Advances in surface passivation of perovskites using organic halide salts for efficient and stable solar cells

Perovskite solar cells have shown tremendous progress in their efficiencies over a short time period. However, limitations such as defects and stability of perovskites have hindered their further progress. The major contributors that decrease the power conversion efficiency and open-circuit voltage of perovskite solar cells are the surface recombination of photoexcited charges and the degradation of absorber materials under different environmental conditions. Over the years, passivating the surface defects have been adopted to increase the charge carrier lifetime and reduce the surface traps thus increasing the charge collection efficiency at the electrodes. In particular, the use of organic halide salts to passivate perovskite surfaces have been studied extensively. The hydrophobicity of organic halide salts also aids in enhancing the moisture stability of perovskite solar cells. In this review, an overview of recent advances in organic halide salts for passivating perovskite surfaces is provided. Along with elucidating the influence of process parameters on surface defects, the importance of passivating the surface defects in perovskite materials is discussed. With greater emphasis on device parameters such as carrier lifetime, trap density and power conversion efficiency, the different organic halide salts used to enhance these parameters are individually described in detail. Further, a summary of device performance and stability of surface passivated perovskite solar cells is provided along with existing challenges.