Comparative study of cesium halide (CsX, X = I, Cl, Br) modifications on defect passivation in tin-based perovskite solar cells

Tin-based perovskite solar cells are expected to replace lead-based perovskite solar cells to achieve environmentally friendly devices. Currently, a significant challenge lies in low filling factor and short-circuit current density, leading to an overall lower efficiency of these cells. In this context, we conducted a comprehensive comparative study on the deposition of these three inorganic small-molecule materials (CsBr, CsCl, CsI) on tin-based perovskite layers. The results showed that depositing these three inorganic small-molecule materials (CsBr, CsCl, CsI) on tin-based perovskite layers can improve the topography of the thin film and display an increased grain size. Simultaneously, the presence of the passivation layer facilitates preferred crystal orientation and enhanced charge carrier transport capabilities. Furthermore, devices with passivation layers exhibit reduced series resistance and increased shunt resistance, leading to a higher filling factor, a higher short-circuit current density, and a reduced leakage current in the passivated devices. This results in an elevated overall conversion efficiency of the devices. Notably, among the three halide materials employed for passivation, CsI demonstrates the most effective passivation, with the champion device achieving an efficiency of 6.0%. This study contributes valuable insights into the passivation strategies for tin-based perovskite solar cells.