Surface Management for Carbon‐Based CsPbI 2 Br Perovskite Solar Cell with 14% Power Conversion Efficiency

Carbon‐based hole transport material (HTM)‐free CsPbI 2 Br perovskite solar cells (C‐PSCs) have garnered considerable attention due to their super thermal stability. The energy‐level mismatch between the CsPbI 2 Br perovskite and carbon electrodes, however, results in major energy loss and reduced power conversion efficiency (PCE) of C‐PSCs. Herein, 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF 4 ) is used to manage the energy level, reduce defect densities, and improve the interface quality between CsPbI 2 Br and carbon electrodes. Preliminary results demonstrate that the BMIMBF 4 modifier can passivate the surface defects of the perovskite film and reduce the energy‐level mismatch between the CsPbI 2 Br layer and the carbon electrode. A PCE of 14.03% is achieved by introducing BMIMBF 4 which is improved by 23% compared with the control device (11.37%). Moreover, stability—whether in the case of C‐PSCs or CsPbI 2 Br films—is also improved.