Energetic Alignment-Related Effect on Carrier Extraction in Organic Photovoltaic Devices with Cathode Conducting Layer

The performance of organic photovoltaic (OPV) devices is strongly dependent on the electronic structure at the interface, including energetic offset induced by the electronic coupling of the materials and how the materials link to each other. Herein, the studies on modification of the interface of active layer and cathodes with insertion of carrier selective materials are reported. The thermalization of hot metal diffusion via X-ray photoemission spectroscopy (XPS) as well as the energetic offset via ultraviolet photoemission spectroscopy (UPS) in situ is characterized. These investigations allow them to investigate the mechanisms at the interface and correlate these findings with the device performance, such as the correlation between interfacial energy band alignment and charge carrier transport, recombination, and extraction. Finally, the influence of cathode modification materials with various energetic offsets or transport behaviors on V_oc and OPV performance parameters is investigated. With these studies, it is suggested that the incorporation of electrode modification materials with energetic favorable band alignment can achieve better photovoltaic performance.