Wide Bandgap Polymer Donors Containing Dihalovinyl Thiophene Building Blocks for Organic Solar Cells

This work presents the development of two novel gem-dihalovinyl thiophene-based building blocks, namely 3-(2,2-difluorovinyl)thiophene (TDF) and 3-(2,2-dichlorovinyl)thiophene (TDCl), for constructing cost-effective wide bandgap polymer donors for organic solar cells (OSCs) based on narrow bandgap nonfullerene acceptors (NFAs). Two polymers, PBDT-TDF and PBDT-TDCl, have been synthesized using these building blocks. Both polymers have energy levels that match the NFA Y6. The OSC device with PBDT-TDF:Y6 has achieved a power conversion efficiency (PCE) of 8.83%. In contrast, the PBDT-TDCl:Y6-based device has a higher PCE of 11.02% due to the increased short-circuit current density. The improved charge transport ability in the PBDT-TDCl:Y6 blend film plays a vital role in enhancing the overall solar cell performance. An interesting observation is that the bulkier dichlorovinyl moiety seems to induce a conformational locking effect, effectively maintaining a higher extent of coplanarity in the polymer backbone. This effect contributes to the elevated hole mobility observed in PBDT-TDCl, in comparison to PBDT-TDF. These findings highlight the promising potential of these gem-dihalovinyl thiophenes as cost-effective building blocks for the growth of polymer semiconductors for solar cells and other printed electronics utilization.