High-Efficiency Thick-Film Organic Cells for Indoor Photovoltaics Printed in Air from Non-Halogenated Solvents

Thick-film organic photovoltaics (OPVs) are key for scalable manufacturing, but increasing active-layer thickness usually lowers power conversion efficiency (PCE) due to charge recombination and limited carrier extraction. We report high-efficiency thick-film OPVs fully processed in air by doctor blading using non-halogenated solvents (o-xylene with 3.5% tetralin) for two non-fullerene acceptor systems: PM6:ITIC-4F and PTQ-10:ITIC-4F. Active layers (100–500 nm) were fabricated by adjusting the coating speed while keeping the ink concentration and gap constant. Under mild drying (40 °C, 2 min), both systems exhibited significant efficiency losses at 1 sun (AM1.5G) as the thickness increased, whereas performance was largely preserved under indoor LED illumination (200 lx and 1000 lx), enabling high performance for thick films. Short thermal post-annealing (80–140 °C, 2 min) further improved PCE by reducing bimolecular recombination and enhancing nanostructure. Optimized PM6:ITIC-4F devices reached 10.2% (300 nm) under 1 sun and 14.78% at 200 lx; PTQ-10:ITIC-4F achieved 11.3% (500 nm) under 1 sun and up to 15.71% at 200 lx. Morphological and structural analysis indicates that the superior thick-film performance of PTQ-10:ITIC-4F is linked to favorable phase behavior, polymer-rich surface composition, and preferential face-on molecular orientation, promoting charge collection. These results demonstrate that low-cost PTQ-10 and non-halogenated air processing can enable industrially relevant, high-performance thick-film OPVs.