Random Copolymerization Strategy for Host Polymer Donor PM6 Enables Improved Efficiency Both in Binary and Ternary Organic Solar Cells

Abstract Although breakthroughs have been made in organic solar cells (OSCs) in recent years, the power conversion efficiency (PCE) of OSCs still lags behind inorganic/perovskite solar cells. In this work, two terpolymers were synthesized by introducing the thieno[3,4‐ c ]pyrrole‐4,6‐(5 H )‐dione (TPD) block into the host polymer donor PM6. Owing to the lower highest occupied molecular orbital energy level, wider light absorption, optimal molecular packing, and more desirable aggregation morphology by addition of the TPD, the PM6‐TPD‐5 % : Y6‐based device displayed an improved PCE of 16.3 % with an enhanced open‐circuit voltage ( V OC ) of 0.860 V, relative to that of PM6‐TPD‐10 % : Y6 (PCE=14.8 %) and PM6 : Y6‐based device (PCE=15.6 %). Interestingly, the V OC did not always increase in proportion to the third component. Besides, ternary OSCs based on PM6 : PM6‐TPD‐5 % : Y6 achieved a superior PCE of 17.1 %. This work demonstrated that random copolymerization is a feasible and effective strategy to further increase device performance, and the two polymers that possess similar structure and absorption in ternary devices can also obtain impressive efficiency.