Strengthening Durability of Electron Selective Layer and Interface via Trifluoromethoxy‐Functionalized Biguanide Cation Toward High‐performance Air‐Processed n‐i‐p Perovskite Solar Cells

Abstract The poor stability of the electron‐selective layer (ESL) and buried interface hampers the realization of long‐term operationally stable air‐processed n‐i‐p perovskite solar cells (PSCs). Herein, ESL and the buried interface are stabilized through a trifluoromethoxy‐functionalized biguanide cation strategy. The multisite 1‐[4‐(trifluoromethoxy) phenyl] biguanide hydrochloride (TOPBCl) is pre‐embedded in SnO 2 nanoparticles to fulfil simultaneous manipulation of both ESL and buried interface. The rich chemical bonds are formed at the buried interface by the synergy of trifluoromethoxy and biguanide cation, accomplishing a chemical bridge between ESL and perovskite layer, which enables dropped interface defects, facilitates perovskite crystallization, and ameliorates energy band alignment. Owing to saliently suppressed interfacial non‐radiative recombination, the TOPBCl‐modified PSCs achieve an excellent power conversion efficiency (PCE) of 25.79%, which is one of the highest efficiencies reported for air‐processed PSCs. Benefiting from reinforced longevity of ESL and buried interface, the unencapsulated TOPBCl‐modulated devices demonstrate superior operational stability, maintaining 90.04% of their initial PCE after 927 h of continuous maximum power point tracking at 40 ± 5°C. This study provides a biguanide cation functionalization strategy to synchronously stabilize ESL and interface for realizing high‐performance air‐processed PSCs.