Enhancing stability and efficiency of perovskite solar cells with ionic liquids

Abstract

Ionic liquids and their use in thin films and photovoltaic devices such as perovskite solar cells, are disclosed.

Description

ENHANCING STABILITY AND EFFICIENCY OF PEROVSKITE SOLAR CELLS WITH IONIC LIQUIDSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U. S. Provisional Patent Application No.63 / 715,757, filed November 4, 2024, the entire contents of which are hereby incorporated by reference as if fully set forth.TECHNICAL FIELD

[0002] The present disclosure relates to ionic liquids and their use in enhancing the stability and efficiency of perovskite solar cells.BACKGROUND

[0003] Although single-junction perovskite solar cells (PSCs) have achieved an impressive, certified power conversion efficiency (PCE) of 26.7%, their market commercialization has been hindered by challenges related to scalability and long-term operational stability, which has steered the transition of research focus from efficiency to scalability and stability. Recently, significant progress in scalability has been made through methods such as in situ vapor-solid reaction transformation (10.1002 / adfm.202313435), vacuum deposition( 10.1016 / j.mtener.2024.101506), and rapid drying-induced high-supersaturation states (10.1126 / sciadv.adl6390), which have enabled the formation of high-quality perovskite layers. However, even when environmental stressors, such as water and oxygen, are excluded, the current lifetime of PSCs remains shorter compared to that of silicon solar cells.

[0004] Stability issues can be categorized into two main types: intrinsic and extrinsic.Intrinsic factors include hygroscopicity, strain, and ion migration, while extrinsic factors encompass moisture, oxygen, light exposure, heat, and electric fields. These factors contribute to radiative recombination and non-radiative recombination processes at the bulk perovskite and perovskite / charge carrier layer interfaces, ultimately reducing device efficiency and stability. To address these challenges, several strategies have been developed, including composition engineering, crystallization regulation, interface modification, and improved encapsulation methods Despite these advancements, the reported stability remains significantly below thetargeted -25-year operational lifetime required for commercial viability, as per International Electrotechnical Commission standards. Thus, there remains a need for PSCs with improved stability.

[0005] In view of the foregoing, it is an object of the present disclosure to address this unmet need. This and other objects and advantages, as well as inventive features, will become apparent from the detailed description provided herein.SUMMARY

[0006] Provided is an ionic liquid composition to enhance the stability and efficiency of devices, such as perovskite-containing devices, e.g., perovskite solar cells. The ionic liquid composition can comprise at least one compound having a structure selected from:

[0007] Further provided is a device comprising a perovskite layer and an above-described ionic composition. In embodiments, the ionic composition can compriseMEM-MIMin which X can be Cl. In embodiments, the device can further include (i) an electrode layer; (ii) an electron transport layer operationally connected to and sandwiched between the electrode layer and the perovskite layer; (iii) a transparent oxide layer; and (iv) a hole transport layer operationally connected to and sandwiched between the transparent oxide layer and the perovskite layer. In embodiments, the hole transport layer can comprise nickel oxide / MeO-2PACz. In embodiments, the transparent oxide layer can be selected from indium tin oxide and glass. In embodiments, the perovskite layer can be Cso.o5FAo.9MAo.o5Pb(Io.95Bro.os)3. In other embodiments, the perovskite layer can be an ABC3 perovskite, wherein A and B are cations and C is an anion, wherein A is selected from the group consisting of Cs, FA, MA, and combinations thereof; wherein B is selected from the group consisting of Pb, Sn, and combinations thereof; and wherein C is selected from the group consisting of Cl, I, Br, and combinations thereof. In embodiments, the electrode layer can be silver.

[0008] Still further provided is a photovoltaic device. The photovoltaic device can include (i) a silver electrode layer; (ii) a perovskite layer and an above-described ionic composition; (iii) a transparent oxide layer; (iv) a hole transport layer operationally connected to and sandwiched between the perovskite layer and the transparent oxide layer; and (v) a C60 / BCP group layer operationally connected to and sandwiched between the silver electrode layer and the perovskite layer. In embodiments, the transparent oxide layer can be indium tin oxide. In embodiments, the hole transport layer can comprise nickel oxide / MeO-2PACz.FIGURES

[0009] Fig. 1 shows the interaction between Pbb / PVSK with MEM-MIM-C1 and their properties: (A) molecule structure of MEM-MIM-C1 and commercial ionic liquid BMIM-BF4; (B) picture and absorption spectra of PbI₂, PbI₂:MEM-MIM-Cl and PbI₂: BMIM-BF4 mixtures at a molar ratio of 1.0:0 1; (C) absorption spectra of PVSK, PVSK: MEM-MIM-C1 andPbI₂: BMIM-BF4 mixtures at a molar ratio of 1.0:0.1 (D) XRD of PbI₂, PbI₂: MEM-MIM-Cl and PbI₂: BMIM-BF4 films; (E) XRD of PVSK, PVSK: MEM-MIM-C1 and PVSK: BMIM-BF4 films; (F) steady-state PL spectra of PVSK, PVSK: MEM-MIM-C1 and PVSK: BMIM-BF4 films made on Glass / ITO / SAM substrates, measured from perovskite surface; (G) top-view SEM image of the control perovskite film; (H) top-view SEM image of the PVSK; MEM-MIM-C1 film; (I) topview SEM image of the PVSK: BMIM-BF4 film; (J) grain size distribution of the control perovskite film; (K) grain size distribution of the PVSK: MEM-MIM-C1 film; and (L) grain size distribution of the PVSK: BMIM-BF4 film.

[0010] Fig. 2 illustrates device performance: statistic performance distribution for (A) the distribution of open-circuit voltage (Voc), (B) fill factor (FF), (C) J-V curves under forward and reverse scans for the control with a scan rate of 0.1 V s-1for the control. (D) short-circuit current (J sc), and (E) power conversion efficiency (PCE), MEM-MIM-C1 incorporated PSCs, (F) forward and reverse scan directions for MEM-MIM-C1, (G) external quantum efficiency (EQE) spectra for the PSCs with MEM-MIM-C1. (H) steady-state output of the devices at the maximum power point under 1-sun illumination, and (I) forward and reverse scan directions for BMIM-BF4.

[0011] Fig. 3 presents perovskite films and devices stability: (A) SEM images for control and MEM-MIM-C1 incorporated perovskite films before and after 7 days of continuous illumination at 90°C; (B) XRD deviation of perovskite films under the conditions of 90°C heating combined with continuous light soaking; (C) XRD deviation of perovskite films under the conditions of 85% relative humidity (RH) combined with 65 °C heating, (D) PCE tracking of encapsulated control, MEM-MIM-C1, and BMIM-BF4 devices performed at 90°C combined with 1-sun continuous illumination (no UV filter), and (E) PCE tracking of encapsulated control, MEM-MIM-C1, and BMIM-BF4 devices performed at relative humidity of 85% combined with 65 °C heating.

[0012] Fig. 4 illustrates broader applicability of ionic liquids: (A) the molecule structure of ionic liquids; (B) statistical PSCs with ionic liquidsDESCRIPTION

[0013] Ensuring the higher efficiency and operational stability of devices remains a significant challenge, even with recent advancements in innovative strategies. A series of ionicliquids was developed to enhance device efficiency and stability of perovskite solar cells (PSCs) by regulating perovskite growth, thereby improving perovskite film quality. Data indicate that the ionic liquid methoxyethoxymethyl-1 -methylimidazole chloride (MEM-MIM-C1) can form a complex with Pbb through interactions between the oxygen atoms with lone pairs of electrons and uncoordinated lead (Pb). This interaction facilitates the formation of an intermediate phase during perovskite growth, ultimately enhancing the quality of the resulting perovskite films. Incorporating ionic liquids into the perovskite precursor significantly improves both device efficiency (up to 25.2% powder conversion efficiency) and stability. Notably, devices containing these ionic liquids retained 90% of their initial power conversion efficiency (T90) after 1,300 hours of continuous exposure to illumination while being subjected to heating at 90 °C. This is the first study to evaluate performance under such extreme aging conditions (90 °C heating combined with continuous illumination, no UV filter), and, moreover, the ionic liquid MEM-MIM-C1 has been shown to enhance stability significantly. Furthermore, the other developed ionic liquids have also shown significant improvements in both device efficiency and stability.

[0014] Accordingly, provided is an ionic liquid composition to enhance the stability and efficiency of devices, such as perovskite-containing devices, e.g., perovskite solar cells. The ionic liquid composition comprises at least one compound having a structure selected from:wherein X can be an anion and Y can be O, S, Se, or Te. In various embodiments, the anion can be Cl, Br, I, BF₄, PF₆, acetate, trifluoroacetate, SCN, NOs, C(CN)3, (CH₃O)₂PO₂, HSO4, CH3SO3, CF3SO3, N(CN)2, or N(CF₃SO₂)₂ (also known as Tf2N or TFSI).

[0015] Further provided is a device comprising a perovskite layer and an above-described ionic composition. In embodiments, the ionic composition can compriseMEM-MIMin which X can be Cl. In embodiments, the device can further comprise (i) an electrode layer; (ii) an electron transport layer operationally connected to and sandwiched between the electrode layer and the perovskite layer; (iii) a transparent oxide layer; and (iv) a hole transport layer operationally connected to and sandwiched between the transparent oxide layer and the perovskite layer. In embodiments, the hole transport, layer can comprise nickel oxide / MeO-2PACz. In embodiments, the transparent oxide layer can be selected from indium tin oxide and glass. In embodiments, the perovskite layer can be Cso.osFAovMAo.osPb ovsBro.os):’. In other embodiments, the perovskite layer can be an ABC₃ perovskite, wherein A and B are cations and C is an anion, wherein A can be selected from the group consisting of Cs, FA, MA, and combinations thereof; wherein B can be selected from the group consisting of Pb, Sn, and combinations thereof; and wherein C can be selected from the group consisting of Cl, I, Br, and combinations thereof. In embodiments, the electrode layer can be silver

[0016] Still further provided is a photovoltaic device. The photovoltaic device can comprise (i) a silver electrode layer; (ii) a perovskite layer and an above-described ionic composition; (iii) a transparent oxide layer; (iv) a hole transport layer operationally connected to and sandwiched between the perovskite layer and the transparent oxide layer; and (v) a C60 / BCP group layeroperationally connected to and sandwiched between the silver electrode layer and the perovskite layer. In embodiments, the transparent oxide layer can be indium tin oxide. In embodiments, the hole transport layer can comprise nickel oxide / MeO-2PACz.Examples

[0017] The following examples are intended to illustrate the present disclosure. It is not intended to limit the scope of the claimed invention in any way.Materials

[0018] PbI₂ (99.99%), PbBr₂ (99.999%) and [[2-(3,6-Dimethoxy-9 / 7-carbazol-9-yl)ethyl]phosphonic Acid (MeO-2PACz) were purchased from TCI Chemicals, formamidinium iodide (FAI, 99.99%, GreatCell Solar), methylammonium iodide (MABr, 99.99%, GreatCell Solar), dimethyl sulfoxide (DMSO, 99.9%, Sigma-Aldrich), CsI (99.999%, Sigma Aldrich), anhydrous N, N-dimethyl formamide (DMF, 99.8%, Sigma Aldrich), C60 (Nano-C Inc).Bathocuproine (BCP, 96%), Chlorobenzene (CB), Ethanol and isopropanol were purchased from Sigma-Aldrich. Pipl was purchased from Xi’an Yuri Solar Technology Corp. NiOx was purchased from Liaoning Youxuan New Energy Technology Co., Ltd. All chemicals were directly used without any further purification. Reagents used for ionic liquid synthesis are specified below.Example 1: Interactions between ionic liquids and perovskite

[0019] To enhance device efficiency and stability, an ionic liquid, methoxyethoxymethyl-1-methylimidazole chloride (MEM-MIM-C1) was developed as illustrated in Fig. la (with the synthesis route detailed in the experimental section). To investigate the impact of MEM-MIM-C1 on perovskite growth and crystallization, its interaction with PbI₂ was first examined using the commercial ionic liquid l-Butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) for comparison. As shown in Fig. lb, adding MEM-MIM-C1 to PbI₂ resulted in a noticeable color change from yellow to a lighter shade. The PbI₂ film with MEM-MIM-C1 exhibited a blue shift in the absorption spectrum compared to PbI₂, indicating the formation of a complex similar toPbI₂-Dimethyl sulfoxide (DMSO) Importantly, the ionic liquid did not alter the absorption spectrum of the resulting perovskite films (Fig. 1c).

[0020] The X-ray diffraction (XRD) pattern in Fig. Id reveals a strong peak at 12.7° corresponding to the (001) plane of PbI₂. In contrast, the PbI₂ film containing MEM-MIM-C1 shows reduced intensity at the (001) plane and a new diffraction peak at 2θ = 9.42°, suggesting the formation of the PbI₂: MEM-MIM-Cl adduct. The perovskite film with MEM-MIM-C1 (Fig. le) demonstrates higher peak intensities and sharper diffraction features, indicating improved crystallinity.

[0021] Scanning electron microscopy (SEM) images in Figs. 1g, h, and i, along with grain size distribution in Figs. Ij, k, and I, reveal that the perovskite film with MEM-MIM-C1 film has larger crystal size and a smoother surface with fewer defects. This enhancement can be attributed to the reduction in the perovskite growth rate from the formation of perovskite: MEM-MIM-C1 adducts.

[0022] To assess how MEM-MIM-C1 influences charge carrier dynamics in perovskite films, steady-state photoluminescence (PL) measurements were conducted. As illustrated in Fig. If, the PL spectra of the perovski te films show an emission peak at 790 nm, corresponding to an optical bandgap of 1.57 eV, closely aligning with the absorption spectrum (Fig. 1c). Notably, the PL intensity of the perovskite films with MEM-MIM-C1 was significantly higher than that of the control perovskite film, indicating the formation of high-quality perovskite layers facilitated by the ionic liquid, which contributes to reduced non-radiative recombination processes.Example 2: Devices performance

[0023] The perovskite solar cells (PSCs) studied herein have the following device structure: ITO / NiOx / MeO-2PACz / Cs₀.₀₅FA₀.₉MA₀.₀₅Pb(I₀.₉₅Br₀.₀₅)₃ / PI / C₆₀ / Bathocuproine(BCP) / Silver (Ag). In this device structure, Pl is Piperazinium iodide, NiOx / MeO-2PACz serves as the hole transporting layer, while C60 / BCP functions as the electron transport layer. The device performance was compared with devices with ionic liquids MEM-MIM-C1 and BMIM-BF4.

[0024] Figs. 2a, b, d, and e illustrate the distribution of open-circuit voltage (Voc), fill factor (FF), short-circuit current (Jsc), and power conversion efficiency (PCE) for the control devices and those using ionic liquids. In the reverse scan direction, the control PSCs achieved a PCE of 23.6%, with a Jsc of 24.96 mA cm-2, a Voc of 1.151 V, and an FF of 82.3%, resulting inan average PCE of 22.9% In contrast, the PSCs incorporating ionic liquid MEM-MIM-CI reached the highest PCE of 25.2%, with a Jsc of 25.42 mA cm-2, a Voc of 1.169 V, and an FF of 84.8%, yielding an average PCE of 24.4%. The PSCs with BMIM-BF4 exhibited a PCE of 24.1%.

[0025] Furthermore, the PSCs with MEM-MIM-CI demonstrated reduced J-V hysteresis (Figs. 2c, f, and i) under both forward and reverse scan directions, suggesting less mobile ion migration due to a decrease in defects in the perovskite layer when using MEM-MIM-CI. The external quantum efficiency (EQE) spectra for the PSCs with MEM-MIM-CI are shown in Fig.2g, where the integrated Jsc value from the EQE spectra is 24.8 mA cm-2, indicating a 2% discrepancy between the Jsc values obtained from the EQE spectra and the J-V curve, thus confirming the accuracy of the J-V measurements Finally, Fig. 2h presents the stabilized photocurrent of the devices at the maximum power output point under 1-sun simulated illumination, yielding a stabilized PCE of 24.9% for the MEM-MIM-Cl-incorporated PSCs. The stabilized photocurrent and PCE values are consistent with those measured from the J-V scans.Example 3: Perovskite films and devices stability

[0026] Before assessing the device stability (thermal stability and photostability), the stability of the perovskite films under various aging conditions was investigated, SEM results in Fig. 3a revealed a higher presence of white crystals in the control perovskite films compared to those with MEM-MIM-CI after 7 days of continuous illumination at 90°C. The white crystals are attributed to decomposed Pbh.

[0027] Under light-soaking conditions at 90°C for 10 days, the perovskite films without ionic liquids (Fig. 3b) displayed a prominent Pbb peak at 12.8°. In contrast, the films with MEM-MIM-CI showed no significant Pbh peak, while those with BMIM-BF4 began to exhibit Pbh presence. This indicates that the perovskite films with MEM-MIM-CI possess superior light and heat stability. Additionally, control perovskite films stored for 10 days at 85% relative humidity (RH) and 65°C began to show signs of Pbh and phase transition (5-FAPbh). Similarly, the films with BMIM-BF4 exhibited these changes, while the MEM-MIM-Cl-incorporated perovskite films did not (Fig. 3c).

[0028] To further enhance the operational stability of perovskite solar cells, a device structure of ITO / NiOx / SAM / FA₀.₉₅Cs₀.₀₅PbI₂ / PI / C₆₀ / SnO₂ / Cr / Cu was fabricated. In thisconfiguration, the MA-free FA₀.₉₅Cs₀.₀₅PbI₂ serves as the light-absorbing layer, with atom layer deposition SnO₂ acting as the hole-blocking layer. The Ag electrodes were replaced with Cr / Cu to mitigate instability caused by Ag corrosion and diffusion.

[0029] The impact of ionic liquids on device stability under continuous illumination at 90°C in a nitrogen environment was first evaluated. As shown in Fig. 3d, the control device exhibited a rapid efficiency decline, dropping to 80% of its initial value (22.8%) after 170 hours and below 50% after 900 hours. In contrast, devices incorporating MEM-MIM-Cl demonstrated almost no efficiency loss after 100 hours, retaining 90% of their initial value (24.1%) after over 1,300 hours, even under the harsh conditions of 90°C combined with continuous 1 -sun illumination. Notably, this study is the first to evaluate device stability under such extreme aging conditions (90°C with continuous illumination) and achieve high stability. The instant ionic liquid was sent to First Solar California Technology for performance certification, where similar results were observed. Devices with MEM-MIM-Cl demonstrated the best efficiency and highest stability (results cannot be shown here due to conflicts of interest). For comparison, devices using the commercial ionic liquid BMIM-BF4 showed faster degradation than those with MEM-MIM-Cl. Additionally, devices with MEM-MIM-Cl exhibited significantly less degradation compared to control devices and those with BMIM-BF4 under conditions of 85% relative humidity and 65°C (Fig. 3d),

[0030] These results suggest the important role of ionic liquid design in assisting perovskites growth and crystallization to enhance crystal size and reduce defects. Importantly, other developed ionic liquids could similarly enhance device efficiency (Fig. 4) and stability. This suggests that ionic liquids have broader applicability in improving device performance. Furthermore, perovskites with the ABX3 structure (where A = Cs, FA, or MA; B = Pb or Sn; X = Cl, Br, or I) would benefit from the incorporation of ionic liquids, resulting in improved quality and performance across both pin and nip structure devices, whether they are wide bandgap perovskites (Eg > 1.7 eV), all-inorganic FA / MA-free perovskites, or narrow bandgap perovskites (Eg < 1,4 eV).Example 4: Chloride-based Ionic liquid Synthesis

[0031] Ionic liquids with chloride anion were synthesized in neat condition in one pot inside a N₂-filled glovebox. In a flame-dried flask, 1 -methylimidazole (1 equiv.) was slowly added to2-methoxyethoxymethyl chloride (MEM-CI, Millipore Sigma #357480 technical grade, 4-5 equiv.), or ethoxychloromethane (EOM-C1, Millipore Sigma #14267095%, 4-5 equiv.), or chloromethyl methyl sulfide (MSM-C1, Millipore Sigma #C5400795%, 4-5 equiv.) while stirring. The addition was completed with a syringe pump at 10 mL / h. The mixture was stirred at room temperature for 8-24 hours, after which volatiles were removed using rotary evaporation at 60-70°C and 50 mbar. The remaining liquid was cooled to room temperature before removed from vacuum. Further purification was done by adding anhydrous diethyl ether to the mixture - while ether won’t dissolve the ionic liquid product, the impurities will be dissolved into the ether phase under vigorous stirring. Then, the ether phase with impurity was decanted. Concentration of the ether phase gave a viscous dark yellow liquid. The remaining product as a pale-yellow dense liquid was dried under vacuum and stored inside the glovebox. The yield was quantitative.

[0032] It should be noted that moisture control was essential to obtain targeted chloridebased ionic liquids with minimum amount of impurity, as the trace amount of water would hydrolyze the chloride side chain (e g. MEM-CI) and introduce HC1 to the reaction mixture. HC1 then protonated the reactant 1 -methyl imidazole into 1 -methylimidazolium chloride, which stayed in the final product.Example 5: Ionic Liquid Anion Exchange

[0033] MEM- IM Cl (1 equiv.) was dispensed in anhydrous acetone to make a 1 M mixture, to which NaBFri, NaTfN, or NaOTf (1.2 equiv.) was added. The mixture was rigorously stirred for 8 hours, during which the initial heterogenous mixture turned homogenous. NaCl was formed during the anion exchange process, which was easily removed by filtering the mixture through a PTFE syringe filter. The acetone solution was then concentrated to give a greenish brown viscous liquid (regardless of the anion) Yet, diacetone alcohol, a major impurity came with acetone, was identified as the major leftover impurity. Thus, the crude product was further purified by first dispensed it in 1 M anhydrous chloroform and subsequently reprecipitation with anhydrous ether.Example 6: Device fabrication

[0034] NiO2 nanocrystal (10 mg mL⁻¹) layers were first spin coated on ITO substrates at3,000 r.p.m. for 30 s in air, then the substrates were immediately heated at 150 C for 15 mins. After that the substrates were immediately transferred to the glovebox. MeO-2PACz(0.5 mg mb1) in ethanol was spin coated on the NiO film at 5,000 r.p.m. for 30 s and then annealed at 100 °C for 10 min. Perovskite precursor solution (1 5 M, Cso.osFAo.9MAo.o5Pb(Io.95Bro.os)3) was prepared by dissolving the Pbh, PbBn, MABr, CsI, and FAI in a mixture of solvents DMF and DMSO at a volume ratio of 4: 1. For the perovskite film fabrication, the substrate was spun at 1500 r.p.m. for 10 s with an acceleration of 1,000 r.p.m. per second at first, and then at 5,000 r.p.m. for the 35 s with an acceleration of 7,000 r.p.m. per second. In the second step, 300 μL Anisole was dropped onto the substrate during the last 15 s of the spinning. The substrate was immediately placed on a hotplate and annealed at 100 °C for 10 min. For the posttreatment, the Pipl were dissolved in IPA solution with concentration of 0.5 mg mF1, and spun-coated onto the perovskite film surface at a spin rate of 4,000 r.p.m. for 30 seconds. The film was then annealed at 100 °C for 5 min to remove any residual IPA. After cooling to room temperature, the substrates were transferred to the evaporation system, 20 nm Ceo, 8 nm BCP and 100 nm Ag were subsequently deposited by thermal evaporation.

[0035] For PSCs used in stability tracking, 8 nm of BCP was replaced with 20 nm of atomic-layer-deposited Tin(IV) oxide (ALD-SnCh) to limit environmentally induced degradation. Deposition of the ALD-SnO2 was carried out using a PICOSUN R-200 Advanced ALD system. Water and tetrakis(dimethylamino)Tin(IV) were used as oxygen and tin precursors, respectively. The precursor and substrate temperature were set to 75 °C and 85 °C, respectively. Nitrogen gas (90 seem) was used as carrier gas.Example 7: Encapsulation of perovskite solar cells

[0036] Perovskite solar cells were encapsulated with cover glass and epoxy resin (Devcon epoxy Tube 14250) on the side.Example 8: Films and devices characterization

[0037] The XRD patterns were analyzed using a Rigaku SmartLab equipped with a PhotonMax high-flux 9 kW rotating anode X-ray source (Cu Kα = 1.54178 Å), an in-plane arm (5-axis goniometer), and a HyPix-3000 high-energy resolution 2D HPAD detector. SEM images were captured using a Hitachi S-4800 SEM operating at 5.0 kV with a secondaryelectron detector. UPS were obtained using an H Lyman-α photon source (E-LUXTM 121) with a 5 V negative bias. The photon energy used was 10.2 eV, and the pass energy was 5.85 eV. PL were recorded on a SpectraPro HRS-300, while UV-vis absorption spectra were obtained using a Cary 5000 UV-Vis-NIR Spectrophotometer. The cross-sectional specimens for TEM were prepared using a Thermo Scientific Helios G4 UX Dual Beam. The TEM images and EDS mapping were obtained using a Thermo Scientific Themis Z at an accelerating voltage of 80 kV.

[0038] The J-V characteristics measurement procedure was conducted as follows: J-V curves were recorded inside a N2 glove box using a solar simulator (Enlitech SS-F5-3A) with an intensity equivalent to 1 sun and AM 1.5G irradiation generated by a Xe lamp. The light intensity of 100 mW cm"2was calibrated before each use, utilizing a standard Si reference cell certified by NREL, and the active area of each device was determined using an Olympus microscope. EQE measurements were carried out at zero bias in an atmospheric environment on a custom-built setup equipped with a preamplifier and a lock-in amplifier operating at a chopper frequency of 161 Hz. The light source was also calibrated using a Si diode (818-UV-L).Definitions

[0039] The term ‘"about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[0040] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range were explicitly recited. For example, a range of “about 0.1% to about 5%” or “about 0.1% to 5%” should be interpreted to include not just about 0.1% to about 5%, but also the individual values e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.

[0041] In this document, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to anonexclusive “or” unless otherwise indicated In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting. Further, information that is relevant to a section heading may occur within or outside of that particular section.

[0042] Various modifications and variations of the described compositions, methods, and uses of the technology will be apparent to those skilled in the art without departing from the scope and spirit of the technology as described. Although the technology has been described in connection with specific exemplary embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention that are obvious to those skilled in the art are intended to be within the scope of the following claims.

[0043] All publications and patents mentioned herein are incorporated by reference in their entireties for all purposes. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.Enumerated Embodiments (EE)

[0044] The following list of enumerated embodiments presents claims with multiply dependent claims depending from multiply dependent claims for presentation in those jurisdictions where such dependencies are allowed as well as additional claims, which may be presented during the examination of the application or any divisional or continuation thereof.

[0045] EE 1. An ionic liquid composition comprising at least one compound having a structure selected from:wherein X is an anion and Y is O, S, Se, or Te.

[0046] EE 2 The ionic liquid composition of EE 1, wherein the compound has the structure:

[0047] EE 3. The ionic composition of EE 1 or EE 2, wherein the anion is Cl, Br, I, BF4, PF6, acetate, trifluoroacetate, SCN, NO3, C(CN)3, (CEbOjzPC, HSO4, CH3SO3, CF3SO3, N(CN)2, or N(CF3SO2)2 (also known as TtcN or TFSI)

[0048] EE 4. The ionic composition of EE 1 or EE 2, wherein X is Cl.

[0049] EE 5 A device comprising a perovskite layer and an ionic composition comprising at least one compound having a structure selected from:

[0050] EE 6. The device of EE 5, wherein the anion is Cl, Br, I, BF-i, PFs, acetate, trifluoroacetate, SCN, NCh, C(CN)3, (CEEO^PC, HSCri, CH3SO3, CF3SO3, N(CN)2, or N(CF3SO2)2 (also known as TfzN or TFS1).

[0051] EE 7. The device of EE 5 or EE 6, wherein the compound has the structure:

[0052] EE 8. The device of EE 5 or EE 7, wherein Xis Cl.

[0053] EE 9. The device of any one of EE 5-EE 8, which further comprises:(i) an electrode layer;(ii) an electron transport layer operationally connected to and sandwiched between the electrode layer and the perovskite layer,(iii) a transparent oxide layer; and(iv) a hole transport layer operationally connected to and sandwiched between the transparent oxide layer and the perovskite layer.

[0054] EE 10 The device of claim 9, wherein the hole transport layer comprises nickel oxi de / MeO -2PA Cz.

[0055] EE 11 The device of EE 9 or EE 10, wherein the transparent oxide layer is selected from indium tin oxide and glass.

[0056] EE 12. The device of any one of EE 5- EE 11, wherein the perovskite layer is C so. o 5 FA o. sMAo.o 5 Pb ( Io.95 B ro.05)3.

[0057] EE 13. The device of any one of EE 9- EE 11, wherein the perovskite layer is an ABC₃ perovskite, wherein A and B are cations and C is an anion, wherein A is selected from the group consisting of Cs, FA, M A, and combinations thereof; wherein B is selected from the group consisting of Pb, Sn, and combinations thereof; and wherein C is selected from the group consisting of Cl, I, Br, and combinations thereof.

[0058] EE 14. The device of any one of EE 9- EE 13, wherein the electrode layer is silver.

[0059] EE 15. The device of any one of EE 9-EE 14, wherein the compound has the structure:

[0060] EE 16. The device of EE 15, wherein X is Cl.

[0061] EE 17. A photovoltaic device comprising:(i) a silver electrode layer,(ii) a perovskite layer and an ionic composition of claim 1 or 2;(iii) a transparent oxide layer;(iv) a hole transport layer operationally connected to and sandwiched between the perovskite layer and the transparent oxide layer; and(v) a C60 / BCP group layer operationally connected to and sandwiched between the silver electrode layer and the perovskite layer.

[0062] EE 18. The photovoltaic device of EE 17, wherein the transparent oxide layer is indium tin oxide.

[0063] EE 19. The photovoltaic device of EE 17 or EE 18, wherein the hole transport layer comprises nickel oxide / MeO-2PACz.

[0064] EE 20. The photovoltaic device of any one of EE 17-EE 19, wherein the compound has the structure:

[0065] EE 21. A thin film comprising an ionic liquid composition of any one of EE 1 - EE 4.

Claims

WHAT IS CLAIMED IS:

1. An ionic liquid composition comprising at least one compound having a structure selected from:wherein X is an anion and Y is O, S, Se, or Te,2. The ionic liquid composition of claim 1, wherein the compound has the structure:

3. The ionic composition of claim 1, wherein the anion is Cl, Br, I, BF4, PF6, acetate, trifluoroacetate, SCN, NO3, C(CN)3, (CH3O)2PO2, HSO4, CH3SO3, CF3SO3, N(CN)2, or N(CF3SO2)2(also known as Tf2N or TFSI).

4. The ionic composition of claim 2, wherein X is CL5. A device comprising a perovskite layer and an ionic composition comprising at least one compound having a structure selected from:

6. The device of claim 5, wherein the anion is Cl, Br, I, BF4, PF6, acetate, trifluoroacetate, SCN, NO3, C(CN)3, (CH3O)2PO2, HSO4, CH3SO3, CF3SO3, N(CN)2, or N(CF3SO2)2 (also known as Tf2N or TFSI).

7. The device of claim 5, wherein the compound has the structure:

8. The device of claim 7, wherein X is Cl.

9. The device of claim 5, which further comprises:(i) an electrode layer;(ii) an electron transport layer operationally connected to and sandwiched between the electrode layer and the perovskite layer;(iii) a transparent oxide layer; and(iv) a hole transport layer operationally connected to and sandwiched between the transparent oxide layer and the perovskite layer.

10. The device of claim 9, wherein the hole transport layer comprises nickel oxide / MeO 2PACz.

11. The device of claim 9, wherein the transparent oxide layer is selected from indium tin oxide and glass.

12. The device of claim 5, wherein the perovskite layer is Cso.o5FAo.9MAo.o5Pb(Io.95Bro.o5)3.

13. The device of claim 9, wherein the perovskite layer is an ABC₃ perovskite, wherein A and B are cations and C is an anion, wherein A is selected from the group consisting of Cs, FA, MA, and combinations thereof; wherein B is selected from the group consisting of Pb, Sn, and combinations thereof; and wherein C is selected from the group consisting of Cl, I, Br, and combinations thereof.

14. The device of any claim 9, wherein the electrode layer is silver.

15. The device of claim 9, wherein the compound has the structure:

16. The device of claim 15, wherein X is Cl.

17. A photovoltaic device comprising:(i) a silver electrode layer;(ii) a perovskite layer and an ionic composition of claim 1 or 2;(iii) a transparent oxide layer;(iv) a hole transport layer operationally connected to and sandwiched between the perovskite layer and the transparent oxide layer; and(v) a C60 / BCP group layer operationally connected to and sandwiched between the silver electrode layer and the perovskite layer.

18. The photovoltaic device of claim 17, wherein the transparent oxide layer is indium tin oxide.

19. The photovoltaic device of claim 17, wherein the hole transport layer comprises nickel oxide / MeO-2PACz.

20. The photovoltaic device of claim 17, wherein the compound has the structure21. A thin film comprising an ionic liquid composition of claim 1.

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