Multifunctional Small Molecule as Buried Interface Passivator for Efficient Planar Perovskite Solar Cells

Abstract The improvement of power conversion efficiency (PCE) and stability of the perovskite solar cell (PSC) is hindered by carrier recombination originating from the defects at the buried interface of the PSC. It is crucial to suppress the nonradiative recombination and facilitate carrier transfer in PSC via interface engineering. Herein, P‐biguanylbenzoic acid hydrochloride (PBGH) is developed to modify the tin oxide (SnO 2 )/perovskite interface. The effects of PBGH on carrier transportation, perovskite growth, defect passivation, and PSC performance are systematically investigated. On the one hand, the PBGH can effectively passivate the trap states of Sn dangling bonds and O vacancies on the SnO 2 surface via Lewis acid/base coordination, which is conducive to improving the conductivity of SnO 2 film and accelerating the electron extraction. On the other hand, PBGH modification assists the formation of high‐quality perovskite film with low defect density due to its strong interaction with PbI 2 . Consequently, the PBGH‐modified PSC exhibits a champion power conversion efficiency (PCE) of 24.79%, which is one of the highest PCEs among all the FACsPbI 3 ‐based PSCs reported to date. In addition, the stabilities of perovskite films and devices under high temperature/humidity and light illumination conditions are also systematically studied.