Synthesis, characterization, DFT and TD-DFT studies of novel carbazole-based copolymer used in high efficient dye-sensitized solar cells

New donor-acceptor based copolymer incorporating carbazole as electron donor molecule and benzothiazole as electron withdrawing one has been designed and synthesized for organic solar cells applications. The synthesis procedure was achieved via a chemical oxydation pathway. Structural modifications were examined using infrared spectroscopy. Then, optical properties were investigated by the means of UV-VIS and photoluminescence measurements. A large red shift was observed in both optical absorption and emission spectra, showing an extension of the conjugation length going from the pristine PVK to the PVK-based copolymer. The experimental analyses were completed by theoretical calculations based on density functional theory (DFT) and time-dependant density functional theory (TD-DFT) methods. Then, Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) levels have been calculated in order to elucidate the intramolecular charge transfer (ICT) between the electron acceptor and the electron donor moieties and to establish the energetic diagrams of PVK and the PVK-based copolymer. All results showed that this copolymer exhibit interesting photophysical properties and shows promising photovoltaic trends.