In situ passivation of the buried interface in perovskite solar cells using a SnO2–PACl composite electron transport layer

Electron extraction and transport represent the fundamental functions of the electron transport layer (ETL) in perovskite solar cells (PSCs). In this work, a novel ETL precursor integrates n-propylamine hydrochloride (PACl) with tin oxide (SnO₂), which significantly enhances the electron extraction efficiency and provides in situ passivation for both SnO₂ and perovskite materials. The interaction between deprotonated PA⁰ and surface hydroxyl (–OH) groups on SnO₂ nanoparticles reduces the density of dangling bonds, thereby decreasing non-radiative recombination losses and improving the electron extraction efficiency of the ETL. Moreover, during the annealing process, the PACl additive partially penetrates the perovskite layer, effectively slowing the crystallization rate, promoting grain growth, and improving the overall quality of the perovskite films. As a result, the power conversion efficiency (PCE) of the modified device increases to 24.39%, compared to 23.55% for the unmodified device. This improvement is primarily attributed to an enhancement in the device's fill factor, with the champion device achieving a fill factor of up to 83.44%. In comparison with conventional interface modification techniques, the composite ETL strategy proposed in this study provides a promising pathway for defect passivation, thereby enabling further efficiency improvements in PSCs.