Effect of Molecular Structures of Donor Monomers of Polymers on Photovoltaic Properties.

This work investigates the photovoltaic properties of polymers that include different carbazole blocks as electron donors (D) but the same benzothiadiazole derivative as the electron acceptor (A). Five D-A copolymers are studied with ultrafast intramolecular exciton splitting and recombination dynamics to acquire the single-molecule structure and their photovoltaic performance relationship. The photovoltaic parameters such as energy level, optical band gap, and light-harvesting ability are highly dependent on the molecular structure of the donor monomer (including their appended flexible alkyl chain). Branched or linear alkyl groups on the same D block obviously vary the polymer steady-state absorption spectra and film morphology. For organic solar cells, this work allows tuning and control of the ultrafast dynamics, implying photovoltaic material design in the future.