Anchoring Vertical Dipole to Enable Efficient Charge Extraction for High‐Performance Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs) via two‐step sequential method have received great attention in recent years due to their high reproducibility and low processing costs. However, the relatively high trap‐state density and poor charge carrier extraction efficiency pose challenges. Herein, highly efficient and stable PSCs via a two‐step sequential method are fabricated using organic—inorganic (OI) complexes as multifunctional interlayers. In addition to reduce the under‐coordinated Pb2+ ions related trap states by forming interactions with the functional groups, the complexes interlayer tends to form dipole moment which can enhance the built‐in electric field, thus facilitating charge carrier extraction. Consequently, with rational molecular design, the resulting devices with a vertical dipole moment that parallels with the built‐in electric field yield a champion efficiency of 23.55% with negligible hysteresis. More importantly, the hydrophobicity of the (OI) complexes contributes to an excellent ambient stability of the resulting device with 91% of initial efficiency maintained after 3000 h storage.

were set at 450eV，10 -5 eV and 0.02eV Å −1 respectively in all calculations. We used a 2×2×1 gamma centered k-point grid generated by the Monkhorst-Pack scheme for two passivation models of FAPbI 3 (001) surface structures (368 atoms) passivated by CL-CH 3 and CL-CF 3 molecules. All electrostatic potential (ESP) of molecules was calculated based on all-electron double-ξ valence basis sets of LanL2DZ.
Characterizations: The crystal structure and phase of the perovskite were characterized using X-ray diffraction spectrometer were obtained on Bruker Advanced D8 X-ray diffractometer using Cu Kα (λ = 0.154 nm) radiation. A UV-Vis spectrophotometer (Agilent Cary 5000) was used to collect the absorbance spectra of the perovskite films. Steady state photoluminescence (PL) spectra were recorded on Shimadzu RF-5301pc. Time-resolved photoluminescence spectra were measured on a PL system (Fluo-Time 300) under excitation with a picosecond pulsed diode laser with a repetition frequency of 1 MHz. The morphology of the films was studied by field-emission scanning electron microscopy (SEM; TESCAM MIRA3). The surface potential of perovskite films obtained with a atomic force microscope (AFM; Asylum Research MFP-3D-Stand Alone). An FEI Helios Nanolab 600i dual beam, focus ion beam/field emission gun-scanning electron microscope (FIB/FEGSEM) (FEI, Netherland), was used to prepare the device cross-section for scanning transmission electronic microscopy (STEM) imaging and analysis (FEI, Netherland). X-ray photoelectron spectroscopy (XPS) was conducted on a Thermo ScientificTM K-AlphaTM+ spectrometer equipped with a monochromatic Al Kα X-ray source (1486.6 eV) operating at 100 W. Samples were analyzed under vacuum (P < 10−8 mbar) with a pass energy of 150 eV (survey scans) or 50eV (high-resolution scans). The XPS spectra were calibrated by the binding energy of 284.8 eV for C 1s. Ultraviolet photoelectron spectroscopy (UPS, ESCALAB 250Xi, Thermo Fisher) measurements were carried out using a He Iα photon source (21.22 eV). The current density-voltage (J-V) curves of fabricated devices were obtained from the forward and reverse scan with 10 mV intervals and 10 ms delay time under AM 1.5 G illumination (100 mW cm −2 ) were collected using a source meter (Keysight B2901A) and a solar simulator (Enlitech SS-F5-3A). The EQE spectra was measured using an quantum efficiency measurement system (Enlitech QER-3011) in which the light intensity at every wavelength was calibrated with a Si detector before measurement. The maximum-power point (MPP) output was measured by testing the steadystate current density at the maximum-power-point voltage. Electrochemical impedance spectroscopy (EIs) was tested with the frequency range from 100 Hz to 1 MHz by the electrochemical workstation (Princeton Applied Research, P4000+) in the dark conditions at with a bias of 1 V. The amplitude is 10 mV.
Statistical Analysis: In order to facilitate comparison, part of the data is normalized, such as the timeresolved PL (TRPL) results ( Figure 4b in the revised manuscript) and the stability results (Figure 5a-c and Figure S24 in the revised manuscript). The statistical results were obtained by presenting the photovoltaic parameters of different number of devices. The sample size, specific test, and data presentation of each statistical analysis was specified in the corresponding figure legend. The TRPLcurves were fitted using OriginLab software. The scale bars of SEM, TEM and AFM images ( Figure  S17, Figure S18 and Figure S19 in the revised manuscript) were presented in the corresponding figure and specified in the figure legend. Specific details for all methods and softwares are discussed in the Characterization Section. Relavent content has been added in the revised manscript on page .

General information
All syntheses were carried out under an inert atmosphere (nitrogen or argon) using standard Schlenk techniques unless otherwise stated. Solvents were distilled under nitrogen from sodium/benzophenone (diethyl ether) or calcium hydride (dichloromethane) prior to use. The osmapentalyne 1 was synthesized according to the published literatures [1] . The other reagents and solvents were used as purchased from commercial sources without further purification. Column chromatography was performed on silica gel (200-300 mesh) in air. NMR spectra was collected on a Brucker AVANCE NEO 400 spectrometer (400 MHz) or Brucker AVANCE NEO 600 spectrometer (600 MHz). 1 H and 13 C{ 1 H} NMR chemical shifts (δ) are relative to tetramethylsilane, and 31 P{ 1 H} NMR chemical shifts are relative to 85% H 3 PO 4 . Two-dimensional and one-dimensional NMR spectra are abbreviated as HSQC (heteronuclear single quantum coherence), HMBC (heteronuclear multiple bond coherence) and DEPT (distortionless enhancement by polarization transfer). The absolute values of the coupling constants are given in hertz (Hz). Multiplicities are abbreviated as s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet) and br (broad). The high-resolution mass spectra (HRMS) experiments were performed on a Thermo Scientific Q Exactive instrument.

Preparation and characterization of CL-CH 3
A mixture of compound 1 (120 mg, 0.10 mmol), 4-methylphenol (54 mg, 0.50 mmol) and Cs 2 CO 3 (163 mg, 0.50 mmol) in 10 mL dichloromethane was stirred at RT for 1 d to give a red solution, and then the solid suspension was removed by filtration. The volume of the filtrate was reduced under vacuum to approximately 2 mL, and then loaded on silica gel column eluted by dichloromethane/methanol (20/1). The red band was collected, and the solvent was evaporated to dryness under vacuum to give a red solid. Yield, 99 mg, 78%.

Preparation and characterization of CL-CF 3
A mixture of compound 1 (120 mg, 0.10 mmol), 4-trifluoromethylphenol (81 mg, 0.50 mmol) and Cs 2 CO 3 (163 mg, 0.50 mmol) in 10 mL dichloromethane was stirred at RT for 1 d to give a red solution, and then the solid suspension was removed by filtration. The volume of the filtrate was reduced under vacuum to approximately 2 mL, and then loaded on silica gel column eluted by dichloromethane/methanol (20/1). The red band was collected, and the solvent was evaporated to dryness under vacuum to give a red solid. Yield, 95 mg, 72%.

X-ray Crystallographic Analysis
The single crystals suitable for X-ray diffraction was grown from chloroform solution layered with hexane. Single-Crystal X-ray diffraction data were collected on a Bruker SMART APEX2 area detector diffractometer with a Cu Kα radiation (λ = 1.54184 Å). Multi-scan absorption corrections was applied for CL-CH 3 . Using Olex2 [2] , the structure of CL-CF 3 was solved with ShelXT [3] structure solution program using Intrinsic Phasing and refined with the ShelXL [4] refinement package using Least Squares minimization. All non-hydrogen atoms were refined anisotropically unless otherwise stated. Hydrogen atoms were placed at idealized positions and assumed the riding model. The diffuse electron densities resulting from the residual solvent molecules in complex CL-CF 3 was removed from the data set by using the Solvent Mask routine of Olex2. CCDC-2160622 (CL-CF 3 ) contain supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre. Figure S10. X-ray molecular structure for the cation of complex CL-CF 3 drawn with 50% probability level.
Note: Thermogravimetric analyses (TGA) of CL-CH 3 and CL-CF 3 show that the initial decomposition temperatures (T5) as measured at the point of 5% weight loss are 217.1 ℃ and 207.6 ℃ , respectively.  Note: According to density functional theory (DFT), the dipole moments of CL-CF3 and CL-CH3 are 8.4 D and 11.04 D, respectively. due to the existence of strong electron-withdrawing Trifluoromethyl (-CF 3 ) group, CL-CF 3 exhibits higher dipole moment of than that of CL-CH 3 due to the existence of strong electron-withdrawing Trifluoromethyl (-CF 3 ) group. Figure S13. FTIR spectra and fingerprint regions of pure PbI 2 , CL-CH 3 , CL-CF 3 , PbI 2 +CL-CH 3 and PbI 2 +CL-CF 3 mixture in DMSO.
Note: The stretching vibration of C=O bond shifted from 1660 cm −1 in pure CL-CH 3 and CL-CF 3 molecules to a lower wavenumber of 1643 cm −1 for the PbI 2 +CL-CH 3 and PbI 2 +CL-CF 3 samples. Figure S14. a) XPS survey spectra of control, CL-CH 3 and CL-CF 3 films. b-d) Os 4f core spectra, c) P 2p core spectra, and d) F 1s core spectra of control, CL-CH 3 , CL-CF 3 films, respectively.
Note: It can be seen from the XPS survey spectra that control, CL-CH 3 and CL-CF 3 perovskite films all contain Pb, I, Cl, C, N, O. The appearance of Os 4f, P 2p and F 1s signal indicates the existence of OI complexes in the final film. Figure S15. a) Pb 4f core spectra of perovskite films without and with CL-CH 3 and CL-CF 3 treatment. b) F 1s core spectra of PbI 2 +CL-CF 3 and CL-CF 3 film.
Note: The Pb 4f peaks of control film are consistent with the reported binding energies of constituent elements of perovskite material, where Pb 4f 5/2 and Pb 4f 7/2 peaks are 143.1 and 138.2 eV, respectively. In the case of Pb 4f 5/2 and Pb 4f 7/2 of CL-CH 3 and CL-CF 3 treatment perovskite film, the peaks are 142.8, 137.97 eV and 142.7, 137.94 eV, respectively. The F 1s peaks of pure CL-CF 3 are 688.2eV. The F 1s peaks of PbI 2 + CL-CF 3 are 687.9eV. Figure S16. XRD patterns of CL-CH 3 , CL-CF 3 modified and control perovskite films.
Note: The XRD results suggest that the OI complexes will not affect the crystallinization.      Table S1. density and voltage at the SCLC region. After carefully calculation, the hole mobility of control, CL-CH 3 , and CL-CF 3 films located at 3.8×10 -2 , 4.2×10 -2 , and 5.7×10 -2 cm -2 V -1 S -1 , respectively. The results suggest that CL-CF 3 complex can effectively improve the hole mobility of the film.

Figure S24
The operational stability of the corresponding unencapsulated devices under continuous 1 sun illumination in ambient environment.
Note: It is noted that after 32 hours illumination, the control device only retained 61% of its initial efficiency. In comparison, the CL-CH 3 device maintained 75% of its initial efficiency after 40 hours measurement. While, for the CL-CF 3 device, over 80% of its initial efficiency was maintained after 72 hours measurement.