Soft Polymeric Matrix-Mediated Stabilization of Bulk Heterojunction Morphology for Thermally Robust Organic Photovoltaics.

Suppressing thermally driven morphological evolution while preserving efficient charge transport pathways remains a critical challenge for improving the long-term stability of organic photovoltaics (OPVs). Herein, a soft polymeric matrix strategy based on gel-related soft material concepts is demonstrated for stabilizing bulk heterojunction (BHJ) morphology and simultaneously improving the efficiency and thermal durability of OPVs. The incorporation of an optimal 5 wt% polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) as a soft polymeric matrix component into a PM6:Y6 blend modulates the nanoscale morphology and local packing characteristics of the acceptor phase. These changes improve charge-transport balance and charge collection, increasing the power conversion efficiency (PCE) from 14.27% to 15.22%, corresponding to a 6.7% relative enhancement over the control device. More importantly, after 10 days of thermal aging at 85 °C, the SEBS device retains 87.1% of its initial PCE, compared with 72.5% for the control device. Complementary morphological and spectroscopic analyses reveal suppressed thermally induced structural evolution and aggregation in the SEBS-containing films. These findings demonstrate that a gel-related soft polymeric matrix can regulate BHJ organization and mitigate thermally driven morphological evolution, providing a simple strategy for addressing the efficiency-stability trade-off and realizing thermally robust OPVs.