Defect Passivation by Fullerene Derivative in Perovskite Solar Cells with Aluminum-Doped Zinc Oxide as Electron Transporting Layer

ZnO is a potential replacement for TiO2 as an electron transport layer (ETL) used in low-temperature processed hybrid perovskite solar cells. However, poor thermal stability of perovskites on ZnO and interfacial traps introduced during processing are obstacles to achieve a good device performance. Here, we demonstrate perovskite solar cells using aluminum doped zinc oxide (AZO) nanoparticles for the ETL having a better thermal stability compared with ZnO. However, the device shows a lower short circuit current density and a large photocurrent hysteresis, which are attributed to the poor interfacial properties between the ETL and the perovskite layer. To address this issue, a thin interfacial modification layer of phenyl-C61-butyric acid methyl ester (PCBM) was employed. The resulting device shows the efficiency is improved from 13 to 17% along with a significant reduction in hysteresis. Results from our thermal admittance spectroscopy show that the interface defect states are significantly reduced with the PCBM passivation layer.