Investigation of the Performance of Perovskite Solar Cells with ZnO-Covered PC₆₁BM Electron Transport Layer

Due to its high carrier mobility and electron transmission, the phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) is usually used as an electron transport layer (ETL) in perovskite solar cell (PSC) configurations. However, PC₆₁BM 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 PC₆₁BM ETLs with different concentrations were modeled. Using a 30 nm thick PC₆₁BM ETL with a concentration of 50 mg/mL, the obtained performance values of the PSCs were as follows: an open-circuit voltage (V_oc) of 0.87 V, a short-circuit current density (J_sc) of 20.44 mA/cm², a fill factor (FF) of 70.52%, and a power conversion efficiency (PCE) of 12.54%. However, undesired fine cracks present on the PC₆₁BM surface degraded the performance of the resulting PSCs. To further improve performance, multiple different thicknesses of ZnO interface layers were deposited on the PC₆₁BM 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.