18.02% Efficiency ternary organic solar cells with a small-molecular donor third component

Ternary strategy is one of the most effective approaches to boost the power conversion efficiency (PCE) of organic solar cells (OSCs) and overcome the trade-off between photovoltage and photocurrent that sets limitation on the performance enhancement of regular binary devices. Herein, a small-molecule (SM) donor BPR-SCl, with deep-lying highest occupied molecular orbital (HOMO) energy level and strong crystallinity, was elaborately selected as the third component in the PM6:BTP-eC9 host binary blend to fabricate ternary organic solar cells (TOSCs). The doping of BPR-SCl is found to enhance the crystallinity of the photoactive layers but slightly reduce the donor/acceptor phase separation scale. The TOSCs with 20 wt% BPR-SCl in donors delivered a high PCE of 18.02% together with the enhanced V-oc and J(sc), which was ascribed to the deep-lying HOMO energy level, broadened absorption spectra, improved exciton separation process and faster hole transfer. To the best of our knowledge, this is the highest PCE for TOSCs using SM donor as the third component reported so far, which provides new insight in achieving high-performance TOSCs.