Identification and Mitigation of a Critical Interfacial Instability in Perovskite Solar Cells Employing Copper Thiocyanate Hole‐Transporter

Metal halide perovskites have emerged as one of the most promising materials for photovoltaic solar cells, with power conversion efficiency of over 22% already been demonstrated. In order to compete with traditional crystalline solar cells, cost and stability are the two most important issues that need to be considered besides efficiency. Here a 13.3% efficient perovskite solar cell with spray coated CuSCN is reported as hole transporting material (HTM) in regular, n-i-p solar cell structure. The relatively smooth spray coated CuSCN film can provide very reproducible solar cell performance. The stability of cells employing CuSCN is then compared with those employing the archetypical organic HTM, under elevated temperatures in ambient atmosphere. It is found that the devices employing spray coated CuSCN appear to intrinsically facilitate the degradation of perovskite films. By including a thin mesoporous alumina (Al2O3) “buffer layer” directly on top of the perovskite, followed by CuSCN and an additional coating of insulating poly(methyl methacrylate) on top of the CuSCN, this degradation is inhibited, and perovskite solar cells are delivered which survive for more than 1000 h at 85 °C in air.