Three‐dimensional (3‐D) fluoride molecular glue to improve the SnO2/perovskite interface for efficient perovskite solar cells

Aiming at numerous defects at SnO2/perovskite interface and lattice mismatch in perovskite solar cells (PSCs), we design a kind of three‐dimensional (3D) molecular glue (KBF4‐TFMSA), which is derived from strong intramolecular hydrogen bonding interaction between potassium tetrafluoroborate (KBF4) and trifluoromethanesulfonamide (TFMSA). A remarkable efficiency of 25.8% with negligible hysteresis and a stabilized power output of 25.0% have been achieved, in addition, 24.57% certified efficiency of 1 cm2 device is also obtained. Further investigation reveals that this KBF4‐TFMSA can interact with oxygen vacancies and under‐coordinated Sn(IV) from the SnO2, in the meantime, FA+ (NH2‐C=NH) and K+ cations can be well fixed by hydrogen bonding interaction between FA+ and BF4‐, and electrostatic attraction between sulfonyl oxygen and K+ ions, respectively. Thereby, FAPbI3 crystal grain sizes are increased, interfacial defects are significantly reduced and carrier extraction/transport is facilitated, leading to better cell performance and excellent stabilities. Non‐encapsulated devices can maintain 91% of their initial efficiency under maximum‐power‐point (MPP) tracking while continuous illumination (~100 mW cm‐2) for 1000 h, and retain 91% of the initial efficiency after 1000 h “double 60” damp‐heat stability testing (60°C and 60%RH (RH, relatively humidity)).