A polymer donor with versatility for fabricating high-performance ternary organic photovoltaics

The success of ternary organic photovoltaics (OPVs) has led to more attention being placed on understanding the mechanism through which the third component can affect the performance. In this study we embedded the conjugated polymer PTO2 as the third component in PM6:Y6 and PM6:BTP-eC9 blends and investigated the optoelectronic properties of the resulting efficient and stable OPVs. PTO2 displayed complementary absorption, high miscibility, and a HOMO energy level deeper than that of PM6, thereby enhancing the degrees of light harvesting, forming suitable blend morphologies, and lowering the energy losses of the devices, respectively. The miscibility of PTO2 with the acceptor altered the molecular packing of the ternary blend films and resulted in the optimized PM6:Y6 and PM6:BTP-eC9 OPVs having power conversion efficiencies of up to 17.05 and 18.01%, respectively. Furthermore, the embedding of PTO2 improved the long-term stability of the devices when exposed to light (halogen lamp; 0.67 mW/cm², 740 lx), heat (85 °C, argon), or water/oxygen (without encapsulation; air of 40% humidity). Our results provide guidelines for the design of stable high-performance ternary OPVs.