Investigation of the Performance of Perovskite Solar Cells with ZnO-Covered PCBM Electron Transport Layer.

Due to its high carrier mobility and electron transmission, the phenyl-C-butyric acid methyl ester (PCBM) is usually used as an electron transport layer (ETL) in perovskite solar cell (PSC) configurations. However, PCBM films suffer from poor coverage on perovskite active layers because of their low solubility and weak adhesive ability. In this work, to overcome the above-mentioned shortcomings, 30 nm thick PCBM ETLs with different concentrations were modeled. Using a 30 nm thick PCBM ETL with a concentration of 50 mg/mL, the obtained performance values of the PSCs were as follows: an open-circuit voltage (V) of 0.87 V, a short-circuit current density (J) of 20.44 mA/cm, a fill factor (FF) of 70.52%, and a power conversion efficiency (PCE) of 12.54%. However, undesired fine cracks present on the PCBM surface degraded the performance of the resulting PSCs. To further improve performance, multiple different thicknesses of ZnO interface layers were deposited on the PCBM ETLs to release the fine cracks using a thermal evaporator. In addition to the pavement of fine cracks, the ZnO interface layer could also function as a hole-blocking layer due to its larger highest occupied molecular orbital (HOMO) energy level. Consequently, the PCE was improved to 14.62% by inserting a 20 nm thick ZnO interface layer in the PSCs.