Sodium fluoride sacrificing layer concept enables high-efficiency and stable methylammonium lead iodide perovskite solar cells

Abstract

• A new NaF sacrificing layer is introduced into the TiO 2 ETL/perovskite interface. • NaF is partially incorporated into mesoporous TiO 2 ETL to reduce its defect amount and photocatalytic activity. • The introduction of NaF into the ETL constructs a well-matched energy level alignment. • NaF is partially penetrated into the perovskite layer to improve the film quality. • The device with NaF sacrificing layer displays a high PCE of 20.9% with enhanced moisture/thermal/sunlight stability. As next-generation photovoltaic devices, methylammonium lead iodide (MAPbI 3 )-based organic-inorganic halide perovskite solar cells (PSCs) have received considerable attention because of their cost effectiveness and high efficiency. However, their practical applications are retarded due to severe instability under moisture, thermal and sunlight conditions, which are closely related to the insufficient perovskite film quality and high photocatalytic activity of defective TiO 2 electron-transporting layer (ETL) to accelerate the perovskite decomposition. Herein, remarkably enhanced power conversion efficiency (PCE) and stability of MAPbI 3 -based PSCs is reached through the use of a new sodium fluoride (NaF) sacrificing layer, which, introduced between the perovskite layer and ETL, is sacrificed during cell fabrication by penetrating into the perovskite layer, improving the perovskite film quality, while partial NaF is incorporated into the mesoporous TiO 2 ETL during NaF layer fabrication to passivate TiO 2 and construct a well-matched energy level alignment. As a result, the optimized PSC generates a high PCE of 20.9%, which is 17% higher than that of the pristine cell (17.9%), and outstanding performance stability due to remarkably enhanced moisture, thermal and sunlight stability. This study highlights a simple and effective approach to boost the PCE and durability of MAPbI 3 -based PSCs simultaneously, accelerating the commercialization of this technology.