Mitigating the Energy Loss in Ternary Organic Photovoltaics with a Conjugated Terpolymer

We investigated the performance of a terpolymer, PM1, as a third component in two donor–one acceptor-based ternary organic photovoltaics (OPVs). PM1, a derivative of PM6, incorporates 20% thiophene-thiazolothiazole (TTz) monomers, expanding its structural diversity and featuring a lower highest occupied molecular orbital (HOMO) energy level compared to that of PM6. To investigate the impact of PM1, we fabricated p–i–n-structured OPVs with the following layer configuration: ITO/PEDOT:PSS/PM6:Y6 (or BTP-eC9) with or without PM1/PFN-Br/Ag. By examining the component miscibility and blend film morphology, we explored how these factors influence carrier dynamics and ultimately impact the OPV performance. The high compatibility between PM1 and PM6 (χ_PM6-PM1 = 0.003) facilitated the formation of a well-mixed donor phase, akin to an alloy. This homogeneous blend promoted efficient charge transport and suppressed trap-assisted recombination within the blend film. Consequently, PM1-based ternary OPVs exhibited reduced nonradiative recombination, leading to an increased open-circuit voltage (V_OC) and overall device efficiency. The optimal power conversion efficiencies of the ternary OPVs using Y6 and BTP-eC9 as acceptors reached 17.09 and 17.60%, respectively. Our findings highlight the potential of terpolymers as promising materials for efficient ternary OPVs, paving the way for innovative donor polymer design strategies.