Solvent-Induced Polymorphism Influences Efficiency in Organic Solar Cells

Understanding and mitigating performance variability are important for developing organic photovoltaics (OPVs), which are often governed by solid-state organization of molecular entities in semiconductor thin films. This is why achieving structural resolution is essential. This study demonstrates how often-hidden structural polymorphism profoundly influences the power conversion efficiency (PCE) of bulk heterojunction (BHJ) OPVs. The devices consisting of PM6:Y6 BHJ layers cast from low-boiling chloroform (CF; PCE ≈ 15%) and high-boiling o-xylene solvents (o-XY; PCE ≈ 10%) exhibit morphology-dependent optical absorption, charge transport, and recombination dynamics. A synergistic multimodal characterization combined with device physics reveals that the retention of solvents and additives leads to polymorphous BHJ layers, contributing to performance variation. These results strengthen the conclusion that green solvent selection should be guided not only by environmental considerations but also by a thorough understanding of structure–property interrelations, which are vital for improving material performance in OPVs.