Dramatically boosted efficiency of small molecule solar cells by synergistically optimizing molecular aggregation and crystallinity

For the given organic donor and acceptor materials, optimizing molecular aggregation and crystallinity for appropriate phase separation plays a crucial role in achieving high performance solar cells. In this study, the power conversion efficiency (PCE) of DR3TSBDT:PC71BM based small molecule solar cells (SMSCs) was markedly raised from 7.25% to 9.48% for active layers processed with 0.2 vol % 1,8-diiodooctane (DIO), resulting from the improved fill factor (FF) and short circuit current density (JSC). The performance improvement may be attributed to an appropriate DR3TSBDT molecular aggregation and crystallinity, as well as the optimized phase separation. The influence of DIO concentrations on DR3TSBDT molecular aggregation can be confirmed from the red-shifted absorption and photoluminescence peaks of films along with increase of DIO concentrations. Meanwhile, the ratio of hole/electron mobility approached 1.06 in the optimized SMSCs well according with the highest FF of the corresponding SMSCs. The morphology characterizations indicate that DR3TSBDT molecular aggregation and crystallinity could be finely adjusted by doping appropriate DIO additive.