Expanding the Processing Window of D18 Donor Polymers through Thiophene Incorporation for Large-Area Organic Photovoltaics

Developing donor polymers compatible with scalable and eco-friendly manufacturing remains a critical challenge for the lab-to-fab transition of organic photovoltaics (OPVs). Here, we report a series of D18-based terpolymers incorporating controlled amounts of thiophene or hexylthiophene comonomers to systematically expand the processing window while preserving the optoelectronic characteristics of the parent polymer. Compared to pristine D18, thiophene-engineered terpolymers (P5T and P15T) exhibit enhanced solubility, improved film uniformity, and superior device reproducibility under ambient blade-coating conditions. Notably, P15T uniquely enables the fabrication of uniform active layers from o-xylene, a green solvent generally incompatible with D18-based systems. Although the resulting devices exhibit a moderate decrease in PCE relative to chloroform-processed counterparts, this capability substantially broadens the processing window and represents an important step toward more sustainable organic photovoltaic manufacturing. Devices fabricated under an ambient atmosphere with a large active areas (0.55 cm2) achieve power conversion efficiencies up to 8.66%, demonstrating competitive performance under industrially relevant constraints. In contrast, hexylthiophene-rich analogues show reduced molecular weight, poor film formation, and limited photovoltaic performance, highlighting the narrow design window between solubility enhancement and electronic disruption. Overall, this work demonstrates that subtle backbone engineering enables decoupling of solubility and electronic properties in high-performance donor polymers. These findings establish practical molecular design guidelines for scalable, green-solvent-processed OPVs and contribute to bridging the gap between laboratory-scale efficiency and industrial manufacturing.