Simple unfused acceptors with optimal naphthalene isomerization enabling 10.72% as-cast organic solar cells

The isomerization strategy is adopted to modulate the molecular packing, optoelectronic and morphological properties of simple unfused acceptors (SUAs) for high-efficiency as-cast organic solar cells (OSCs). We report herein three SUAs (DNO15T, DNO26T and DNO27T) by flanking different naphthalene isomers with thiophene and dithieno[3,2-b:2′,3′-d]pyrrole as the donating cores. The SUAs exhibit narrow optical band gap (ca. 1.62 ∼ 2.04 eV) but largely different absorption profiles. The isomerization exerts great impact in molecular geometry and π-π stacking of SUAs as well as their morphology and photovoltaic properties when blending with polymer donor PBDB-T. The SUA featuring high coplanarity and good compatibility with PBDB-T affords the optimal phase separation morphology, photon harvesting and charge mobility in binary blends. The as-cast binary OSCs deliver a power conversion efficiency of 10.72% and open-circuit voltage of 0.89 V, competing with most reported SUAs based best-performing devices. Our study provides a good guidance for the design of SUAs via optimizing regional isomerization to achieve high-performance as-cast OSCs.