Highly Efficient Acceptors with a Nonaromatic Thianthrene Central Core for Organic Photovoltaics

Despite the great role in determining molecular packings and organic photovoltaic outcomes, very rare candidates could be employed as central cores in current high-performance acceptors except diimide-based moieties. Herein, a new type of central core of nonaromatic thianthrene is explored firstly, affording an exotic but structurally tailorable molecular platform for acceptor design. A unique puckered rather than planar conformation of central core is adopted, caused by the 4n πe^- feature, great ring strain and largely the insufficient p-π orbital overlap of lone pair on sulfur of thianthrene and coterminous benzene planes. As a result, the absorption of thianthrene-based acceptors (CS1, CS2, and CS3) shows unexpected blue shift comparing to the phenazine-based counterpart (CH20), regardless of the intrinsically strong electron-donating characteristic of low valence sulfur atoms. Even so, the desired molecular packing and fibrillary film morphology, assisted by the suitable chlorination on thianthrene, still contribute to the best device efficiency of 19.0% based on D18:CS2 blends. Such novel work renders an underdeveloped NFA platform with the potentials for achieving PCE of over 20%.