Enhanced Performance via End-Group Alteration of Benzodithiophene-Based Donors for Organic Solar Cells: a Theoretical Study.

Donor in organic solar cells (OSCs) is essential for promoting charge transport and enhancing photoelectric conversion efficiency. In this work, five new donors M1-M5 were designed by changing the end group to 3-hexyl-2,4-dithiothiazolidine, dicyano-hexylrhodanine, 1,1-dicyanomethylene-3-indanone, 1,3-indenedione and 1,1-dicyano-5,6-difluoroindanone, respectively.The optoelectronic properties of the six donors and their interfacial properties with the well-known acceptor Y6 were studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT).  The calculation results show that the absorption ranges of M1-M5 in the visible light region are expanded, the red shift degrees of M1 and M3 are obvious (73 nm, 63 nm), and the light absorption abilities are obviously improved. The hole migration efficiency of M2, M4 and M5 is improved, which is beneficial to improve the charge transfer efficiency. The proportion of charge transfer states at the M1/Y6 and M4/Y6 interfaces increased by 7.5% and 2.5%, respectively. Moreover, the charge transfer states generated at the M1/Y6 interface through the intermolecular electric field mechanism and hot exciton mechanism are more dominant. Our calculation results not only provide several potential small molecule donors for experimental synthesis, but also have certain reference value for understanding the charge transfer mechanism at the donor/acceptor (D/A) interface.