Performance Enhancement of Evaporated CsPbI2Br Perovskite Solar Cells with a CuSCN Hole Transport Layer via a Cesium Bromide Buffer Layer

Copper(I) thiocyanate (CuSCN), which is an ideal hole transport material (HTM), can remedy the disadvantages of organic HTMs due to its high mobility, excellent durability, hydrophobic property, and low cost. However, diethyl sulfide as a polar solvent for dissolving CuSCN damages the surface of the CsPbI 2 Br perovskite during the deposition of CuSCN. With the introduction of an ultrathin CsBr buffer layer between the CsPbI 2 Br and CuSCN layers, the degradation of the CsPbI 2 Br absorber layer caused by diethyl sulfide could be reduced, and the CsBr buffer layer could also passivate the defects at the CsPbI 2 Br surface. By introducing a 6 nm thick CsBr buffer layer, the power conversion efficiency of the CsPbI 2 Br–CuSCN-based perovskite solar cell (PVSC) devices fabricated by vacuum evaporation deposition was enhanced from 1.84 to 9.96%, which was comparable to the performance (11.8%) of the evaporated CsPbI 2 Br PVSCs using organic HTMs. Our work provides a practicable strategy to elevate the performance of CsPbI 2 Br PVSCs.