Perovskite solar cells with dual site binding ligands

Abstract

Perovskite solar cells are provided that comprise a hole transport layer; an electron transport layer; and a perovskite layer between the hole transport layer and the electron transport layer, the perovskite layer comprising a perovskite and perovskite binding ligands, wherein the perovskite binding ligands each comprise an aryl group, a first perovskite binding group bound to the aryl group and bound to a first uncoordinated ion of the perovskite, a second perovskite binding group bound to the aryl group and bound to a second uncoordinated ion of the perovskite, wherein the perovskite binding ligands have a planar orientation relative to a surface of the perovskite between the first and second uncoordinated ions.

Description

PEROVSKITE SOLAR CELLS WITH DUAL SITE BINDING LIGANDSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Patent Application No. 63 / 567.508 that was filed March 20. 2024, the entire contents of which are incorporated herein by reference.REFERENCE TO GOVERNMENT RIGHTS

[0002] This invention was made with government support under 70NANB19H005 awarded by the National Institute of Standards and Technology. The government has certain rights in the invention.BACKGROUND

[0003] The certified power conversion efficiency (PCE) of perovskite solar cells (PSCs) has reached an impressive 25.7%. (J. Park, et al., Nature 616, 724-730 (2023).) Nevertheless, the most efficient PSCs, fabricated in the nip architecture, have yet to achieve the needed operating stability under accelerated aging tests. Inverted (pin) perovskite solar cells, which do not rely on p-type dopants in their hole-transporting layers, have seen progress, but, until now, still lag behind their nip counterparts: their stabilized PCE has so far reached only 25.1%. (C. Liu, et al., Science 382, 810-815 (2023).)SUMMARY

[0004] The present disclosure provides perovskite solar cells comprising perovskite binding ligands. The perovskite binding ligands are capable of binding to uncoordinated ions at surfaces and grain boundaries of a perovskite layer of the perovskite solar cell in a planar orientation. This inhibits nonradiative recombination of charge carriers, including at an interface formed between the perovskite layer and an electron transport layer of the perovskite solar cell, thereby improving power conversion efficiency (PCE). As described in the Example, below, an illustrative perovskite binding ligand. 4-chlorobenzenesulfonate (4C1- BZS), was used in an inverted (pin) perovskite solar cell to achieve a remarkable improvement in PCE, i.e., 26.15% for a 0.05 cm2illuminated area and 24.74% for a 1.04 cm2illuminated area of the solar cell, the record efficiencies for small and large area PSCs. This is nearly 10% higher than a comparative solar cell that does not include 4C1-BZS. Moreover.the pin perovskite solar cell using 4C1-BZS retained 95% of its initial PCE following 1200 hours of continuous 1 sun MPP operation at 65%.

[0005] In one aspect, a perovskite solar cell is provided that comprises a hole transport layer; an electron transport layer; and a perovskite layer between the hole transport layer and the electron transport layer, the perovskite layer comprising a perovskite and perovskite binding ligands, wherein the perovskite binding ligands each comprise an aryl group, a first perovskite binding group bound to the aryl group and bound to a first uncoordinated ion of the perovskite, a second perovskite binding group bound to the aryl group and bound to a second uncoordinated ion of the perovskite, wherein the perovskite binding ligands have a planar orientation relative to a surface of the perovskite between the first and second uncoordinated ions.

[0006] Other principal features and advantages of the disclosure will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Illustrative embodiments of the disclosure will hereafter be described with reference to the accompanying drawings.

[0008] FIGS. 1A-1E. DFT studies of ligand binding and predicted orientation. (FIG. 1A) Structure and electrostatic potential of BZS, 4CH?-BZS and 4C1-BZS ligands. (FIG. IB) Atomic structures of ligands adsorbed in a perpendicular orientation (Conf-perp) on the perovskite surface. (FIG. 1C) Atomic structures of ligand adsorbed in a planar / parallel orientation (Conf-para) on the perovskite surface. (FIG. ID) Formation energy difference between parallel and perpendicular ligand-surface orientations (Ec -para-Econf-perp). (FIG. IE) The adsorption energies (Eads) of Ceo with different molecules (BZS, 4CH3-BZS and 40- BZS) adsorbed perovskite surface. (FIG. IF) Atomic structure of 4C1-BZS ligand shown again along side a schematic illustrating the planar / parallel orientation of the ligand relative to the underlying perovskite surface.

[0009] FIGS. 2A-2F. Surface coordination and passivation of perovskite films. (FIG. 2A) Pb 4f XPS spectra of control and treated perovskite surfaces. (FIG. 2B) Cl 2p XPS spectra of pure 4C1-BZS film, compared with perovskite treated with 4C1-BZS. (FIG. 2C) PLQY of neat control and treated perovskite films on quartz substrates and PLQY results for full devicestacks (FTO / SAM / Perovskite / Ceo) with and without treatment. (FIG. 2D) TRPL lifetimes of neat control and treated perovskite films. The lifetimes for each trace were calculated using a biexponential decay model (data not shown). (FIG. 2E) Differential carrier lifetimes extracted from TRPL spectrum. (FIG. 2F) TPC measurements of control and treated devices.

[0010] FIGS. 3A-3G. PV Performance and stability of inverted solar cells (FIG. 3A) Schematic diagram of device structure. (FIG. 3B) PCE statistics for 30 control and 4C1-BZS treated devices. (FIG. 3C) J-V curves of 4Cl-BZS-treated device with bimolecular passivation. (FIG. 3D) Newport-certified QSS J-V curve of champion 0.05 cm2device. (FIG. 3E) Newport-certified QSS J-V curve of champion 1.04 cm2device. (FIG. 3F) Summary of published nip and pin PSC performance in recent years. (FIG. 3G) ISOS-D-2I device stability during storage at 85 °C for 1500 hours. (FIG. 3H) MPP stability tracking of encapsulated control and 4C1-BZS treated devices under simulated 1 sun illumination at 50% relative humidity and a heatsink temperature of 65 °C. The 4C1-BZS treated device retains 95% of initial efficiency after 1200 hours of operation.DETAILED DESCRIPTION

[0011] Perovskite solar cells are provided which comprise a hole transport layer, an electron transport layer, and a perovskite layer between the hole transport layer and the electron transport layer. The perovskite layer comprises (or consists of) a perovskite, perovskite binding ligands bound to the perovskite, and optionally, an additive. Each of these components of the perovskite solar cells, as well as additional components that may be used, are described in further detail below .

[0012] The perovskite of the perovskite layer refers to a chemical compound having a perovskite structure such as ABXs. In embodiments, A is a protonated amine or an alkali metal ion; B is a divalent metal ion; and X is an anion capable of bonding to B. A variety of protonated amines may be used, e.g., a primary ammonium, a secondary ammonium, a tertiary ammonium, a quaternary ammonium, or an iminium. Suitable illustrative protonated amines include, e.g., NH i (ammonium); CH3NH3 (methylammonium); CH(NH2)2+(formamidinium); (CFE^NFL4(dimethylammonium); (CH3CH2)NH3+(ethylammonium); (NH2)3C+(guanidinium); and (CHs)4N+(tetramethylammonium). A variety of alkali metal ions may be used, e.g.. Cs+. A variety of divalent metal ions may be used, e.g.. a posttransition metal or a metalloid such as Ge2+, Sn2+, or Pb2+. A variety of anions may be used, e.g., a halide such as F’, Cl', Br, or I'.

[0013] The term “perovskite” (as well as the formula ABX3) encompasses alloys including more than one type of A in varying relative amounts (provided the sum of the amounts is about 1); more than one type of B in varying relative amounts (provided the sum of the amounts is about 1); more than one type of X in varying relative amounts (provided the sum of the amounts is about 3); and combinations thereof.

[0014] In embodiments, the perovskite has formula ABX3, wherein A is selected from methyl ammonium, formamidinium, Cs+, and a combination thereof; B is selected from Sn2+, Pb2+, and both; and X is selected from Br\ I , and both. Illustrative such perovskites are provided in the Example, below.

[0015] The perovskite binding ligand is a chemical compound capable of binding to more than one (e.g., two) uncoordinated ion (e.g., B, the divalent metal ion) in the perovskite of the perovskite layer in a planar orientation relative to the perovskite layer. This includes a single perovskite binding ligand that can bind to two B divalent metal ions (e.g., two Pb2+) in the perovskite at the same time. As described in the Example, below, X-ray spectroscopy (XPS) and NMR spectroscopy may be used to confirm bonding (e.g., coordinative bonding) between the perovskite binding ligand and the perovskite. Regarding the planar orientation, this refers to the perovskite binding ligand being aligned parallel with (rather than perpendicular to) a plane defined by a surface of the perovskite to which the perovskite binding ligand is bound. As described in the Example, below, density functional theory (DFT) calculations may be used to confirm that binding of the perovskite binding ligand in the planar orientation is energetically more favorable than in the perpendicular orientation. Coordinative bonding and planar orientation is further described below with respect to an illustrative perovskite binding ligand.

[0016] A suitable perovskite binding ligand comprises (or consists of) an aryl group and more than one (e.g., two) perovskite binding group covalently bound to the aryl group. The exact chemical composition of the perovskite binding ligand, including the aryl group and the perovskite binding groups, depends upon the selected perovskite. Aryl group refers to a monocyclic aryl group having one aromatic ring or a polycyclic group having more than one aromatic ring (e.g.. two, three, etc. rings). Regarding polycyclic groups, neighboring aromatic rings may be fused or unfused. An illustrative aryl group is phenyl. Illustrative perovskite binding groups include oxy gen-containing groups such as a phosphonate group (-PO32) and a sulfonate group (-SO3 ). (It is to be understood that “phosphonate” and “sulfonate”encompass the protonated versions of these groups, e.g., phosphonic acid and sulfonic acid.) Other electron donating groups may be used as perovskite binding groups, such as a halogen (-F, -Cl, -Br, or -I). In the illustrative perovskite binding groups, therepresents the covalent bond to the aryl group. This includes being a direct covalent bond, i.e., to a carbon atom of the aryl group. In embodiments, the perovskite binding ligand includes at least two different types of perovskite binding groups. In embodiments, the perovskite binding ligand includes a sulfonate group and a halogen. In embodiments, the perovskite binding ligand includes at least two perovskite binding groups that are a para position on the aryl group. In embodiments, the perovskite binding ligands are selected from those having a formula (PisG-Ar-PnG'). wherein PBG and PBG’ are different types of perovskite binding groups. Illustrative perovskite binding ligands are provided in the Example, below, and include 4-chlorobenzenesulfonate, 4-fluorobenzenesulfonate, and 4-iodobenzenesulfonate.

[0017] As noted above, the perovskite binding ligands may be bound to the perovskite via coordinative bonding. As shown in FIG. 2A, coordinative bonding may be evidenced by a shift in the position of an XPS peak associated with a divalent metal ion B (here the Pb 4 / XPS peak) of the perovskite to a lower binding energy' relative to the position of the XPS peak in the perovskite but free of the perovskite binding ligand. Similarly, as shown in FIG. 2B, coordinative bonding may be evidenced by a shift in the position of an XPS associated with a perovskite binding group (here, the Cl 2p XPS peak) of the perovskite binding ligand to a higher binding energy relative to the position of the XPS peak in a sample of the pure perovskite binding ligand.

[0018] As also noted above, the perovskite binding ligands bind to the perovskite in a planar orientation. This is illustrated in FIG. IF using an illustrative perovskite binding ligand, 4-chlorobenzensulfonate. The aryl group (phenyl) of 4-chlorobenzensulfonate defines a first plane. The surface of the perovskite between the two uncoordinated ions to which the perovskite binding groups (-SCh" and -Cl) are bound defines a second plane. In the planar orientation (Conf-para), these two planes are oriented approximately parallel to one another such that they do not intersect. By contrast, in the perpendicular orientation (Conf-perp), these two planes are oriented approximately perpendicular to one another such that they do intersect. As also noted above, for the present perovskite binding ligands, the planar orientation is energetically favored, i.e., E(Conf-para) - E(Conf-perp) < 0. (See FIG. ID.) These formation energy values may be determined using DFT calculations as described in the Example, below.

[0019] A single type of perovskite binding ligand or multiple, different types of perovskite binding ligands may be used in the perovskite solar cells.

[0020] The present perovskite binding ligands are distinguished from ligands used in existing approaches. This includes the present perovskite binding ligands having different ty pes of perovskite binding groups therein (i.e., as opposed to the same type). This further includes all the perovskite binding groups in the present perovskite binding ligands being electronegative (e.g., halogen) and / or anionic (e.g., sulfonate, phosphonate). This is as opposed to being electropositive and / or cationic. In addition, the present perovskite binding ligands are not zwitterionic.

[0021] Various amounts of the perovskite binding ligands may be used, including to achieve a desired power conversion efficiency (PCE), e.g., a maximum PCE, for the perovskite solar cell. Illustrative amounts are provided in the Example, below.

[0022] As described in the Example below, in the present perovskite solar cells, the perovskite binding ligands may be localized to surfaces of the perovskite layer and / or grain boundaries therein. This includes being localized at surfaces of the perovskite layer that are in contact with, or form an interface with, other material layers of the perovskite solar cell, e.g., the electron transport layer. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray diffraction (XR.D) may be used to determine the location of the perovskite binding ligands at surfaces and / or grain boundaries versus incorporation within the lattice of the perovskite.

[0023] Additives may be included in the perovskite layer., e.g., to improve the quality of the perovskite layer. Illustrative additives are provided in the Example, below, and include Pbh, and MAPbCh.

[0024] Various materials may be used in the hole transport layer (e.g., carbazole-based self-assembled monolayers (SAMs), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)) and the electron transport layer (e.g., buckminsterfullerene, Ceo, and its derivatives). Any other material layers typically used in perovskite solar cells may be included, e.g., a substate (e.g.. glass, indium tin oxide, fluorine-doped tin oxide), contacts (e.g., various metals), a hole blocking layer (e.g., bathocuproine), an electron blocking layer, a passivating layer (e.g., propane- 1,3-diammonium iodide, 3-(methylthio)propylamine hydroiodide), etc. Additional information regarding the passivating layer may be found in Liu, Cheng, et al. "Bimolecularly passivated interface enables efficient and stable invertedperovskite solar cells." Science 382.6672 (2023): 810-815, which is hereby incorporated by reference in its entirety.

[0025] The present perovskite solar cells may be configured according to a particular architecture such as an inverted (pin) architecture in which the perovskite solar cell is illuminated through the electron transport layer. The perovskite solar cell may be a single junction or a multijunction device (e.g., a tandem device).

[0026] An illustrative inverted perovskite solar cell is shown in FIG. 3A. Fabrication and testing of this perovskite solar cell and other illustrative perovskite solar cells are described in the Example, below.

[0027] The present perovskite solar cells are characterized by high pow er conversion efficiencies (PCEs) which may be tested as described in the Example, below. In fact, the illustrative inverted perovskite solar cell of FIG. 3A achieved a certified quasi-steady state PCE of 26. 15% for a 0.05 cm2illuminated area. (See FIG. 3D.) To the inventors’ knowledge, this is believed to be a world record for a perovskite solar cell. (See FIG. 3F.) As shown in FIG. 3B, this improvement is believed to be due to the use of the present perovskite binding ligands, which enable substantially higher PCEs as compared to other types of ligands (benzenesulfonate, BZS and p-toluenesulfonate, 4CH3-BZS) and as compared to a perovskite solar cell free of any such ligands (Control).

[0028] Various methods may be used to fabricate the present perovskite solar cells. However, in embodiments, the perovskite layer is provided by depositing (e.g., via spin coating) a perovskite precursor solution comprising (or consisting ol) the perovskite, the perovskite binding ligands, a solvent, and optionally, the additive, followed by annealing. The amount of the perovskite binding ligands in the perovskite precursor solution may be adjusted to achieve a desired PCE as noted above. Additional illustrative details regarding deposition of the perovskite layer as well as the other material layers of the perovskite solar cells are provided in the Example, below.

[0029] Methods of using the present perovskite solar cells are also provided. The methods comprise illuminating any of the disclosed perovskite solar cells with light, e.g., through the electron transport layer, to generate charge carriers, and collecting the charge earners.EXAMPLE

[0030] This Example describes fabrication of pin perovskite solar cells incorporating ligands that bind two neighboring Pb2+defect sites in a planar ligand orientation on the perovskite. This Example reports a certified quasi-steady state PCE of 26. 15% and 24.74% for 0.05 and 1.04 square centimeter illuminated areas, respectively. The devices retained 95% of their initial PCE following 1200 hours of continuous 1 sun MPP operation at 65 °C.

[0031] Materials and Methods

[0032] Materials

[0033] [2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid (2PACz), [4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl]phosphonic Acid (Me-4PACz), Pbh (99.99%) and PbCh were purchased from TCI Chemicals. CsI (99.99%), Sodium benzenesulfonate (BZS), Sodium p- toluenesulfonate (4CEh- BZS), Sodium 4-chlorobenzenesulfonate (4C1-BZS), 4- fluorobenzenesulfonic acid (4F-BZSA) and 4-Iodobenzenesulfonic acid (4I-BZSA) were purchased from Sigma-Aldrich. Formamidinium iodide (FAI), methylammonium iodide (MAI), and methylammonium chloride (MAC1) were purchased from Greatcell Solar Materials. N, N-dimethylformamide (DMF, anhydrous, 99.8%), dimethyl sulfoxide (DMSO, anhydrous, 99.9%), isopropanol (anhydrous, 99.5%), ethanol (anhydrous, 99.5%), and anisole (anhydrous, 99.7%) were purchased from the Millipore Sigma. Cgo. bathocuproine (BCP), and 1,3-propane diammonium iodide (PDAE) were purchased from Xi’an Yuri Solar Co., Ltd. All the materials were used as received without any purification. 3 -(methylthio) propylamine hydroiodide (3MTPAI) was obtained by the reaction of hydroiodic acid and 3MTPA (Sigma-Aldrich, 97%) with molar ratios of 1 : 1. Hydroiodic acid was slowly added to amines under stirring in the ice water bath. The solution was stirred in the ice water for 2 hours, followed by rotary evaporation at 50 °C until the white solid w as obtained, which w as washed with diethyl ether several times. Finally, the product was dried in a vacuum dry ing oven to obtain the corresponding ammonium halide salts.

[0034] Perovskite precursor solutions

[0035] Normal bandgap perovskite. 1.67 M CsoosMAo.iFAo.ssPbh perovskite precursors were prepared by dissolving 0.075 mmol CsI, 0.15 mmol MAI, 1.275 mmol FAI, and 1.5 mmol PbE in 0.9 mL mixed DMF and DMSO solution (745 pL DMF + 155 pL DMSO). 15 mg MAC1 and 35 mg Pbh were added to improve the quality of perovskite films,and these may have contributed positively to the anchoring of additives by providing adequate Pb2+sites. The precursor solutions were stirred at 60 °C for 1 h and then filtered using a 0.22 polytetrafluoroethylene membrane before use. In studies comparing different additives, a 1 mg ml’1concentration was used for all additives to determine which additive provided the greatest improvement (4C1-BZS). The concentration of 4C1-BZS was then optimized, testing 0.5, 1. and 2 mg ml'1, and it was found that 1 mg ml’1is the best concentration for 4C1-BZS.

[0036] Wide bandgap (WBG) perovskite. A 1.2 M wide-band gap perovskite precursor solution with a composition of FAo.sCso.2Pb(Io.6Bro.3s)3 with 5% mol MAPbCh additive was prepared by dissolving CsI, FAI, PbBr2, Pbh MAC1, and PbCh in mixed solvents of DMF and DMSO with a volume ratio of 4: 1. 0.5 mg 4C1-BZS chemical was added into 1 mL WBG precursor for 4Cl-BZS-treated WBG device fabrication. The precursor solution was stirred at 60 °C for 1 h and then filtered using a 0.22 pm PTFE membrane before use.

[0037] Narrow bandgap (NBG) perovskite. A 1.8 M narrow-bandgap perovskite precursor solution with a composition of Cso.o5FAo.7MAo.25Pbo.5Sno 5I3 was prepared by dissolving CsI, FAI, MAI, Snh and Pbh in the mixed solvents of DMF and DMSO with a volume ratio of 3: 1. Tin powders (5 mg), GuaSCN (4 mg), SnF2 (14 mg), 4F-PEABr (2 mg), and glycine hydrochloride (4 mg) were added to the precursor solution. 1 mg 4C1-BZS chemical was added into 1 mL NBG precursor for 4Cl-BZS-treated NBG device fabrication. The precursor solution was then stirred at room temperature for 1 h. The precursor solution was filtered using a 0.22 pm Polytetrafluoroethylene (PTFE) membrane before using.

[0038] Solar cell fabrication

[0039] Single-junction normal bandgap device. Prepattemed Fluorine-doped tin oxide (FTO) glasses were cleaned using acetone and isopropanol for 20 min each in an ultrasonic bath, followed by ultraviolet ozone treatment for 30 min. The hole transport layer (HTL) was fabricated by using the mixed SAM solution of 2PACz and Me-4PACz in a glovebox. The 2PACz concentration was 0.17 mg ml’1and Me-4PACz concentration was 0.33 mg ml’1. The SAM in ethanol solution was spin-coated on FTO at 3,000 r.p.m. for 30 s, followed by annealing at 120 °C for 10 min. The perovskite solutions were spin-coated at 1000 r.p.m for 10 s (acceleration rate 500 r.p.m. / s) and 5000 r.p.m. for 35 s (acceleration rate 1000 r.p.m. / s), respectively. At the last 15 s of the second step, 150 pL anisole was dropped as the antisolvent. The films were then annealed at 120 °C for 10 min.

[0040] For the bimolecular passivation (BMP) treatment, 12 mM 3MTPAI and 6 mM PDAI2 were dissolved in a 1 mL isopropanol / chlorobenzene (1: 1 v / v) solvent and filtered before use. A 120 pL mixed solution was spin-coated on the perovskite films at 4000 r.p.m for 25 s, followed by annealing at 100 °C for 5 min. After cooling dow n to room temperature, the substrates were transferred to the evaporation system and a 25 nm Ceo film was subsequently deposited on top by thermal evaporation at a rate of 0.2 A s \ After finishing the Ceo deposition, the substrates were then transferred to the atomic layer deposition (ALD) system (Picosun) to deposit 20 nm SnCh at 90 °C using precursors oftetrakis(dimethylamino) tin (iv) (99.9999%) and deionized water. Finally, a 140 nm Ag electrode w as evaporated by thermal evaporation.

[0041] Single junction wide bandgap perovskite solar cells. NiO. nanocrystal (5 mg mF1in H2O and 2-Propanol mixed solvent with volume ratio of 3 : 1) layers were first spin- coated on ITO substrates at 3,000 rpm for 25 s in air without any post-treatment, then the substrates w ere immediately transferred to the glovebox. The NiOxnanoparticles were prepared via the hydrolysis reaction of nickel nitrate. Me-4PACz (0.5 mg mF1) in ethanol was spin-coated on the NiCF film at 3.000 rpm for 25 s and then annealed at 100 °C for 10 min. For the perovskite film fabrication, the substrate was spun at 4000 rpm for 32 s with an acceleration of 1000 rpm, and 100 pL Anisole w as dropped onto the substrate during the last 8 s of the spinning. The substrates were then transferred onto a hotplate and heated at 100 °C for 15 min. For the electron transport layer (ETL), 25 nm Ceo was thermally evaporated on tire perovskite films at a rate of 0.2 A s ' under a high vacuum of ~10-7Torr, followed by 7 nm BCP evaporation as a hole-blocking layer. Finally, a 140 nm Ag electrode was evaporated by thermal evaporation.

[0042] Single junction Pb-Sn perovskite solar cells. PEDOT: PSS w as spin-coated on ITO substrates at 6,000 rpm for 30 s and annealed on a hotplate at 160 °C for 20 min in ambient air. After cooling, the substrates were transferred immediately to a nitrogen-filled glovebox for the deposition of perovskite films. The perovskite films were deposited with a two-step spin-coating procedure: (1) 1,000 rpm for 10 s with an acceleration of 200 rpm s’1, and (2) 3800 rpm for 45 s with an acceleration of 1000 rpm s’1. 300 pl chlorobenzene (CB) was dropped onto the spinning substrate during the second spin-coating step at 20 s before the end of the procedure. The substrates were then treated on a hotplate for 10 min at 100 °C. 25 nm Ceo, 7 nm BCP, and 140 nm Ag were sequentially deposited on top of the perovskite layer by thermal evaporation.

[0043] Device testing. The current density -voltage (J-V) characteristics were measured using a Keithley 2400 source meter under illumination from a solar simulator (Newport, Class A) with a light intensity of 100 S5 Mw cm'2(checked with a calibrated reference solar cell from Newport). The J-V curves were measured in a nitrogen atmosphere with a scanning rate of 100 mV s'1(voltage step of 10 mV and delay time of 200 ms). The active area was determined by the aperture shade mask (0.049 cm2for small-area devices, 1.04 cm2for large-area devices) placed in front of the solar cell. A spectral mismatch factor of 1 .0 was used for all J-V measurements. The external quantum efficiency (EQE) was measured in ambient air using the solar-cell-spectra-response measurement system (QE-R, EnliTech).

[0044] Stability testing. Devices were placed in a homemade stability -tracking station. The illumination source was a UV- free white-light LED with its intensity’ calibrated to match 1 sun conditions. The spectrum of the white-light LED simulator used in MPP stability tracking is found in J. Xu, et al., Nat. Mater. 22, 1507-1514 (2023). For the ISOS- L-3 ageing test, the device chamber was left open in a room with 50 ± 10% relative humidity, and the solar cell was mounted on a metal plate kept at 65 °C using a heating element. A thermal couple attached to the metal plate was used to monitor and provide feedback control to the heating element to ensure temperature consistency. For thermal stability tests, the encapsulated cells were heated at 85 °C in nitrogen. The device performance was evaluated periodically. Encapsulation was performed using a capping glass slide, with ultraviolet-adhesive (Lumtec LT-U001) as a sealant.

[0045] Crystallographic characterizations. The X-ray diffraction (XRD) spectra were measured on a Bruker D8 Advance X-ray diffractometer at room temperature using Cu- K< / . radiation (A = 1.54178 A) at 40 kV and 40 mA. Grazing-incidence wide-angle A-ray Scattering (GIWAXS) was conducted on perovskite films at the Brockhouse X-ray Diffraction and Scattering Sector Low Energy Wiggler (BXDS-WLE) beamline of the Canadian Light Source (CLS) using a photon energy of 15. 12 keV (A = 0.82 A). A Rayonix MX300 detector 328.04 mm away from the sample was used for collecting patterns.

[0046] Other characterizations. NMR spectra were recorded by Bruker Avance III HD500. Time of flight secondary’ ion mass spectrometry’ (ToF-SIMS) was collected by a IONTOF M6 instrument using a primary’ 30 keV Bi ion source with an analysis area of 50 x50 pm2. SEM images were collected by aJEOL JSM-7900FLV microscope using a 5 keV and 10 keV electron beam for surface and cross-section images, respectively. Time-resolved photoluminescence (TRPL) measurements were carried out using a Horiba Fluorolog time- correlated single photon counting system with photomultiplier tube detectors. A pulsed laser diode (634 nm, 110-140 ps pulse width) was used as the excitation source for steadystate and transient measurements. The luminescence quantum yield was measured by a LuQY Pro System (Quantum Yield Berlin) under the excitation of a 532 nm laser (100 mW). Y-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were performed on Thermo Scientific ESCALAB 250Xi with an A-ray spot size of 500 pm. The XPS instrument was calibrated using silver metal, with the Ag 3d5 / 2 peak set at 368.2 eV. The sampling depth was 10 nm. and the spectrum remained unaffected by the underlying substrate. Throughout the XPS analysis, a low-energy electron gun was employed to flood the analysis area, neutralizing surface charges. In the post-processing phase, the adventitious carbon peak was standardized at 284.8 eV to calibrate all spectra and mitigate surface charging effects. An XPS optical microscope was utilized, and particle aggregation was observed on the substrate. The X-ray spot, with a diameter of 400 pm, was precisely focused on an aggregated region with a thickness of several micrometers. The influence of the underlying substrate should be omitted from the analysis. Each sample was connected to the grounded sample holder using copper conductive tape. Additionally, charge compensation was performed prior to each measurement. Transient photocunent (TPC) was conducted by the Fluxim Paios system. Kelvin probe force microscopy (KPFM) images were generated using an Asylum Cypher S atomic force microscope (Oxford Instruments) with a Ti-Ir-coated ASYELEC.01-R2 cantilever and k= 4 ± 0.5 N m1(Asylum Research). Scans were performed over 2 pm at 512 pixels and 0.5 Hz in a two-pass nap method, the first pass in tapping mode and the second in KPFM mode with a tip potential of 5 V and surface clearance of 5 nm.

[0047] NMR analysis. It was found that Ci connecting the SO+ unit showed the largest chemical shift (data not show n). This was attributed to electron- withdrawal from the substituent. Cr. located at the para position, showed the second largest chemical shift, which was assigned to the conjugating effect. After the introduction of Pbh, the chemical shift of Cl moved to a higher field (-0.4), which was ascribed to the decrease of the electronwithdrawing capability of the substituent following coordination with PbE. In contrast, the C4 peak shifted to a lower field (+0.22), which was ascribed to the enhancement of theconjugating effect after the coordination of SCty and Pbh. Similar changes were observed for the methyl-substituted molecule (data not shown). The change of the chemical shift is indicative of the strong interaction between SOs' and Pbh

[0048] For the molecule with chlorine substituent CI-BZS-PbL. the change of the chemical shift of Ci and C4 after the interaction with Pbh was reduced (-0.36, +0.1), indicating that the chlorine atom influenced the electron density of the carbon atoms. To study the effect of the chlorine substituent in particular, the NMR spectrum of chlorine benzene was studied. The peak of Ci connecting to the chlorine atom moved to a higher field after the addition of Pbh (-0.09) (data not shown). This can be ascribed to the interaction between chlorine and P b I2 that reduced the electron- withdrawing character. The peak of C4 moved to a lower field due to the enhancement of the conjugating effect (+0.03). These shifts indicate interactions betw een the chlorine and lead. For the molecule with both chlorine and SOs' substituents (data not shown), the movement of the chemical shift w as reduced compared to BZS-Pbh, and the overall movement of the peak position in 4C1- BZS+Pbh was almost consistent with the sums of the shifts observed for single SOs' and Cl substituents. This indicates the interaction of both SOs' and Cl with Pbh.

[0049] First-principles calculations. First-principles calculations based on density functional theory (DFT) were carried out using the Vienna Ab initio Simulation Package (VASP). For the exchange-correlation functional, the Perdew-Burke-Emzerhof functional (PBE) was adopted. The DFT-D3 method was used for the van der Waals (vdW) correction. Dipole corrections were taken into consideration in the work function calculations. The planewave cutoff energy w as 400 eV. The energy and force convergence criteria w ere set to 10'5eV and 0.03 eV- '1, respectively-. The adsorption energies ( / +,ds) of Cgo with different molecules (BZS, 4CHs-BZS and 4C1-BZS) adsorbed perovskite surface were calculated as £(C6o@perovskite)-E(C6o)-.E'(perovskite). The electrostatic potentials ($9) of the passivators were calculated in the Gaussian 09 package at the B3LYP / def2TZVP level with DFT-D3.

[0050] Results and Discussion

[0051] Theoretical Investigation

[0052] Ligands containing a benzene ring w ere selected for evaluation, as its flat structure may lie parallel to an underlying surface. To enable strong binding with perovskitesurfaces, both -PCh2’ and -SO?' functional groups were considered, both of which have a high number of oxygen atoms.

[0053] steric constraints were then evaluated. Desirably, the ligand is sufficiently long that it can bind at multiple surface Pb sites. These were ~ 6.3 A apart in the case of FA-based perovskites. Benzenesulfonate (BZS) ligands and their derivatives had a length of ~ 5.7 A.

[0054] Density functional theory (DFT) calculations were used to investigate how the molecular structure of the ligand affects orientation. Three ligands were considered: one with no additional functional group (BZS), and two with methyl or chloride in the para position of the benzene ring opposite to the sulfonate functional group (4-methylbenzenesulfonate, 4CH?-BZS, and 4-chlorobenzenesulfonate, 4C1-BZS) (FIG. 1 A). 4CH3-BZS and 4C1-BZS have lengths of 6.14 A and 6.37 A, respectively. The formation energies of two configurations were compared: one in which the ligands were oriented perpendicular to the perovskite surface (Conf-perp, FIG. IB), and another in which the ligands adopted a parallel orientation with respect to the perovskite surface (Conf-para, FIG. 1C). Although Conf-perp was more energetically favorable for BZS and 4CH3-BZS, Conf-para was energetically more favorable for 4C1-BZS because of the additional Pb2+surface binding afforded by the Cl functional group (FIG. ID) that would enable dual-site Pb2+passivation. The effects of ligand orientation on charge transfer at the perovskite / ETL interface were also investigated by examining fullerene (Ceo). which is widely used as ETL in pin PSCs and known to induce energetic losses in devices. Analysis of the calculated charge density difference (FIG. IE) provided evidence that 4C1-BZS, when absorbed on the perovskite layer, established a notably stronger binding strength with the Ceo layer (E'ads= -0.85 eV), in contrast to the BZS (Eads= -0.46 eV) and 4CH3-BZS (Eads= -0.39 eV). Fracture energy’ (Gc) results showed that 4C1-BZS increased the mechanical strength of perovskite / Cso interface (data not shown).

[0055] Ligand-Perovskite Binding Characterization

[0056] In order to explore interactions between perovskite and BZS ligands, each ligand was added directly into the precursor solutions and spin-coating Cso osFAo ssMAo iPbb perovskite thin films, where FA is formamidinium and MA is methylamine. Time-of-flight secondary’ ion mass spectrometry’ (ToF-SIMS) of untreated (control) and treated films showed that BZS, 4CH3-BZS, and 4C1-BZS were all concentrated near the top (ETL-facing) surface of the perovskite film (data not shown). This result, combined with X-ray diffraction (XRD) patterns of control and treated perovskite films that showed no discernable peak-shifting after treatment (data not shown), indicated that the ligands did not enter the lattice, but rather diffused toward the top surface during film crystallization. Scanning electron microscopy (SEM) images of perovskite films with additives were obtained, illustrating that the perovskite films (both additives and controls) exhibited substantially uniform morphology (data not shown).

[0057] X-ray photoelectron spectroscopy (XPS) was used to look for evidence of Pb2+coordinative bonding, examining Pb 4 core levels of control versus treated perovskite films. A shift of the Pb 4 / XPS peaks to a lower binding energy was observed for each of the treated films relative to the control, indicative of SCh -Pb coordination bonding (FIG. 2A). To investigate whether the Cl functional group w as responsible for additional Pb coordination, XPS spectra of pure 4C1-BZS film w ere compared with that of 4Cl-BZS-treated perovskite films. The Cl 2p core level shifted to a higher binding energy in the treated perovskite films compared to pure 4C1-BZS film (FIG. 2B), consistent with the donation of electron density- associated with coordination bonding with positively -charged Pb2+. The NMR results (data not shown) indicated Cl-Pb bonding between 4C1-BZS and perovskite.

[0058] Optoelectronic Characterization of Perovskite Films and Device Stacks

[0059] To evaluate the passivation efficacy of each ligand, photoluminescence (PL) of neat control and treated perovskite films was studied. An increase in PL quantum yield (PLQY) was observed for each of the treated films and the full device stack (FIG. 2C), with 4C1-BZS exhibiting a twofold increase in PLQY (41%) compared to control films (20%), which corresponded to a projected 20 mV increase in quasi-Fermi level splitting (QFLS). The PLQY of full-device stacks (FTO / SAMs / perovskite / Ceo, wherein FTO is fluorinated tin oxide and SAMs are mixtures of 2PACz and Me-4PACz) revealed a significant improvement after 4C1-BZS treatment: 5% for 4C1-BZS compared to 0.6% for the control, corresponding to 1.17 V and 1.1 V in QFLS for 4C1-BZS and the control device, respectively. This improvement was consistent with reduced interface losses. Time-resolved photoluminescence (TRPL) revealed a similar increase in carrier lifetimes after treatment. Specifically, 4Cl-BZS-treated films exhibited a weighted-average lifetime of 3.0 ps compared to 0.6 ps for the control film (FIG. 2D).

[0060] Partial and full perovskite / ETL device stacks were fabricated to probe interface recombination and charge transfer. First, TRPL measurements of perovskite / Ceo stacks were conducted, wherein decay w as dictated by non-radiative surface / bulk recombination(monoexponential decay), radiative recombination (second-order decay), and charge extraction effects, which could be distinguished if the time constants for each process differed sufficiently. The first interval at shorter times was dominated by the transfer of electrons from the bulk into the Ceo, and the second interval at longer delay times was dominated by interfacial recombination. The sharp drop in emission for 4Cl-BZS / Ceo indicated efficient electron transfer at the interface, and the longer second-order decay time was indicative of a reduced trap density compared with BZS and 4CH3-BZS (data not shown). This effect of this reduction was especially evident in fits to the TRPL traces to compute the differential lifetime as T = -{d ln[ (t) ] / dt j1(FIG. 2E), where (f) is the time-dependent PL photon flux, as the sharpness of the rise implied the speed of the electron transfer from perovskite to Ceo.

[0061] Transient photocurrent measurements of full device stacks in which mixed self assembled monolayers (SAMs) were used as the HTL (see Methods) revealed a similar trend. Both BZS and 4CH3-BZS resulted in slower photocurrent decay, while 4C1-BZS treatment led to faster photocurrent decay (FIG. 2F). This observation suggested that electron extraction became more efficient. Ultraviolet photoelectron spectroscopy (UPS) revealed an increased conduction band offset with Ceo that was caused by a Fermi-level upshift after BZS and 4CH3-BZS treatment, whereas 4C1-BZS caused a Fermi-level downshift and reduced conduction band offset (data not shown). This trend was further confirmed by Kelvin probe force microscopy (KPFM) measurements (data not shown) and DFT calculations (data not shown).

[0062] Inverted Perovskite Solar Cells

[0063] Using 4Cl-BZS-treated perovskite, inverted PSCs ith the structure FTO / SAM / perovskite / Ceo / SnCh / Ag were fabricated (FIG. 3A). The thickness of the perovskite layer was 900 nm. Control devices had PCE 24%, while the 4C1-BZS treated devices exhibited PCE 26.3% (data not shown). Analysis of device statistics for both control and 4C1-BZS treated PSCs revealed a substantial enhancement in PCE, primarily via increased open-circuit voltage (Foe). Additionally, 4Cl-BZS-treated PSCs show ed a significantly higher FF compared to BZS and 4CH3-BZS-treated PSCs. This improvement in FF was attributed to enhanced charge extraction in 4Cl-BZS-treated PSCs (FIG. 3B data not shown).

[0064] The effectiveness of the additive change with a stronger or weaker donating group, namely 4F-BZS, 4Br-BZS and 4I-BZS, was also evaluated. Notably, 4F-BZSexhibited a more negative averaged electrostatic potential (ESP), whereas 4I-BZS displayed a more positive averaged ESP (data not shown). It was posited that a stronger donating group, such as Cl or F, was beneficial in providing dual-site defect passivation. The structurally similar molecules 4-fluorobenzenesulfonic acid (4F-BZSA) and 4-Iodobenzenesulfonic acid (4I-BZSA) were utilized in the devices. Remarkably, treatments with 4F-BZSA resulted in comparable PCE as in the case of 4C1-BZS, and 4I-BZSA also showed improved PCE compared to controls (data not shown).

[0065] The bimolecular surface passivation (BMP) approach was then added, based on 3MTPAI and PDAh. (See C. Liu et al., Science 382, 810-815 (2023).) This strategy provides a combination of chemical and field-effect passivation. The PLQY of full-device stacks (FTO / SAMs / perovskite / BMP / Cso) indicated a further improvement after the BMP treatment (data not shown). The combined treatment elevated the PCE of 4Cl-BZS-treated devices from 26.3% to 26.9%. featuring a Foe of 1. 18 V, FF of 86.2%. and short-circuit current density (. / sc) of 26.4 mA cm'2(FIG. 3C). Statistics of photovoltaic parameters for devices with bimolecular passivation revealed additional improvements in both Voc and PCE (data not shown).

[0066] The bandgap of the pin PSCs w as taken from external quantum efficiency (EQE) measurements as 1.53 eV (data not shown). Devices with an active area of 0.05 cm2and 1.04 cm2were sent to a NREL-accredited independent PV calibration laboratory (Newport) for certification. The devices achieved a certified stabilized (QSS) PCE of 26.15% and 24.74%, respectively (FIGS. 3D, 3E). These reported pin PSC PCEs surpassed the record nip device performance reported in recent years (FIG. 3E).

[0067] Next, the thermal stability of the 4C1-BZS treated PSCs was tested following protocols established by the International Summit on Organic Photovoltaic Stability (ISOS)- D-2I. in which encapsulated devices were subjected to dark storage at 85 °C and tested periodically. 4CLBZS treated PSCs retained 95% of their initial efficiency after 1500 hours of storage at 85 °C (FIG. 3G). To evaluate operating stability further, ISOS-L-3 testing w as carried out. in which encapsulated devices were subjected to continuous 1-sun equivalent illumination using a UV-free white-LED and held at the maximum power point (MPP) voltage, at 50% relative humidity and a heatsink temperature of 65 °C (FIG. 3H). 4C1-BZS treated PSCs achieved a T95 (the time taken for the device PCE to drop to 95% of the initial value) of 1200 hours after continuous MPP tracking at 65 °C, while control devices droppedfrom an initial efficiency of 22% to 18.7% after 1200 hours (data not shown). Furthermore, 4C1-BZS treated PSCs achieved a Tsi of 540 hours after continuous MPP tracking at 85 °C (data not shown).

[0068] Conclusions

[0069] Based on the inventors’ insight that dense packing of passivator ligands perpendicular to the perovskite / Ceo interface may increase resistance, this Example presents a different approach involving introducing ligands that align in a planar orientation relative to the perovskite surface. The interaction of 4C1-BZS with undercoordinated Pb2+ions reduced the surface defect density’ and minimized the energetic mismatch between the perovskite and Ceo. The study indicates that the approach was surprisingly effective in increasing pin PSC performance, bringing it into the range of that achieved in the nip configuration. The approach retained the benefits of 65 °C 1 sun MPP operating stability' seen in pin PSCs.

[0070] To test whether the approach worked in a range of perovskite compositions, 4C1- BZS-treated 1.78 eV wide-bandgap mixed halide devices were fabricated, as well as 1.25 eV narrow-bandgap mixed Pb-Sn PSCs - compositions of interest in all -perovskite tandem solar cells. In each case, an increase in PCE was observed following 4C1-BZS treatment (data not shown).

[0071] Additional information regarding the Example, including data indicated as being not shown, may be found in U.S. Provisional Patent Application No. 63 / 567,508, filed March 20, 2024, which is incorporated by reference in its entirety'.

[0072] The w ord "illustrative" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "illustrative" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, "a" or "an" means "one or more.”

[0073] The foregoing description of illustrative embodiments of the disclosure has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principles of the disclosure and as practical applications of the disclosure to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as suited to theparticular use contemplated. It is intended that the scope of the disclosure be defined by the claims appended hereto and their equivalents.

[0074] If not already included, all numeric values of parameters in the present disclosure are proceeded by the term “about” which means approximately. This encompasses those variations inherent to the measurement of the relevant parameter as understood by those of ordinary skill in the art. This also encompasses the exact value of the disclosed numeric value and values that round to the disclosed numeric value.

[0075] The term “ty pe” as used herein refers to chemical formula such that a single ty pe means the same chemical formula and different type means different chemical formula. Similarly, use of “more” as in “one or more” and the like refers to use of different types of the relevant entity.

[0076] Terms such as “comprising” and the like may be replaced with terms such as “consisting” and the like.

[0077] In recognition of the inherent nature of chemical synthesis, throughout the present disclosure, terms and phrases such as “absence,” “free,” “does not comprise,” etc. encompass, but do not require a perfect absence of the referenced entity.

Claims

WHAT IS CLAIMED IS:1 . A perovskite solar cell comprising: a hole transport layer; an electron transport layer; and a perovskite layer between the hole transport layer and the electron transport layer, the perovskite layer comprising a perovskite and perovskite binding ligands, wherein the perovskite binding ligands each comprise an aryl group, a first perovskite binding group bound to the ary l group and bound to a first uncoordinated ion of the perovskite, a second perovskite binding group bound to the aryl group and bound to a second uncoordinated ion of the perovskite, wherein the perovskite binding ligands have a planar orientation relative to a surface of the perovskite between the first and second uncoordinated ions.

2. The perovskite solar cell of claim 1, wherein a plane defined by the aryl group is aligned parallel with a plane defined by the surface of the perovskite between the first and second uncoordinated ions.

3. The perovskite solar cell of claim 1, wherein the perovskite binding ligands are characterized by a formation energy in the planar orientation (Econf-para) and a formation energy in a perpendicular orientation (Econf-perp) and Econf-Para “ Econf-perp 0.

4. The perovskite solar cell of claim 1, wherein the first perovskite binding group and the second perovskite binding group are of different types.

5. The perovskite solar cell of claim 1, wherein the ary l group is phenyl.

6. The perovskite solar cell of claim 1, wherein the first and second perovskite binding groups are selected from a phosphonate group, a sulfonate group, and a halogen.

7. The perovskite solar cell of claim 1, wherein one of the first and second perovskite binding groups is a sulfonate group and the other is a halogen.

8. The perovskite solar cell of claim 1, wherein the first and second perovskite binding groups are in a para position on the aryl group.

9. The perovskite solar cell of claim 1, wherein the perovskite binding ligands are selected from those having formula PBG-Ar-PBG’, wherein PBG and PBG’ are of different types.

10. The perovskite solar cell of claim 9, wherein Ar is phenyl.

11. The perovskite solar cell of claim 9, wherein PBG and PBG’ are selected from a phosphonate group, a sulfonate group, and a halogen.

12. The perovskite solar cell of claim 9, wherein the first and second perovskite binding groups are in a para position on the aryl group.

13. The perovskite solar cell of claim 1, wherein the perovskite binding ligands are selected from 4-chlorobenzenesulfonate, 4-fluorobenzenesulfonate, 4-iodobenzenesulfonate, and combinations thereof.

14. The perovskite solar cell of claim 1, wherein the perovskite binding ligands are localized at an interface formed between the perovskite layer and the electron transport layer.

15. The perovskite solar cell of claim 1, wherein the perovskite has formula ABX3, wherein A is a protonated amine or an alkali metal ion; B is a divalent metal ion; and X is an anion bound to B.

16. The perovskite solar cell of claim 15, wherein A is selected from methyl ammonium, formamidinium, Cs+, and a combination thereof; B is selected from Sn2+, Pb2+, and both; and X is selected from Br, I’, and both.

17. The perovskite solar cell of claim 16, wherein the perovskite binding ligands are selected from those having formula PBG- Ar-Pn<;'. wherein PBG and PBG’ are of different types, wherein Ar is phenyl, and wherein PBG and PBG’ are selected from a phosphonate group, a sulfonate group, and a halogen.

18. The perovskite solar cell of claim 17, wherein the perovskite binding ligands are selected from 4-chlorobenzenesulfonate, 4-fluorobenzenesulfonate, 4- iodobenzenesulfonate, and combinations thereof.

19. The perovskite solar cell of claim 1, having an inverted (pin) architecture wherein the perovskite solar cell is illuminated through the electron transport layer.

20. A method of using the perovskite solar cell of claim 1, the method comprising illuminating the perovskite solar cell to generate charge carriers and collecting the charge carriers.

Images