Benzo[1,2-b:4,5-b′]difuran-based Narrow Bandgap Polymers for Efficient Organic Solar Cells Using Perylene Diimides-type Nonfullerene Acceptors

The development of narrow-bandgap polymer donors with complementary absorption and matched energy levels for perylene diimides (PDI)-based nonfullerene acceptors (NFAs) has received little attention. The high-lying highest occupied molecular orbital (HOMO) level and low degree of crystallinity of the star donor polymer PCE10 limit its application in PDI-based Organic solar cells (OSCs). In this study, two benzo[1,2-b:4,5-b′]difuran (BDF)-based narrow-bandgap polymer donors, PBDF and PBDFCl, were synthesized to improve the photovoltaic performance of PDI-based OSCs. The smaller BDF moiety with higher electronegativity endows the resulting polymers with stronger aggregation and lower HOMO energy levels. The power conversion efficiency (PCE) value of the PBDF:Ph(PDI)₃-based OSCs was 7.24%, which is much higher than that of PCE10-based OSCs (6.09%). Further chlorination of the conjugated side chain elevated the PCE to 8.84%, which is 1.4 times higher than that of PCE10-based OSCs. These results demonstrate the significant contribution of designing novel narrow-bandgap polymer donors to boost the PCE of PDI-based OSCs and highlight the importance of matching the aggregation behaviors of polymeric donor materials with that of NFAs.