Three‐Dimensional (3D) Fluoride Molecular Glue to Improve the SnO2/Perovskite Interface for Efficient Perovskite Solar Cells

Abstract Aiming at numerous defects at SnO 2 /perovskite interface and lattice mismatch in perovskite solar cells (PSCs), we design a kind of three‐dimensional (3D) molecular glue (KBF 4 ‐TFMSA), which is derived from strong intramolecular hydrogen bonding interaction between potassium tetrafluoroborate (KBF 4 ) 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 cm 2 device is also obtained. Further investigation reveals that this KBF 4 ‐TFMSA can interact with oxygen vacancies and under‐coordinated Sn(IV) from the SnO 2 , in the meantime, FA + (NH 2 −C=NH 2 + ) and K + cations can be well fixed by hydrogen bonding interaction between FA + and BF 4 − , and electrostatic attraction between sulfonyl oxygen and K + ions, respectively. Thereby, FAPbI 3 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)).