Self-Formation of SnCl2 Passivation Layer on SnO2 Electron-Transport Layer in Chloride–Iodide-Based Perovskite Solar Cell

The phenomenon of the self-formation of a passivation layer at the interface of the perovskite/electron-transport layer (ETL) is observed. FA_0.6MA_0.4PbI_3−xCl_x perovskite thin film is deposited on a SnO₂ nanoparticle thin-film ETL. It is observed from the depth-resolved spectroscopy that the Sn²⁺ ion migrates toward the perovskite layer within the ETL. At the same time, Cl⁻ ion also migrates toward ETL within the perovskite layer. This unique ion migration phenomenon leads us to conclude that a passivating SnCl₂ layer is formed at the perovskite/ETL interface. It is found that this SnCl₂ layer at the interface works as a passivation layer like Al₂O₃. There is a significant effect of this self-formed passivating layer behind the improvement of the device's efficiency and stability. It is believed that this SnCl₂ passivation layer helps to reduce the recombination loss at the interface and boosts the performance of the perovskite solar cell (PSC). The perovskite/hole-transport layer is also passivated with octylammonium bromide. Finally, the PSC offers a photoconversion efficiency (PCE) of 20.81% under 1 sun and AM1.5 G condition. Again, it maintains more than 80% of PCE under open-air room conditions, white light emitting diode, and 85 °C continuous heating for more than 12 h without encapsulation.