Alkali metal ions passivation to decrease interface defects of perovskite solar cells

Charge carrier recombination occurring in the interface has become a major hindrance impairing the efficiency and stability of perovskite solar cells (PSCs). Passivation of electronic defects at the surface and grain boundaries is one of the most important strategies to suppress charge recombination and improve crystallization in PSCs. Herein, sodium sulfate (Na2SO4) passivation layer was incorporated into the TiO2/perovskite interface to improve charge transfer. Compared to the devices without Na2SO4, the device with the optimized concentration of Na2SO4 solution exhibits an increased short-circuit current density of 22.83 mA/cm2 and an enhanced fill factor of 73.68%, yielding an increased power conversion efficiency from 15.20% to 18.75%. The efficiency improvement is attributed to the decreased defects and traps as well as the enhanced film crystallization quality.