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 0.6 MA 0.4 PbI 3− x Cl x perovskite thin film is deposited on a SnO 2 nanoparticle thin‐film ETL. It is observed from the depth‐resolved spectroscopy that the Sn 2+ 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 SnCl 2 layer is formed at the perovskite/ETL interface. It is found that this SnCl 2 layer at the interface works as a passivation layer like Al 2 O 3 . 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 SnCl 2 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.