Photostable Squaraine Dimers For Organic Solar Cells With A High Open Circuit Voltage Exceeding 1.0 V

Squaraines (SQs) have been demonstrated as one of potential low-cost donor materials for organic solar cells (OSCs), for which the performances however are limited by low open circuit voltage (V-OC). Herein, we show a new molecular design strategy that can achieve SQ-based OSCs with high V(oc)s exceeding 1.0 V by constructing butterfly-shaped SQ dimers. Through using branched-alkyl substituted carbazole as the bridge unit and fluorinated indole derivatives as the end-groups, the resulting dimers DSQ4-5 show deep-lying HOMO levels, enhanced photostability, high hole mobility and good compatibility with fullerene acceptors. Impressively, the resulting device V(OC)s for both dimers can reach 1.0 V through blending with PC71BM acceptor, together with rather low energy losses (E(loss)s) of similar to 0.6 eV, outperforming most of SQ-based donors reported so far. In addition, we found that the processing solvents have a pronounced effect on the blend film morphology and the device performance, while DSQ4-based devices processed by chlorobenzene can deliver the best efficiency of similar to 3%.