Benzotriazole-based 3D 4-Arm Small Molecules Enable 19.1% Efficiency for PM6:Y6-based Ternary Organic Solar Cells.

Abstract

The third component featuring a planar backbone structure similar to the binary host molecule has been the empirical formula for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3-dimensional structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal-modified (rhodanine, thiazolidinedione, and dicyano-substituted rhodanine) benzotriazole (BTA) units, affording three 4-arm molecules, SF-BTA1, SF-BTA2, and SF-BTA3, respectively. After adding these three materials into the classical system PM6: Y6, the resulting ternary devices obtained ultra-high power conversion efficiencies (PCEs) of 19.1%, 18.7%, and 18.8%, respectively, compared with the binary OSCs (PCE = 17.4%). SF-BTA1-3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF-BTA1-3 also acts to enhance charge generation. Introducing SF-BTA1-3 could form acceptor alloys to modify the molecular energy level and inhibit the self-aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi-arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi-arm materials could make OSCs more stable and efficient.