Electrostatic and Geometric Regulation of "Third Terminal" in Non-Fullerene Acceptors for High-Performance Organic Photovoltaics.

Inspired by the dominant role of 2-(3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (INCN) terminal in regulating molecular packing, an innovative strategy to construct "third terminals" of non-fullerene acceptors (NFAs) is proposed by introducing INIC-mimicking motifs to molecular backbone center. Through delicate electrostatic and geometric regulation of INCN analogues (NQ, DCNQ, and TCNC), newly designed NFAs (CH56, CH57, and CH58) render not only an inverted distribution of molecular frontier orbitals, but also the substantial HOMO-LUMO overlap for CH56 while pronounced spatial separation for others. Especially, the puckered TCNC with the most LUMOs distribution yet minimal involvement in molecular packings drives CH58 to adopt a pseudo-three-dimensional (3D) packing network and inferior electron migration in sharp contrast to CH56. Moreover, the twisty CH57 and CH58 also exhibit unexpectedly quenched fluorescence due to the severe skeletal vibrations DCNQ and TCNC, further resulting in the large energy losses and poor photovoltaic performance. Finally, CH56-based OSCs yield a surprising open-circuit-voltage of 1.007 V for binary devices and an excellent 20.16% efficiency for ternary devices. Our trials on "third terminal" has enabled the extensive exploration of novel architectures of NFAs beyond conventional structural paradigms.