Enhancing the Stability of ITO-Free Organic Photovoltaics under Low-Light Irradiation via Ternary Blend Strategy

The commercialization of ITO-free organic photovoltaics (OPVs) for low-light applications (e.g., IoT systems) is limited by low-efficiency operational stability, primarily due to morphological degradation in bulk-heterojunction (BHJ) active layers. Here, we demonstrate that incorporating phenyl-C61-butyric acid methyl ester (PC61BM) as a ternary component in PM6:ITIC-based OPV significantly extends the device lifetime under 1000 lx LED irradiation. Using a Ti/Al/Ti cathode and MoO3/Ag anode, the optimized ternary blend PM6:ITIC:PC61BM (10:6:4 weight ratio) based OPV device achieves a T80 of 3300 h. Atomic force microscopy and photoluminescence investigations indicate that the introduction of PC61BM suppresses the phase separation between the donor and acceptor and preserves the electroluminescence quantum efficiency (EQEEL), mitigating nonradiative voltage losses (ΔVnr). The ternary system also enhances power conversion efficiency (PCE) under 40,000 lx LED illumination from 12.03% to 13.88% due to the more efficient exciton dissociation. This work addresses the critical gap in understanding the degradation mechanisms of ITO-free OPVs under low-light stress.