Terpolymerization and Regioisomerization Strategy to Construct Efficient Terpolymer Donors Enabling High-Performance Organic Solar Cells

Terpolymerization and regioisomerization strategies are combined to develop novel polymer donors to overcome the difficulty of improving organic solar cells (OSCs) performance. Two novel isomeric units, bis(2-hexyldecyl)-2,5-bis(4-chlorothiophen-2-yl)thieno[3,2-b]thiophene-3,6-dicarboxylate (TTO) and bis(2-hexyldecyl) 2,5-bis(3-chlorothiophen-2-yl)thieno[3,2-b]thiophene-3,6-dicarboxylate (TTI), are obtained and incorporated into the PM6 backbone via random copolymerization to form a series of terpolymers. Interestingly, it is found that different chlorine (Cl) substituent positions can significantly change the molecular planarity and electrostatic potential (ESP) owing to the steric hindrance effect of the heavy Cl atom, which leads to different molecular aggregation behaviors and miscibility between the donor and acceptor. The TTO unit features a higher number of multiple S center dot center dot center dot O non-covalent interactions, more positive ESP, and fewer isomer structures than TTI. As a result, the terpolymer PM6-TTO-10 exhibits a much better molecular coplanarity, stronger crystallinity, more obvious aggregation behavior, and proper phase separation in the blend film, which are conducive to more efficient exciton dissociation and charge transfer. Consequently, the PM6-TTO-10:BTP-eC9-based OSCs achieve a champion power conversion efficiency of 18.37% with an outstanding fill factor of 79.97%, which are among the highest values reported for terpolymer-based OSCs. This work demonstrates that terpolymerization combined with Cl regioisomerization is an efficient approach for achieving high-performance polymer donors.

Automated summary

Terpolymerization and regioisomerization strategies are utilized to develop novel polymer donors for improving the performance of organic solar cells (OSCs). The study shows that the position of chlorine substituents significantly affects the molecular planarity and electrostatic potential (ESP), thereby influencing the aggregation behavior and miscibility of the donor and acceptor. The terpolymer PM6-TTO-10 exhibits enhanced coplanarity, crystallinity, aggregation behavior, and phase separation, leading to efficient exciton dissociation and charge transfer. Consequently, OSCs based on PM6-TTO-10 achieve a high power conversion efficiency of 18.37% with an outstanding fill factor of 79.97%, which are among the highest reported for terpolymer-based OSCs.