A Random Terpolymer Donor with Similar Monomers Enables 18.28% Efficiency Binary Organic Solar Cells with Well Polymer Batch Reproducibility

Herein, by using two fluorinated and chlorinated monomers with similar structures in different molar ratios and dithieno[3',2':3,4;2 '',3 '':5,6]benzo[1,2-c][1,2,5]thiadiazole (DTBT) as the third unit, a family of polymer donors D18, D18-20%Cl, D18-40%Cl, and D18-Cl are synthesized for OSCs. With appropriate chlorinated monomer proportion, the terpolymer D18-20%Cl exhibits proper HOMO energy level and higher packing density compared with that of other control polymers. Moreover, the D18-20%Cl:Y6 blend films have favorable morphology with better face-on crystallization and better charge transport. Consequently, the D18-20%Cl:Y6-based OSCs obtain a top-ranked PCE of 18.28% with overall improved device parameters compared to the controlled D18:Y6 or D18-Cl:Y6-based OSCs (17.50% or 17.02%), which represents the highest PCE for the reported terpolymer-based binary OSCs. Notably, the D18-20%Cl:Y6-based OSCs exhibit over 17% efficiency in a wide molecular weight range. These results demonstrate that the ternary copolymerization of DTBT and two similar moieties is an efficient approach for achieving efficient terpolymer donors with well batch-to-batch reproducibility.

Automated summary

In this study, a family of polymer donors for organic solar cells (OSCs) was synthesized using a ternary copolymerization approach. The terpolymer D18-20%Cl, with an appropriate proportion of chlorinated monomer, demonstrated the best performance with improved morphology and charge transport when blended with Y6. This resulted in a top-ranked power conversion efficiency (PCE) of 18.28% for D18-20%Cl:Y6-based OSCs, the highest reported PCE for terpolymer-based binary OSCs.