Naphthalene Diimide-Based Small Molecule Acceptors for Fullerene-Free Organic Solar Cells

Abstract

Power conversion efficiency (PCE) of organic solar cells (OSCs) have gradually improved up to 11.83% due to intensive developments of new organic semiconductors, interfacial and morphology engineering. These improvements have mainly resulted from development of novel donor polymers. In bulk heterojunction (BHJ) system, fullerene derivatives including [6,6]-phenyl-C60-butyric acid methyl ester (PC60BM) have been typically used as electron acceptor because of strong electron affinity. However, PC60BM has some disadvantages such as electronic tuning via structural modification and weak absorption in the visible range. Therefore, two novel small molecules based on Naphthalene Diimide (NDI) unit, named as NDI-TR and NDI-TTR, respectively, were designed and synthesized. Compared with NDI-TTR, the optimal PCE of NDI-TR as non-fullerene acceptor blends with PTB7-Th devices reached 3.07%. Especially, the fill factor of the solar cell devices were all above 69%, which is the best result reported for NDI-based small molecule solar cells.