Chlorinated Random Terpolymers with Efficient Solar Conversion and Low Batch-to-Batch Variation

The strategy of random terpolymerization has been shown to be a flexible and effective method with which to construct state-of-the-art polymer donors, and chlorination has frequently been utilized to fine-tune material properties in these polymers with the aim of improving the solar conversion efficiency. Herein, three random terpolymers consisting of BDT, BDD, and Th-Cl monomers in the optimized ratio of 1:0.85:0.15 were synthesized in parallel in an effort to understand the effect of chlorination in terpolymer systems and the chlorine-containing derviatives (named PBDB-Th15, PBDB-ThCI15, and PBDB-Th2CI15). Among these three polymers, PBDB-ThCI15 shows a low-lying HOMO level, the most balanced hole and electron mobility, and enhanced aggregation behavior in blend film as a result of the introduction of one chlorine atom. When blended with a small molecule accepetor Y6, the resulting PBDB-ThCI15:Y6-based device showed the highest PCE of 15.63% of the three polymers. The PBDB-Th15- and PBDB-Th2CI15-based devices present relatively poor conversion efficiencies of 14.91% and 12.62%. Interestingly, the terpolymer PBDB-ThCI15 was repeatedly prepared by random terpolymerization under the same conditions, and a low batch-to-batch variation was observed with a PCE of similar to 15.50%. These results indicate that the synergy of chlorination with random terpolymerization promises to contribute to the preparation of stable and high-performance solar cell polymers.