Synthesis and characterization of hole transporting materials containing bis(carbazole) groups for solid-state dye-sensitized solar cells

In this study, bis(carbazole) derivatives, such as bis[N-(2-ethylhexyl)-carbazole-3-yl] (HTM_I) and bis[N-(2-ethylhexyloxylphenyl)-carbazole-3-yl] (HTM_II), were successfully synthesized for use as small-molecule organic hole-transporting materials (HTMs) in solid-state dye-sensitized solar cells (ssDSSCs) by coupling two respective carbazole moieties using FeCl3 catalyst. The structural integrity of two compounds was identified by 1H and 13 NMR. Maximum UV-vis absorption and photoluminescence peaks were observed at 306 nm and 425 nm for HTM_I, and at 306 nm and 425 nm for HTM_II, respectively. From the optical and electrochemical characterization, bandgap, HOMO, and LUMO energy levels were measured to be 3.26 eV, −5.52 eV, and −2.26 eV for HTM_I, and 3.37 eV, −5.61 eV, and −2.24 eV for HTM_II. The ssDSSC fabricated with HTM_II doped with TBP, MPII, and LiTFSI showed the highest PEC of 2.54%, with Jsc = 6.55 mA/cm2, Voc = 0.55 V, and FF = 0.70.