Indeno[1,2-b]indole-based organic dyes with different acceptor groups for dye-sensitized solar cells

Four new metal-free organic dyes QX15 – 18 based on indeno[1,2- b ]indole have been successfully designed and synthesized. These D–π–A type dyes consist of an indeno[1,2- b ]indole donor and a benzene or thiophene π-bridge. In an attempt to tune their photoelectric properties, the effects of different acceptor groups including cyanoacrylic acid, rhodanine-3-acetic acid, and 2-(1,1-dicyanomethylene)rhodanine (DCRD) have been investigated. The dye QX15 with a cyanoacrylic acid acceptor exhibited a highest V oc of 813 mV and a high J sc of 11.0 mA cm −2 , generating a highest power conversion efficiency of 6.29%. Meanwhile, the dye QX18 with a DCRD acceptor and a thiophene π-bridge showed a significantly improved J sc of 11.9 mA cm −2 , which could be attributed to its red-shifted absorption spectra and high molar absorption coefficient.