Efficient ternary polymer solar cell using wide bandgap conjugated polymer donor with two non-fullerene small molecule acceptors enabled power conversion efficiency of 16% with low energy loss of 0.47 eV

The ternary polymer solar cells (PSCs) were fabricated using a wide bandgap conjugated polymer P and two non-fullerene small molecule acceptors, i.e. Y6 and BThIND-Cl, in which the BThIND-Cl was introduced as the third component. The open-circuit voltage (V-oc) of ternary PSCs increased with the increase of BThIND-Cl content in the acceptors, signifying the formation of an alloy between BThIND-Cl and Y6. We have observed that the energy loss of the ternary PSCs is decreased as compared to the binary counterparts, contributing to the improvement in V-oc of ternary PSCs. The short circuit current as well as fill factor (FF) of the ternary PSCs were also enhanced with 0.4 weight ratio of BThIND-Cl in the acceptors i.e.P:BThIND-Cl:Y6 (1:0.4:1.1), resulting in overall power conversion efficiency (PCE) up to 16.08% of the optimized ternary PSCs. The improvement in the short circuit current and FF of the ternary PSCs is originated from the more molecular packing and molecular crystallinity, efficient light harvesting, excess exciton generation dissociation, and balanced charge transport. Moreover, the low value of the energy loss (0.47 eV) which may be lowest for the ternary based PSCs with PCE exceeding 16% which may be originated from the suppressed non-radiative recombination loss. The might be due to the small highest occupied molecular orbital offsets between the combined alloyed acceptor and donor, resulting to the improvement in V-oc for ternary PSC as compared to P:Y6 based PSCs.