);13C NMR (100 MHz, CDCl3): δ 138.1, 137.4, 134.9, 132.1, 131.7, 130.9, 127.7, 123.4. p-Bromonitrovinylbenzene (p-BrNVB). Yield 94%. Yellow solids.1H NMR (400 MHz, CDCl3): δ 7.94 (d, J = 13.7 Hz, 1H), 7.65 – 7.52 (m, 3H), 7.42 (d, J = 8.5 Hz, 2H);13C NMR (100 MHz, CDCl3): δ 137.8, 137.5, 132.8, 130.4, 128.9, 126.8. Syntheses of o, m, and p-Halogen-Substituted Phenylethylamine (x-RPEA where x: o, m, p and R: F, Cl, Br) Frameworks The systematic syntheses of the target o-, m-, and p-halogen-substituted phenylethylamine scaffolds (x-RB-CH2CH2-NH2or simply x-RPEA where x: o, m, p and R: F, Cl, Br) starting from previously- synthesized aromatic nitrovinylbenzene products (x-RNVB) were performed via reduction reaction using LiAlH4according to the literature with small modifications.[22,23]The empty well-dried reaction flasks with suitable sizes were separately vacuumed and filled with inert gas (ie, argon (Ar), nitrogen (N2)) three times. Then, lithium aluminum hydride (LAH or LiAlH4, x g, 4.0 eq.) was carefully transferred to these flasks at room temperature and followed by dropwise addition of suitable dry diethyl ether (Et2O) at 0 °C. To different empty flasks, which were well-dried and filled with the selected inert gas, a precursor was prepared by transferring the corresponding x-RNVB molecules (2.0 g, 1.0 eq.) and dissolving them in the chosen reaction solvent (Et2O). If the solubility of x-RNVB was not good at this solvent, then heat gun was used while stirring. To avoid an explosion resulted from highly volatile organic vapors, an extra precaution was taken by giving an output to the system. The prepared precursors were slowly added to the corresponding reaction flasks including reduction suspension (LiAlH4 / reaction solvent: Et2O) at 0 °C. Then, these mixtures were stirred at near the reflux temperature of reaction solvent for 3 h under Ar atmosphere. Upon completion of reactions, the reaction temperatures were cooled to 0 °C. The subsequent mixtures were diluted with Et2O, followed by quenching with slow addition of H2O (x mL), 15% aqueous NaOH solution (x mL), and H2O (3x mL) respectively. The resultant mixtures were sequentially dried over anhydrous Mg2SO4and filtered over filter paper. The obtained residues were excessively washed with Et2O. The combined organic phases were evaporated under reduced pressure. The crude halogenated aromatic phenylethylamine frameworks (x-RPEA) were individually achieved in the form of liquids with distinctive colors were freshly used for the next step without making any further purification. 16   o-Fluorophenylethylamine (o-FPEA). Yield 72%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.26 – 7.11 (m, 2H), 7.11 – 6.94 (m, 2H), 3.08 – 2.85 (m, 2H), 2.82 (t, J = 6.7 Hz, 2H), 2.60 (s, 2H);13C NMR (100 MHz, CDCl3): δ 162.5, 160.1, 131.1, 131.1, 128.0, 127.9, 126.6, 126.4, 124.0, 124.0, 115.4, 115.2, 42.2, 33.3. m-Fluorophenylethylamine (m-FPEA). Yield 84%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.35 – 7.21 (m, 1H), 7.01 (d, J = 7.6 Hz, 1H), 6.95 (d, J = 9.1 Hz, 2H), 3.00 (t, J = 6.9 Hz, 2H), 2.78 (t, J = 6.8 Hz, 2H), 1.69 (s, 2H);13C NMR (100 MHz, CDCl3): δ 162.8, 160.3, 141.1, 141.0, 128.6, 128.5, 123.1, 123.1, 114.3, 114.1, 111.6, 41.8, 38.2. p-Fluorophenylethylamine (p-FPEA). Yield 72%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.22 – 7.03 (m, 2H), 6.95 (t, J = 8.7 Hz, 2H), 2.91 (t, J = 6.9 Hz, 2H), 2.69 (t, J = 6.9 Hz, 2H), 1.83 (s, 2H);13C NMR (100 MHz, CDCl3): δ 162.7, 160.3, 135.3, 135.3, 130.2, 130.1, 115.1, 43.5, 39.0. o-Chlorophenylethylamine (o-ClPEA). Yield 77%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.17 – 7.06 (m, 3H), 6.97 (d, J = 6.9 Hz, 1H), 2.85 (t, J = 6.9 Hz, 2H), 2.63 (t, J = 6.9 Hz, 2H), 2.57 (s, 2H);13C NMR (100 MHz, CDCl3): δ 141.6, 134.2, 129.7, 128.9, 127.0, 126.5, 43.0, 39.1. m-Chlorophenylethylamine (m-ClPEA). Yield 88%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.34 (d, J = 7.5 Hz, 1H), 7.24 – 7.12 (m, 3H), 3.02 – 2.90 (m, 2H), 2.88 (t, J = 6.7 Hz, 2H), 2.03 (s, 2H);13C NMR (100 MHz, CDCl3): δ 137.3, 134.2, 131.0, 129.6, 127.7, 126.8, 41.9, 37.7. p-Chlorophenylethylamine (p-ClPEA). Yield 83%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.25 (d, J = 7.8 Hz, 2H), 7.11 (d, J = 8.1 Hz, 2H), 2.93 (t, J = 6.9 Hz, 2H), 2.70 (t, J = 7.0 Hz, 2H), 1.75 (s, 2H);13C NMR (100 MHz, CDCl3): δ 138.2, 132.0, 130.2, 128.6, 43.3, 39.2. o-Bromophenylethylamine (o-BrPEA). Yield 80%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.53 (d, J = 7.8 Hz, 1H), 7.26 – 7.17 (m, 2H), 7.10 – 7.02 (m, 1H), 2.99 – 2.92 (m, 2H), 2.88 (t, J = 6.3 Hz, 2H), 1.64 (s, 2H);13C NMR (100 MHz, CDCl3): δ 139.0, 132.9, 130.9, 128.0, 127.4, 124.7, 42.1, 40.3. m-Bromophenylethylamine (m-BrPEA). Yield 85%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.51 – 7.28 (m, 1H), 7.23 – 6.98 (m, 3H), 2.86 (t, J = 6.9 Hz, 2H), 2.63 (t, J = 6.9 Hz, 2H), 1.78 (s, 2H);13C NMR (100 MHz, CDCl3): δ 142.1, 131.8, 130.0, 129.3, 127.5, 122.5, 43.2, 39.6. p-Bromophenylethylamine (p-BrPEA). Yield 74%. Yellowish liquid.1H NMR (400 MHz, CDCl3): δ 7.40 (d, J = 8.3 Hz, 2H), 7.06 (d, J = 8.3 Hz, 2H), 2.92 (t, J = 6.9 Hz, 2H), 2.68 (t, J = 6.9 Hz, 2H), 1.51 (s, 2H);13C NMR (100 MHz, CDCl3): δ 138.8, 131.5, 130.6, 120.0, 43.4, 39.4. 17   Syntheses of o, m, and p-Halogen-Substituted Phenylethylammonium Iodide (x-RPEAI where x: o, m, p and R: F, Cl, Br) Salts The systematic syntheses of the target aromatic o-, m-, and p-halogen-substituted phenylethylammonium iodide scaffolds (x-XB-CH2CH2-NH3I or simply x-RPEAI where x: o, m, p and R: F, Cl, Br) salts starting from previously synthesized aromatic phenylethylamine molecules (x- XPEA) were performed with the treatment of HI (57 wt.% aqueous solution) according to the literature with small modifications.[24–27]The different x-XPEA molecules (1.0 eq.) were separately added to the empty reaction flasks (50 mL) and then dissolved in ethanol (EtOH, 5.0 mL). Later, aqueous solution of hydriodic acid (HI, 1.05 eq.57.0 wt.% in H2O) was added slowly to the resulting solutions under ice bath condition. The reaction mixtures were stirred at 0 °C for 1 h under Ar atmosphere and then allowed to be warmed up to room temperature by removing the ice bath. Then, the reaction solvent and excess amount of HI were evaporated under reduced pressure at 60 °C. The subsequent brown solids were thoroughly washed with Et2O until any color change was observed. If it was realized that so much Et2O was needed to purify the crude salts, then washing procedure was stopped and continued with implementation of precipitation procedure. This procedure was applied by keeping the unpurified salts in Et2O at refrigerator for at least one day to slow down and control the precipitation of pure salts. The obtained pure precipitates were filtered over filter paper and washed with Et2O once again. An extra purification was also done by recrystallization with EtOH. Upon completion of recrystallization, extra pure crystals were filtered over filter paper and washed with Et2O for the last time. These pure salt crystals were transferred to a glass vial, and then dried either at open air atmosphere, followed by extra drying under vacuum at room temperature. The isolated target aromatic halogen-substituted phenylethylammonium iodide (x-RPEAI) salts were achieved as individual colors and stored in an N2-filled glovebox for the perovskite solar cell (PSC) studies. o-Fluorophenylethylammonium Iodide (o-FPEAI). Yield 85%. Yellow solids.1H NMR (400 MHz, DMSO-d6): δ 7.83 (s, 3H), 7.38 – 7.29 (m, 2H), 7.24 – 7.14 (m, 2H), 3.08 – 2.98 (m, 2H), 2.94 – 2.85 (m, 2H);13C NMR (100 MHz, CDCl3): δ 161.7, 159.3, 131.1, 131.1, 129.1, 129.0, 124.7, 124.6, 123.8, 123.7, 115.4, 115.2, 26.4, 26.4. m-Fluorophenylethylammonium Iodide (m-FPEAI). Yield 91%. Yellowish solids.1H NMR (400 MHz, DMSO-d6): δ 7.78 (s, 3H), 7.42 – 7.35 (m, 1H), 7.19 – 7.03 (m, 3H), 3.14 – 3.02 (m, 2H), 2.93 – 2.83 (m, 2H);13C NMR (100 MHz, CDCl3): δ 163.4, 161.0, 140.0, 139.9, 130.5, 130.5, 124.9, 124.9, 115.6, 115.4, 113.7, 113.5, 32.5, 32.5. p-Fluorophenylethylammonium Iodide (p-FPEAI). Yield 84%. Yellowish solids.1H NMR (400 MHz, DMSO-d6): δ 7.77 (s, 3H), 7.41 – 7.21 (m, 2H), 7.20 – 7.00 (m, 2H), 3.16 – 2.93 (m, 2H), 2.93 – 18   2.72 (m, 2H);13C NMR (100 MHz, CDCl3): δ 162.7, 160.3, 133.6, 133.6, 131.0, 130.9, 115.8, 115.6, 32.4. o-Chlorophenylethylammonium Iodide (o-ClPEAI). Yield 86%. Bright yellow solids.1H NMR (400 MHz, DMSO-d6): δ 7.85 (s, 3H), 7.46 (d, J = 7.6 Hz, 1H), 7.39 (d, J = 6.9 Hz, 1H), 7.38 – 7.27 (m, 2H), 3.01 (td, J = 12.9, 8.6 Hz, 4H);13C NMR (100 MHz, CDCl3): δ 134.6, 133.0, 131.0, 129.4, 128.9, 127.6, 38.3, 30.7;  HRMS (ESI; Figure S43, Supporting Information) m / z: [M + H]+calcd. for C8H11ClIN, 156.0580; found, 156.0585. m-Chlorophenylethylammonium Iodide (m-ClPEAI). Yield 87%. Yellow crystalline solids.1H NMR (400 MHz, DMSO-d6): δ 7.77 (s, 3H), 7.43 – 7.33 (m, 2H), 7.31 (d, J = 8.1 Hz, 1H), 7.24 (d, J = 7.3 Hz, 1H), 3.18 – 3.00 (m, 2H), 2.94 – 2.79 (m, 2H);13C NMR (100 MHz, CDCl3): δ 139.7, 133.1, 130.4, 128.6, 127.5, 126.8, 39.5, 32.5; HRMS (ESI; Figure S44, Supporting Information) m / z: [M + H]+calcd. for C8H11ClIN, 156.0580; found, 156.0567. p-Chlorophenylethylammonium Iodide (p-ClPEAI). Yield 86. Brown solids.1H NMR (400 MHz, DMSO-d6): δ 7.75 (s, 3H), 7.39 (d, J = 8.3 Hz, 2H), 7.30 (d, J = 8.4 Hz, 2H), 3.21 – 2.88 (m, 2H), 3.01 – 2.73 (m, 2H);13C NMR (100 MHz, CDCl3): δ 136.2, 131.4, 130.6, 128.5, 32.2. o-Bromophenylethylammonium Iodide (o-BrPEAI). Yield 90%. Brown solids.1H NMR (400 MHz, DMSO-d6): δ 7.86 (s, 3H), 7.63 (d, J = 8.0 Hz, 1H), 7.38 (d, J = 4.1 Hz, 2H), 7.27 – 7.18 (m, 1H), 3.12 – 2.94 (m, 4H);13C NMR (100 MHz, DMSO-d6): δ 136.3, 132.7, 131.0, 129.1, 128.2, 123.8, 38.4, 33.2. m-Bromophenylethylammonium Iodide (m-BrPEAI). Yield 88%. Yellowish crystalline solid.1H NMR (400 MHz, DMSO-d6): δ 7.76 (s, 3H), 7.51 (s, 1H), 7.46 (d, J = 6.8 Hz, 1H), 7.30 (d, J = 6.9 Hz, 2H), 3.17 – 2.99 (m, 2H), 2.86 (t, J = 7.7 Hz, 2H);13C NMR (100 MHz, CDCl3): δ 140.0, 131.5, 130.7, 129.7, 127.9, 121.8, 39.6, 32.4; HRMS (ESI; Figure S45, Supporting Information) m / z: [M + H]+calcd. for C8H11BrIN, 200.0075; found, 200.0075. p-Bromophenylethylammonium Iodide (p-BrPEAI). Yield 84%. Yellow solids.1H NMR (400 MHz, DMSO-d6): δ 7.75 (s, 3H), 7.53 (d, J = 8.3 Hz, 2H), 7.24 (d, J = 8.3 Hz, 2H), 3.14 – 2.93 (m, 2H), 2.91 – 2.76 (m, 2H);13C NMR (100 MHz, CDCl3): δ 136.6, 131.4, 131.0, 119.9, 32.3. 19   The perovskite solar cells with and without 2D layers were fabricated and characterized under 1 sun illumination. Remarkable improvements in VOCand FF were observed in salt-treated 3D perovskite films indicating superior surface passivation and enhanced hole extraction, respectively, as shown in Figure 15a and Figure 15b. The increase in the JSC for salt-treated films (Figure 15c) is likely to be related to the enhanced VOCand FF resulting in enhanced PCE (Figure 15d), and absorption in 3D perovskite does not increase by the very thin 2D films.2D passivated films show lower hysteresis than the reference film, specifying the reduced ion migration and enhanced charge extraction. The reference 3D device showed the highest PCE of 20.80%, with an open circuit voltage (VOC) of 1.09 V, a short-circuit current (JSC) of 24.54 mA / cm2, and a fill factor (FF) of 79.7%. The device performance is improved significantly by introducing 2D layers on top of 3D perovskite film. The average VOCfor the 3D / 2D PSC is around 1.13 V which implies that the formation of 2D layers by x-RPEAI salts effectively passivates the recombination centers. Better device parameters are observed by inserting the m-RPEAI 2D layer (PCE of >23%), consistent with PL and TRPL studies. The integrated JSCfrom the external quantum efficiency (EQE) measurements aligns with the JSCfrom the current density- voltage (J-V) curve in Figure 15e,f. The optical properties of the reference film and x-RPEAI-treated perovskite films were investigated by PL, TRPL, and ultraviolet-visible absorption (UV-Vis) spectroscopy (Figure 16a-c). PL measurements were done using a 450 nm excitation from the film side. The higher PL intensity of the 2D treated 3D films, located at 812 nm, was observed compared with the reference film, which is commonly associated with decreased nonradiative recombination. There is no PL emission at shorter wavelengths resulting from 2D perovskite due to the low concentration of 2D precursor solutions; thus, highly thin films are produced in the process (Figure 16a). In correlation, the PL spectra of all the salt-treated films among which the -meta positions have the enhanced PL intensity for all halogen substituents. This demonstrates that suppression of nonradiative carrier recombination is superior in - meta halogen substituted RPEAI derivatives. The average carrier lifetime in the 3D / 2D perovskites film is significantly longer compared to the reference device, as shown in Figure 16b. It is envisioned that 2D perovskite films reduce defect density, thereby decreasing nonradiative recombination. All the halogenated 2D salts have longer carrier lifetimes than the reference film, confirming the suppressed nonradiative recombination and enhanced defect passivation, thereby increasing VOC.Among these 9 salts, meta-halogenated derivatives show longer lifetimes than their -ortho and -para counterparts. According to transmission spectra, inserting a 2D layer on top of 3D perovskite does not affect the transmittance of the 3D / 2D hybrid structure (Figure 16c). As conclusion, strong electron donating groups with the ability to coordinate either idodine or lead centers in perovskite, such as -OMe, the preferred substitution position for enhanced performance and stability is the ortho position. 20   Halogens, with less tendecy to form such interaction as mentioned above, is best suited for substitution at the meta position, due to enhanced and correctly oriented dipoles resulted in the 2D perovskite. 21

Claims

CLAIMS 1. Perovskite solar cell comprising 2D passivation layer using compound of 2. R R NH3X where;R is halogen or aromatic group or group, group, thiol or amine or hydrogen X is iodide, bromide or chloride, acetate, triflate, nitrate, alkylsulfate, alkylphosphate, amino acid, tetracyanoborate, dicyanamide, tricyanomethanide, carboxylate, hexaflorophospate, tetrafloroborate, tetrafloromethylacetate or bis(trifloromethanesulfony) imide. With the exception that all Rs are hydrogen.

3. Perovskite solar cell according to claim 1 characterized in that the compound is ortho- methoxy phenylethylammonium iodide.

4. Perovskite solar cell according to claim 1 characterized in that the compound is meta- methoxy phenylethylammonium iodide.

5. Perovskite solar cell according to claim 1 characterized in that the compound is para- methoxy phenylethylammonium iodide.

6. Perovskite solar cell according to claim 1 characterized in that the compound is one of below structure7. Perovskite solar cell according to claim 1 characterized in that the compound is one of below structure  8. Perovskite solar cell according to claim 1 characterized in that the compound is one of below structure 9. Perovskitecompound is one of below structure 10.is one of below structure R R XWhere R is not hydrogen.

11. Perovskite solar cell according to claim 1 characterized in that the compound is o, m, or p-halogen-substituted phenylethylammonium iodide where R is Cl, Br or F and X is iodide.

12. Perovskite solar cell according to claim 1 characterized in that strong electron donating group substitution position is ortho.

13. Perovskite solar cell according to claim 1 characterized in that halogens, substitution position is meta.

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