Toward high efficiency of inverted organic solar cells : Concurrent improvement in optical and electrical properties of electron transport layers

The conversion efficiency (η) of organic solar cells (OSCs) constructed with ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag is improved by incorporating Al into ZnO films (AZO) as electron transport layers (ETLs). Compared with ZnO films, AZO-based OSCs enhance η by ∼13.9% via improving short-circuit photocurrent density from 10.73 to 11.12 mA cm^-2 and fill factor from 53.7% to 60.8%. Doping Al into ZnO ETLs not only optimizes band alignment between organic active layers and ETLs and increases carrier concentration, conductivity, and bandgap of ZnO films facilitating more light into OSCs but also improves the absorption of P3HT by promoting the molecular ordering of P3HT.