Three‐Dimensional (3D) 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 trifluoromethane-sulfonamide (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=NH₂ ⁺) 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 while carrier extraction/ transportation 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)).