Improving the efficiency and stability of binary small-molecule organic solar cells by incorporating a small amount of polymer acceptor

Small-molecule organic solar cells (SMOSCs) have the advantage of good reproducibility with the low batch-to-batch variation of small-molecule materials, but they may have poor stability due to the unstable morphology of the all-small-molecule-based active layers. Introducing polymer acceptors into binary SMOSCs to construct novel ternary devices can be a good approach to alleviate the dilemma. Herein, a narrow bandgap small-molecule acceptor (S-A), M36, is blended with a medium bandgap small-molecule donor (S-D), BTR-F, to fabricate all small-molecule binary devices. After delicate optimization, the resulting best-performing SMOSC shows a high power conversion efficiency (PCE) of 10.14%. When a polymer acceptor (P-A), N2200, is adopted as a third component (10 wt%) into the host blend system BTR-F : M36, S-D/S-A/P-A-type ternary OSCs with enhanced performance are achieved. Incorporation of the small amount of polymer acceptor into the binary system can effectively improve the morphology of the resulting active layer thereby leading to an excellent PCE of 12.19% for the ternary device based on BTR-F : M36 : N2200. More importantly, improved stability can be achieved for the ternary device compared with that for the BTR-F : M36-based binary device. These results indicate that the strategy of adding a small amount of polymer acceptor into binary small-molecule systems is promising to improve both the efficiency and stability of SMOSCs.