Morphology Regulation Is Achieved by Volatile Solid Additives in Halogen-Free Solvents to Fabricate Efficient Polymer Solar Cells

The meticulous control of micromorphology in high power conversion efficiency (PCE) of polymer solar cells (PSCs) typically relies on halogenated solvents, which pose serious threats to both environmental sustainability and human health. In this work, a green and efficient method for fabricating high PCE PSCs with halogen-free solvents is developed. By introducing volatile solid additives 1-bromo-2,6-dichlorobenzene (DIB) and 1-bromo-2,3,5-trichlorobenzene (TIB) into toluene solvents, the aggregation behaviors of PM6:L8-BO were meticulously regulated, forming distinct fibrous morphology; in detail, the micromorphology of vertical direction exhibited a distinct pattern of acceptor enrichment at the top and donor enrichment at the bottom, which leads to enhanced exciton dissociation efficiency, improved charge transport performance, significantly reducing charge recombination, and finally improved PCEs, as the maximum PCEs were 18.56 and 17.67%, respectively, which are notably higher than those of devices without additives. Furthermore, since the solid additives can be completely removed from the active layer, the additive-treated devices exhibit superior morphology and photovoltaic stability. This work, therefore, unveils a straightforward and environmentally friendly method for preparing efficient PSCs, which is instrumental in facilitating the large-scale commercialization of PSC technology.