Defect Passivation with Organic Co‐Crystal Layers for Efficient and Stable Inverted Perovskite Solar Cells: A Non‐2D‐Perovskites Strategy for Surface Treatments

ABSTRACT Surface defects caused by the wet‐chemical deposition method negatively affect the performance and stability of inverted perovskite solar cells (PSCs). It is common to post treat perovskite films with large‐sized organic ammonium salts, which allow for the formation of 2D perovskites on top of the perovskite films. However, the low‐dimensional perovskites feature a low charge carrier mobility and poor structural stability. To address these issues, we introduce an organic co‐crystal layer rather than 2D perovskites on top of the perovskite film in this work. This co‐crystal layer effectively passivates the surface defects through a reinforced hydrogen‐bonding network, suppresses non‐radiative recombination, enhances n‐type semiconductor characteristics, increases electron mobility and facilitates charge carrier transport in the perovskite films. As a result, the PSCs based on this layer achieve a champion power conversion efficiency (PCE) of 26.35% with enhanced short‐circuit current ( J SC ) and open circuit voltage ( V OC ). Furthermore, the nonencapsulated device exhibits excellent thermal and moisture‐resisted stability, manifesting in 80% initial PCE retention under heat stress of 85°C for 1392 h and 88% initial PCE retention after exposure to air with ∼50% RH for 2040 h. This work provides a novel strategy to passivate the surface defects of perovskite films beyond the formation of 2D perovskites for inverted PSCs.