Cobalt Chloride Hexahydrate Assisted in Reducing Energy Loss in Perovskite Solar Cells with Record Open-Circuit Voltage of 1.20 V

Abstract

SnO2 is widely used and one of the most efficient electron transport layers in perovskite solar cells (PSCs). However, SnO2 films often contain detrimental defects and may also have mismatches in energy level alignment with perovskite films, thus limiting the open-circuit voltage (VOC). Managing the defects and band structure are critical to reduce energy loss in PSCs. Herein, cobalt chloride hexahydrate (CoCl2·6H2O) is introduced into a SnO2 film, which shows favorable energy level alignment and better charge extraction. Correspondingly, an enhanced VOC up to 1.20 V was achieved along with an efficiency of 23.82%, which is the record open-circuit voltage at the optical band gap of 1.54 eV in planar structure PSCs. Moreover, the target devices show enhanced stability, which retains 83.5% of their initial efficiencies after 200 h under continuous irradiation. The doping method provides an effective strategy for reducing energy loss to further enhance the efficiency of PSCs.