Synergistic Optimization of Buried Interface by Multifunctional Organic–Inorganic Complexes for Highly Efficient Planar Perovskite Solar Cells

Highlights Highly performed perovskite solar cells are achieved via introducing organic–inorganic CL–NH complex as multifunctional interfacial layer. CL–NH complex not only reduces oxygen vacancies on the surface of SnO2 but also regulates film crystallization, resulting in a superior device efficiency of 23.69%. The resulting device performs excellent stability with 91.5% initial power conversion efficiency retained after 500 h light illumination. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-023-01130-5.


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). 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 30 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 steady-state current density at the maximum-powerpoint 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. The elemental distribution in perovskite film was characterized using PHI nanoTOF II Time-of-Flight SIMS.

S2.1 General Information
All syntheses were carried out under an inert atmosphere (nitrogen) using standard Schlenk techniques unless otherwise stated. The osmapentalene derivates 1, 2(CL-Ph), 3(CL-NH), 4(CL-BPh) were synthesized according to the published literatures [S1-S3]. 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 tetramethyl silane, and 31 P{ 1 H} NMR chemical shifts are relative to 85% H3PO4. 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.

S2.2 Preparation and Characterization of 2
Phenylacetylene (55 μL, 0.50 mmol) was added to a mixture of complex 1 (115 mg, 0.10 mmol) and AgBF4 (58 mg, 0.30 mmol) in 10 mL wet dichloromethane. The reaction mixture was stirred at room temperature for 3 h to give a yellow-green 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 green band was collected, and the solvent was evaporated to dryness under vacuum. The resultant residue was washed with diethyl ether and then dried under vacuum to obtain a green solid of complex CL-Ph. Yield, 77 mg, 56%.

S2.3 Preparation and Characterization of 3a
Wet dichloromethane (10 mL) was added to a mixture of complex 1 (115 mg, 0.10 mmol), 1ethynyl-4-nitrobenzene (74 mg, 0.50 mmol) and AgBF4 (58 mg, 0.30 mmol). The reaction mixture was stirred at room temperature for 3 h to give a yellow-green 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 green band was collected, and the solvent was evaporated to dryness under vacuum. The resultant residue was washed with diethyl ether to obtain a yellow-green solid of complex 3a, which was dried under vacuum. Yield, 88 mg, 60%.

S2.4 Preparation and Characterization of CL-NH
A solution of the complex 3a (88mg, 0.06 mmol) in methanol (10 mL) and concentrated HCl (0.5 mL) was carefully treated with zinc dust (39 mg, 0.60 mmol) at 0 °C. The suspension was stirred at 0 °C for 30 min and room temperature for 30 min. A saturated aqueous NaHCO3 solution was slowly added. The mixture was extracted using dichloromethane and NaBF4 was added. The mixture was stirred at room temperature for 1 h, and then the solid suspension was removed by filtration. The filtrate was reduced under vacuum to approximately 2 mL, and then loaded on silica gel column eluted by dichloromethane/methanol (20/1). The green band was collected, and the solvent was evaporated to dryness under vacuum. The resultant residue was washed with diethyl ether to give a yellow-green solid of complex CL-NH. Yield, 76 mg, 91%.

S2.5 Preparation and Characterization of CL-BPh
A solution of NaBPh4 (9 mg, 0.026 mmol) in methanol (0.5 mL) was added to a solution of complex CL-NH (28 mg, 0.02 mmol) in methanol (2 mL  Note: This energy shift is mainly ascribed to the interaction between high electron negative F atoms in BF4anion and SnO2 films, which is further verified by the lower energy shift of F 1s spectra.  Note: As shown in Fig. S29, no pinholes can be observed from the control and CL-Ph films. Only some valleys between adjacent crystals, as marked in white, can be observed. However, for the CL-BPh and CL-NH films (Fig. S29c,d), there are some pinholes (marked in red), which are totally different from the adjacent crystal valleys, as supported by the insert enlarged images, can be clearly observed. These pinholes can facilitate the penetration of organic salt, which further improve the crystallinity of the resulting perovskite film.     It is noted that the control and CL-Ph films show an average grain size at around 500 nm, while, the CL-BPh and CL-NH films show much larger grain size at around 1150 nm. The significant enhancement on grain size after CL-BPh and CL-NH modification is mainly attributed to the improvement of film crystallinity due to the interaction between -NH2 group and PbI2.  Note: According to the TPC results, the fastest charge extraction time 0.84 us derived from CL-NH device indicates an enhanced charge extraction efficiency, which is responsible for the highest Jsc, and detail parameters summarized in Table S5.