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-ThCl15, and PBDB-Th2Cl15). Among these three polymers, PBDB-ThCl15 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-ThCl15:Y6-based device showed the highest PCE of 15.63% of the three polymers. The PBDB-Th15- and PBDB-Th2Cl15-based devices present relatively poor conversion efficiencies of 14.91% and 12.62%. Interestingly, the terpolymer PBDB-ThCl15 was repeatedly prepared by random terpolymerization under the same conditions, and a low batch-to-batch variation was observed with a PCE of ∼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.