Ion diffusion-induced double layer doping toward stable and efficient perovskite solar cells

The perovskite layer, electron transport layer (ETL) and their interface are closely associated with carrier transport and extraction, which possess a pronounced effect on current density. Consequently, the dissatisfactory electric properties of functional layers pose a serious challenge for maximizing the thermodynamic potential of current density of perovskite solar cells (PSCs). Herein, we report an ion diffusion-induced double layer doping strategy for efficient and stable PSCs, where LiOH is directly added into SnO2 colloidal dispersion solution. It is uncovered that a small amount of Li+ ions remain in the ETL and doped SnO2 while a large amount of Li+ ions diffuse to SnO2/perovskite interface and into perovskite layer and gradient concentration distribution is spontaneously formed. The Li+ ion doping endows both perovskite and SnO2 layers improved electric properties, which contributes to facilitated carrier transport and extraction. Moreover, the crystallinity and grain size of perovskite films are enhanced after doping. The doped device delivers a higher power conversion efficiency (PCE) of 21.31% together with improved ambient stability in comparison with the control device (PCE = 19.26%). This work demonstrates a simple and effective ion diffusion-induced double layer by chemical doping strategy to advance the development of perovskite photovoltaics.