Optimized Active Layer Morphologies via Ternary Copolymerization of Polymer Donors for 17.6 % Efficiency Organic Solar cells with Enhanced Fill Factor

Regulating molecular structure to optimize the active layer morphology is of considerable significance for improving the power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, we demonstrated a simple ternary copolymerization approach to develop a terpolymer donor PM6-Tz20 by incorporating the 5,5 '-dithienyl-2,2 '-bithiazole (DTBTz, 20 mol%) unit into the backbone of PM6 (PM6-Tz00). This method can effectively tailor the molecular orientation and aggregation of the polymer, and then optimize the active layer morphology and the corresponding physical processes of devices, ultimately boosting FF and then PCE. Hence, the PM6-Tz20: Y6-based OSCs achieved a PCE of up to 17.1% with a significantly enhanced FF of 0.77. Using Ag (220 nm) instead of Al (100 nm) as cathode, the champion PCE was further improved to 17.6%. This work provides a simple and effective molecular design strategy to optimize the active layer morphology of OSCs for improving photovoltaic performance.

Automated summary

In this study, a ternary copolymerization approach was used to develop a new terpolymer donor PM6-Tz20 with improved active layer morphology, leading to enhanced PCE in OSCs. By replacing Al with Ag as the cathode, the champion PCE was further improved, demonstrating the effectiveness of molecular design strategy in optimizing OSC performance.