Application Of Interface Modification Layers Based On Zinc Oxide In Organic Solar Cells

Organic solar cells have been a hot research direction due to their promising advantagessuch as low-cost, flexibility and lightweight compared with the conventional silicon-basedsolar cells. In recent years, with the development of new materials and advanced processingtechniques flocking in, the power conversion efficiency of the device have been improvedrapidly and reached to10%in lab reports. However, the conventional solar cells influence thelong time stability of the photovoltaic devices because of the etching of the Indium tin oxide(ITO) by the acidic PEDOT:PSS and oxidation of the air-sensitive, low-work-function metalAl electrode. So the inverted organic solar cells have been exploited by the researchers. Inaddition to the high-work-function Ag, Au electrodes and the photoactive layer, the cathodebuffer layer between ITO electrode and photoactive layer also plays an important role ininfluencing the device performance of organic solar cells.Among the many cathode interfacial materials, ZnO has drawn much attention as thebuffer layer due to their advantages such as good transparency, environmental stability,simplicity of process and low crystallization temperature. However, the ZnO NPs filmpresents apparent surface defects due to aggregations, leading to poor interfacial contact withthe active layer and thus severe back charge recombination. Therefore, the main content ofthis thesis is interface modification of ZnO buffer layer through the three different methods.(1). The blend buffer layer is obtained by the blend of ZnO nanoparticles and TiO2nanorods. Compared to the respective single-component buffer layer, the blend buffer laterhas preferable interface contact with active layer, reducing the contact resistance and leakagecurrent. Meanwhile, the ZnO nanoparticles increase the contact area with the active layer, andthe TiO2nanorods provide the directed path for electron transport. Thus, the blend bufferlayer improves the electron transport and collection efficiency, resulting that the best powerconversion efficiency of the device based on the blend buffer layer reaches8.82%.(2). The ZnO/PyC60double interface layer is provided by the interfacial modification ofZnO buffer layer with the C60pyrrolidine tris-acid ethyl ester (PyC60). The intercalation ofPyC60reduces surface defects of ZnO buffer layer, improves the interface contact quality withactive layer and also lowers the electron injection barrier between photoactive layer and ZnObuffer layer, which increase the electron collection efficiency and decrease leakage currentconsequently. The power conversion efficiency of the device achieves8.76%.(3). The aggregations of ZnO nanoparticles in solution can be reduced by adjusting theratios of mixed solvent (chloroform and methanol), which obtain the lower roughness, compact and homogeneous ZnO film. The preferable ZnO buffer layer decrease leakagecurrent and improve interface contact quality with the active layer, increasing the powerconversion efficiency of device based on single-component ZnO film as cathode buffer layer(8.58%).