BC-76 First-Principles Study of Structure and Electronic Properties of Cofacial Phenylene Vinylene Dimers for Organic Photovoltaic Cell Application

The development of efficient and sustainable energy sources has driven research into organic photovoltaics (OPVs), where polymers play a critical role as active materials. Polymer-related factors such as molecular structure and interaction, and band gap, restrict the efficiency of OPV devices, complicating the study of interactions between individual polymer chains. Their spatial orientations relative to one another are typically variable and often unknown. To address this problem in our phenylene vinylene dimers with xanthene and dibenzofuran bridging units, we conducted a first-principles study to investigate their structure, molecular and inter-polymeric chain interactions, and the electronic properties. These low bandgap cofacial polymers have potential applications in organic photovoltaic devices or solar cells. This study employed ground-state DFT and Time-Dependent TD-DFT calculations in both gas and solution phases to specifically explore the geometrical parameters, electronic excitations, and interchain electronic interactions of these polymers. Our findings revealed that there were two distinct absorption bands: a red-shifted band from those of the individual oligomers (stilbene and phenylene vinylene tetramer) due to the planarization of polymers in a constrained cofacial environment and a blue-shifted band (from those of individual oligomers) arising from excitonic coupling which was influenced by extended chain length and interchain distance. These properties further facilitate excitation localization on a single chain, driven by geometric relaxation and solvent reorganization. Furthermore, the structural and electronic properties of these polymers were compared with each other and with available experimental data. The details understanding obtained from this study will serve as a foundation for future experimental design and optimization of polymer-based organic photovoltaic devices or solar cells.