Optimizing Phase Separation and Vertical Distribution via Molecular Design and Ternary Strategy for Organic Solar Cells with 19.5% Efficiency

Achieving finely tuned phase separation and vertical distribution within the photoactive layer is crucial for enhancing charge transport, thereby significantly influencing the photovoltaic performance of organic solar cells (OSCs). In this study, a nonfullerene acceptor, denoted as HLG, is designed and synthesized by introducing hydrophobic 1,2,4,5-tetrafluoro-3-((2-ethylhexyl)oxy)benzene as the side chains. The fluorine-substituted functional groups endow HLG with higher surface energy, thereby rendering it suitable for utilization as a morphological regulator in the PB2:BTP-eC9 blends. The morphology study reveals that HLG plays an important role in the formation of a favorable phase separation and vertical phase distribution. Benefiting from the desirable morphology, the PB2:HLG:BTP-eC9-based OSC demonstrates an impressive power conversion efficiency (PCE) of 19.5%. This study introduces an effective approach that combines molecular design and the ternary strategy to optimize phase separation and vertical distribution within the active layer simultaneously, leading to significant improvements in the PCE of the OSCs.