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. FA0.6MA0.4PbI3−xClx 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.