LAUSR

Abstract The electronic and structural properties of the four copolymers, PBDPQU, PBDPBT, PBDPDPP, and PBDPTP, are investigated by density functional theory and time-dependent density functional theory. The research purpose is to rationalize the relationship between observed experimental performances and structural properties. The properties that can affect open-circuit voltage (VOC) and short-circuit current (JSC) are comprehensively investigated, which refer to absorption spectra, frontier molecular orbital, charge transport properties, and exciton dissociation abilities at the copolymer/PCBM interface. The results indicate that the favourable photovoltaic performances of PBDPBT are due to large VOC, lower the highest occupied molecular orbital (HOMO), and small effective mass (m*). Furthermore, the unfavourable performance of PBDPTP mainly originates from the higher HOMO level and weak ability of exciton dissociation at interface, while the intermediate properties aforementioned for PBDPQU and PBDPDPP determine their intermediate photovoltaic performances. In conclusion, the theoretical results agree well with the experimental ones.