Optimizing Vertical Crystallization for Efficient Perovskite Solar Cells by Buried Composite Layers

Planar‐heterojunction perovskite solar cells (PSCs) have experienced rapid evolution in recent years because of the low‐temperature processing, suitable alignment, and high mobility of the tin oxide buried contact layer. However, improper SnO 2 surface states and poor crystallinity of the top perovskite films are still the main obstacles for the planar PSCs in which performance always lags behind their mesoporous counterparts. Herein, a new buried contact is reported by introducing graphitic carbon nitride (g‐C 3 N 4 ) into the commonly used SnO 2 which performs outstanding transmittance, conductivity, and surface states for a high‐quality electron‐transporting layer. Moreover, the vertical composition and crystallinity of the top perovskite film are manipulated by rich amino groups on the edge of the g‐C 3 N 4 nanosheets which induce the prenucleation of the lead‐rich species at the buried interface. Benefiting from the high‐quality buried contacts and the optimized perovskite layers, the resultant PSCs achieve a champion efficiency of 21.5% with all photovoltaic parameters enhanced in comparison with their control counterparts (<20%).