Suppressed Ion Migration in FA‐Rich Perovskite Photovoltaics through Enhanced Nucleation of Encapsulation Interface

Abstract With excellent homogeneity, compactness and controllable thickness, atomic layer deposition (ALD) technology is widely used in perovskite solar cells (PSCs). However, residual organic sources and undesired reactions pose serious challenges to device performance as well as stability. Here, ester groups of poly(ethylene‐co‐vinyl acetate) are introduced as a reaction medium to promote the nucleation and complete conversion of tetrakis(dimethylamino)tin(IV) (TDMA‐Sn). Through simulations and experiments, it is verified that ester groups as Lewis bases can coordinate with TDMA‐Sn to facilitate homogeneous deposition of ALD‐SnO_x, which acts as self‐encapsulated interface with blocking properties against external moisture as well as internal ion migration. Meanwhile, a comprehensive evaluation of the self‐encapsulated interface reveals that the energy level alignment is optimized to improve the carrier transport. Finally, the self‐encapsulated device obtains a champion photovoltaic conversion efficiency (PCE) of 22.06% and retains 85% of the initial PCE after being stored at 85 °C with relative humidity of 85% for more than 800 h.