Critical Role of Functional Groups in Defect Passivation and Energy Band Modulation in Efficient and Stable Inverted Perovskite Solar Cells Exceeding 21% Efficiency.

Interfaces in perovskite solar cells (PSCs) are closely related to their power conversion efficiency (PCE) and stability. It is highly desirable to minimize the interfacial nonradiative recombination losses through rational interfacial engineering. Herein we develop an effective and easily reproducible interface engineering strategy where three mercaptobenzimidazole (MBI)-based molecules are employed to modify the perovskite/electron transport layer (ETL) interface. MBI and MBI-OCH can not only passivate defects at surface and grain boundaries (GBs) of perovskite films but can also improve energy level alignment (ELA), which leads to enhanced PCE and stability. Consequently, the PCE is improved from 19.5% for the control device to 21.2% for MBI-modified device, which is among the best reported inverted MAPbI-based PSCs. In contrast, incorporation of MBI-NO increases defect density and negligibly influences the energy level alignment. This work indicates that defect passivation and ELA modulation can be achieved simultaneously through modulating functional groups in interface modification molecules.