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

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 SnO₂ 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.