Multifunctional Interface Modification Enables Efficient and Stable HTL‐Free Carbon‐Electroded CsPbI₂Br Perovskite Solar Cells

In recent years, hole transport layer‐free all‐inorganic CsPbI 2 Br carbon‐electroded perovskite solar cells (C‐PSCs) have garnered significant attention due to a trade‐off between stability and photovoltaic performance. However, there are inevitably many defects generated at the surfaces or grain boundaries of CsPbI 2 Br perovskite films, which will serve as carrier non‐radiative recombination centers, and CsPbI 2 Br perovskite films are sensitive to water molecules to degrade, together with energy level mismatch between CsPbI 2 Br perovskite and carbon electrodes. Herein, 1‐benzyl‐3‐methylimidazolium hexafluorophosphate (1‐B‐3‐MIMPF 6 ), an imidazolium‐based ionic liquid simultaneously containing benzene ring and fluorine atoms, was introduced for the modification of the perovskite/carbon interface. The results showed that it could effectively reduce defects, enhance carrier transfer, mitigate carrier non‐radiative recombination, facilitate energy alignment, and block moisture intrusion. Therefore, the photovoltaic performance of the modified PSCs with ITO/SnO 2 /CsPbI 2 Br/1‐B‐3‐MIMPF 6 /carbon architecture has been boosted with a champion power conversion efficiency (PCE) of 13.47 %, open circuit voltage of 1.20 V, short circuit current density of 14.69 mA/cm 2 , and fill factor of 76 %. Moreover, the unencapsulated modified devices exhibited an improved stability and the PCE maintained 78 % of their initial PCE after 24 h storage at room temperature in a 30 %–35 % humidity environment, whereas that of the pristine devices dropped to almost zero.