Synthesis and Photophysical Properties of Bromination the Small-Molecule Acceptor for Organic Solar Cells

At present, the modification of the benzene ring based terminal group IC is widely studied and a series of progress has been made. Our work designed and synthesized a new brominated fused ring small molecule receptor FBDTEH-2Br by introducing bromine atoms into terminal group. On the one hand, the electron-withdrawing effect of bromine enhances the push-pull electron effect between the core electron-donating segment and the end-capping group, making the absorption spectrum of FBDTEH-2Br more suitable. It shows broad absorption in the range of 600-800 nm in solution, the maximum absorption peak of FBDTEH-2Br in solution is 742nm, While for the thin film, the absorption extended broader with an obvious red-shift in the range of 800-900 nm, it is beneficial to higher J_SC. The maximum absorption peak is 800nm in the film, which can be explained by it's nearly planar structure and the good intermolecular π-π stacking in the solid state caused by the dibromide IC. On the other hand, the introduction of Br atoms will also enhance the intermolecular interactions and improve the electron mobility. The optical band gap of FBDTEH-2Br is 1.43 eV. These results demonstrated that due to the bromine atom has a larger size, the end groups of adjacent molecules still exhibit strong interactions with short π-π distance Because of the O•••S and Br•••S interactions, which is beneficial for the charge to transport along multidirections. Therefore, the introduction of bromine atoms into theterminal group to design and synthesize new brominated small molecule acceptors is expected to obtain better performance in organic solar cell materials.