Enhanced efficiency of organic solar cells by using a ZnO-Fe2O3 electron transport layer

In this study, a ZnO-Fe2O3 thin film was designed as electron transport layer for organic solar cells (OSCs). The preparation strategy was based on the spin coating of aqueous sol–gel precursor. The result showed that composite ZnO-Fe2O3-based OSCs had higher power conversion efficiency than pure ZnO-based OSCs. To explain this result, morphology, optical and physical properties of ZnO-Fe2O3 were investigated to analyze the relation between structure of interface layer and performance of OSCs. It was demonstrated that composite ZnO-Fe2O3 layer had denser structure and lower surface roughness than pure ZnO layer. Thus, it showed a good contact with the active layer. Furthermore, 3.3% Fe2O3 could reduce the WF and Eg of ZnO, and greatly enhanced electron mobility from the acceptor (IT-4F) phase to the ZnO/ITO electrode. Meanwhile, ZnO-Fe2O3 layer showed a low reflectivity that allowed more photons to entrance the active layer for utilization. Hence, the higher short-circuit current and power conversion efficiency were achieved in ZnO-Fe2O3-based OSCs.