Interface engineering mediated by a designed chemical agent is of paramount importance for developing high-performance perovskite solar cells (PSCs). It is especially critical for planar SnO2-based PSCs due to the presence of abundant surface defects on SnO2 and/or perovskite surfaces. Herein, a novel multifunctional agent histidine (abbreviated as His) capable of cross-linking SnO2 and perovskite is employed to modify the SnO2/perovskite interface. Density functional theory (DFT) calculations and experimental results demonstrate that the carboxylate oxygen of His can form a Sn-O bond to fill the oxygen vacancies on the surface of SnO2, while its positively charged imidazole ring can occupy the cationic vacancies and its -NH3+ group interacts with the I- ion on the perovskite lattice. This cross-linking contributes to the significantly decreased interfacial trap state density and nonradiative recombination loss. In addition, it facilitates electron extraction/transfer and also improves interfacial contact and the quality of perovskite film. Correspondingly, the His-modified device delivers a superior power conversion efficiency (PCE) of 22.91% (improved from 20.13%) and an excellent open-circuit voltage (Voc) of 1.17 V (improved from 1.11 V), along with significantly suppressed hysteresis. Furthermore, the unencapsulated device based on His modification shows much better humidity and thermal stability than the pristine one. The present work provides guidance for the design of innovative multifunctional interfacial material for highly efficient PSCs.
Keywords: defect passivation; density functional theory calculations; histidine; interfacial modification; perovskite solar cells.