In recent years, organic photovoltaic devices have been a great attention due to their advantages such as low costs, light weight, flexibility, and short energy payback time. There have been many efforts to improve the power conversion efficiency and device stability such as the synthesis of functional materials, design of unique device architectures and morphology control. In spite of these efforts, further improvements in device performance are required for commercial applications.For high performance photovoltaics, photo-carriers should be generated efficiently and the generated carriers should be extracted to electrodes without loss. One strategy to improve the charge generation is the development of narrow band gap materials. Push-pull molecules have shown efficient charge generation with their broad solar absorption spectra. However, even devices with excellent absorption could show low performance due to the poor charge extraction property. The charge extraction barrier at the electrode interface is of critical importance for the charge extraction, which impedes the charge transport from an active layer and to electrodes.The charge extraction barrier is determined by the interfacial electronic structure at the active layer/electrode interface and it can be measured properly with photoelectron spectroscopy. In this work, it will be investigated that the charge extraction mechanism in photovoltaics by measuring the interfacial electronic structure between active layer and electrode. Ultraviolet photoelectron spectroscopy and inverse photoelectron spectroscopy measurements will be conducted for the active layer of narrow band gap molecule ditolylaminothienyl–benzothiadiazole–dicyanovinylene (DTDCTB) and the charge extraction layer of Ba(OH)2 and DNA base cytosine.