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.