Annealing Effect of ZnO on the Performance of Inverted Organic Photovoltaic Devices

ZnO nanoparticles films were prepared via sol-gel process and incorporated into inverted organic photovoltaic devices with a structure of ITO/ZnO/P3HT:PCBM/MoO3/Ag, in which ZnO film served as an electron selective layer. The effects of annealing temperature of ZnO film on the device performance were investigated. When the annealing temperature was 300 °C, a well-arranged ZnO thin film was obtained, and the optimized device had doubled short circuit current density (JSC) and seven-fold higher power conversion efficiency (PCE) compared to the devices without ZnO film. This improvement could be attributed to the enlarged interfacial area of ZnO/active layer and better energy band matching which causes an efficient electron extraction and a decreased interface energy barrier. At particularly high annealing temperature, dramatically increased sheet resistance of indium tin oxide (ITO) was found to cause PCE deterioration. Our finding indicates that it is highly important to investigate both morphology and electrical effects for understanding and optimizing organic photovoltaic (OPV) performance.