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

In recent years, hole transport layer-free all-inorganic CsPbI₂Br 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 CsPbI₂Br perovskite films, which will serve as carrier non-radiative recombination centers, and CsPbI₂Br perovskite films are sensitive to water molecules to degrade, together with energy level mismatch between CsPbI₂Br perovskite and carbon electrodes. Herein, 1-benzyl-3-methylimidazolium hexafluorophosphate (1-B-3-MIMPF₆), 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/SnO₂/CsPbI₂Br/1-B-3-MIMPF₆/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/cm², 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.