Spatially Selective Molecular Engineering for Multiscale Defect Mitigation in Perovskite Photovoltaics

Perovskite solar cells (PSCs) have achieved remarkable progress through suppressing nonradiative recombination via surface and bulk treatment. However, randomly integrating surface and bulk treatments mutually interfere with their functions, limiting the superposed efficacy in defect mitigation. Herein, we present a spatially complementary multiscale defect-management strategy through the selective integration of cesium trifluoroacetate (CsTFA) additives with phenethylammonium bromide (PEABr) surface treatments. Driven by top-down crystallization of perovskite films, CsTFA preferentially migrates to the bottom region of the perovskite film, eliminating the unexpected interference with the top surface ligands. CsTFA suppresses bulk defects through Pb2+-carbonyl coordination and hydrogen bonding, while a formed two-dimensional (PEA)2PbI4 top capping layer terminates the surface dangling bonds. This synergistic strategy yields perovskite films with reduced defects and extended carrier lifetimes. The optimized devices demonstrate the power conversion efficiency (PCE) of 25.84% with enhanced stability, maintaining 84.46% of the initial efficiency under ambient conditions for 2000 h.