Improving the Photovoltaic Performance of PBDB-T:PC₇₁BM-Based Ternary Solar Cells by Employing Arylmethylene-Substituted Small Molecules as the Guest Acceptor

Four arylmethylene-substituted small-molecule acceptors (SMAs), IDTV-SiIC, IDTVT-PhIC, m-IDTV-PhIC, and DTCFDV-IC were introduced to the host PBDB-T:PC₇₁BM binary system as a guest acceptor to construct PBDB-T:PC₇₁BM:SMA ternary polymer solar cells (PSCs), respectively. After optimization, these ternary PSCs exhibit power conversion efficiencies (PCEs) of 8.93%, 9.28%, 9.68%, and 9.78% for IDTV-SiIC, IDTVT-PhIC, m-IDTV-PhIC, and DTCFDV-IC, respectively, all of which are higher than those of the host binary PSC regardless of the device structures (inverted or conventional devices). The improved PCE is first attributed to the increased open-circuit voltage (V_oc) due to the upshifted lowest unoccupied molecular orbital level of an acceptor alloy between the host acceptor (PC₇₁BM) and the guest acceptors (SMAs). The acceptor alloy model is verified by exploring the relationship between V_oc and the feed ratio of SMA in the acceptor blend, cyclic voltammetry measurements, and miscibility of two kinds of acceptors. Furthermore, the increased fill factors of ternary PSCs also play a key role in improving the PCEs, which could be ascribed to the enhanced and more balanced carrier mobilities, increased exciton dissociation, reduced charge recombination, and the optimized morphology of active layers after such SMAs were added as the guest acceptor. In particular, IDTV-SiIC-based thick-film ternary devices were prepared, and the results demonstrate that the ternary device has a better film thickness tolerance compared with the host binary device, suggesting a great potential of such SMAs in fabricating thick-film photovolatic devices. Additionally, relative to the host PM6:L8-BO binary PSC (17.18%), a higher PCE of 18.20% was achieved in the PM6:L8-BO:DTCFDV-IC ternary PSC, with DTCFDV-IC as the guest acceptor, implying such arylmethylene-substituted SMAs have certain great potentiality in constructing high-efficiency ternary PSCs. This work suggests that the incorporation of these SMAs as the third component to construct ternary PSCs is a feasible and effective strategy to obviously enhance the device efficiency.