Efficient Ternary Polymer Solar Cells Employing Well Matched Medium Band Gap and Narrow Band Gap Nonfullerene Acceptors

We have fabricated a ternary polymer solar cell (PSC) consisting of a P:Y6 host binary bulk heterojunction and medium band gap acceptor 3a with the high lying lowest unoccupied molecular orbital energy level as the second acceptor. The optimized P:3a:Y6 (1:0.2:1.0 wt/wt) showed favorable phase separation morphology, higher and balanced charge mobilities, and energy transfer from 3a to Y6. As a result of these impacts, the ternary PSCs attained an impressive power conversion efficiency (PCE) of 15.96%, which simultaneously increased JSC and VOC and FF, than binary PSCs based on P:Y6 (13.84%) and P:3a (13.41%). The enhancement in the PCE for ternary PSC compared to binary counterpart is attributed to the larger exciton generation, higher energy transfer from 3a to Y6, and significant equalized electron and hole transport owing to the larger phase separation between donor and acceptor domains in the ternary film.