Optimizing electron transport layers for high-efficiency perovskite solar cells using impedance spectroscopy

The best interface for a perovskite solar cell is designed to facilitate effective charge transport to achieve a high-power conversion efficiency. Tin dioxide (SnO₂) is widely recognized as an electron transport material for perovskite solar cells, offering advantages such as low hysteresis, low defect concentration, and low fabrication temperature. However, the low conduction band edge of SnO₂ restricts the built-in potential of the solar cell device. In this study, we designed a double layer of electron transport by applying zinc oxide (ZnO) on SnO₂ to improve the electron transport properties in perovskite solar cells. The bilayer of electron transport enhances the interfaces between the perovskite and the electron transport layer, leading to an improvement in the efficiency and stability of solar cell devices up to 11.71 % compared to a single SnO2 layer device with a PCE of 9.06 %. The introduction of ZnO reduces charge recombination, resulting in a lower recombination resistance (Rrec). Also, charge transfer resistance (Rct) of ZnO/SnO₂ increased to 16.6KΩ compared to a single SnO₂ layer device with a Rct of 5.29KΩ. Our findings provide valuable insights into the design of electron transport layers for perovskite solar cells and highlight the importance of electrochemical impedance spectroscopy in understanding the dynamic processes that govern their performance.