Nonfullerene Acceptor Featuring Unique Self-Regulation Effect for Organic Solar Cells with 19 % Efficiency

The blend nanomorphology of electron-donor (D) and -acceptor (A) materials is of vital importance to achieving highly efficient organic solar cells. Exogenous additives especially aromatic additives are always needed to further optimize the nanomorphology of blend films, which is hardly compatible with industrial manufacture. Herein, we proposed a unique approach to meticulously modulate the aggregation behavior of NFAs in both crystal and thin film nanomorphology via self-regulation effect. Nonfullerene acceptor Z9 was designed and synthesized by tethering phenyl groups on the inner side chains of the Y6 backbone. Compared with Y6, the tethered phenyl groups participated in the molecular aggregation via the pi-pi stacking of phenyl-phenyl and phenyl-2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC-2F) groups, which induced 3D charge transport with phenyl-mediated super-exchange electron coupling. Moreover, ordered molecular packing with suitable phase separation was observed in Z9-based blend films. High power conversion efficiencies (PCEs) of 19.0 % (certified PCE of 18.6 %) for Z9-based devices were achieved without additives, indicating the great potential of the self-regulation strategy in NFA design. The self-regulation effect is well demonstrated by finely tuning the aggregation behavior of nonfullerene acceptor (NFA) Z9, where the tethered phenyl groups worked as endogenous additives and participated in intermolecular packing enabling the formation of 3D charge transport channels with super-exchange electron coupling. NFA Z9 forms optimal nanomorphology with polymer donors without external additives, and a high PCE of 19.0 % is achieved.+image

Automated summary

By utilizing self-regulation effect, we have successfully controlled the aggregation behavior of nonfullerene acceptor Z9 in both crystal and thin film nanomorphology, achieving optimal nanomorphology with polymer donors and high power conversion efficiency.