Impact of Quinoxaline Units in Random Terpolymers on Enhancing Indoor Organic Photovoltaics: Lowering HOMO Level and Improving Miscibility

The rapid growth in demand for the Internet of Things (IoT) has increased the need for power sources capable of harvesting energy from indoor light sources. Indoor organic photovoltaics (IOPVs) have emerged as promising candidates due to their ability to effectively harness indoor light. However, efficient polymer donors tailored for indoor conditions remain rare, as most high-performance photoactive materials have been developed primarily for outdoor environments. Here, a series of PM6-derived terpolymers, PB2FQxn (n = 5, 10, 15, and 20) is presented, incorporating a quinoxaline-based electron-accepting monomer 2,3-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)-6,7-difluoroquinoxaline (B2FQx) as a third component. Introducing the B2FQx monomeric unit into the polymer backbone enables favorable fine-tuning of the optical, electrochemical, and molecular packing properties. In particular, when blended with L8-BO, PB2FQx15-based devices achieve remarkable power conversion efficiencies exceeding 30% under both light-emitting diode (LED) 1000 lx and fluorescent lamp (FL) 1000 lx illumination. This impressive performance is attributed to the deep-lying highest occupied molecular orbital (HOMO) energy level of PB2FQx15 and its optimal miscibility with L8-BO. Overall, it is demonstrated that the design of terpolymers incorporating the combination of two electron-accepting units paves the way to enhance the photovoltaic properties of IOPVs.