In Situ Defect Passivation with Silica Oligomer for Enhanced Performance and Stability of Perovskite Solar Cells

Perovskite solar cells (PVSCs) have achieved excellent power conversion efficiency (PCE) but still suffer from instability issues. Defect passivation is an important route to simultaneously increase the efficiency and stability of PVSCs. Here, a strategy of incorporating silica oligomer in perovskite films for surface and grain boundary defect passivation is reported. Silica oligomer passivation agent (PA) is in situ formed through hydrolysis and condensation reaction of tetraethyl orthosilicate additive in perovskite precursor. The passivation mechanism is elucidated by density functional theory calculation, revealing stable chelating interaction and hydrogen bond interaction between PA and perovskite. Spectroscopic and electrical characterizations demonstrate that silica oligomer can enlarge grain sizes, prolong carrier lifetime, enhance charge carrier dynamics, and reduce trap state densities in perovskite films. Planar PVSCs with passivation achieve a highly improved PCE of 19.64% with a stabilized efficiency of 18.81%. More importantly, unencapsulated perovskite devices with passivation retain nearly 90% of original efficiency after 1000 h storage under ambient condition and sustained 87% of initial performance after high-temperature (120 degrees C) thermal accelerated aging, showing highly enhanced moisture and thermal stability. Therefore, the present study provides a pathway to the future design and optimization of PVSCs with higher efficiency and greater stability.