Interface Energetics And Morphology Of Organic Photovoltaic Devices

With the advancement of modern science and technology, organic optoelectronic devices including organic photovoltaic devices(OPV) and organic light-emitting devices(OLED) emerged and developed rapidly. Because of the advantages of low cost, easy fabrication and flexibility, nowadays OPV and OLED show a broad application prospect in fields such as development and utilization of new energy, new lighting, panel and flexible display technology. In order to realize further enhancement in the performance of organic optoelectronic devices, it is crucial to elucidate interface formation of such devices.In this thesis, we carried out the research on the influence of three factors on interface formation in polymer solar cells:(i) substrate materials,(ii) mixing ratio of donor and acceptor in the active layer and(iii) annealing temperature. The experimental methods have been ultraviolet photoelectron spectroscopy(UPS), X-ray photoelectron spectroscopy(XPS) and atomic force microscope(AFM). In such a way, we unravel the role of substrates and annealing on interface energetics and morphology. We brought PCDTBT:PC70BM blends in contact with four different substrates, namely Cs F, ZnO, PEDOT:PSS and MoO3, where the PCDTBT:PC70BM blend serves as an important model system due to efficient charge generation and transport with low recombination. The energetics of the PCDTBT:PC70BM blend film is demonstrated to be highly dependent on the substrate work function, showing the transition from vacuum level alignment to Fermi level pinning with the variation of PC70 BM ratio in the blend film.For the film morphology, phase separation is observed showing the formation of a PCDTBT-rich layer at the top of the PCDTBT:PC70BM blend film. Moreover, phase separation is also demonstrated by XPS and in accordance with UPS results. The results show the possibility of tuning the interfacial electronic structures by utilizing the substrate effects and potential applications on performance enhancement in polymer solar cells.