Novel Red Light-Absorbing Organic Dyes Based on Indolo[3,2-b]carbazole As the Donor Applied in Co-Sensitizer-Free Dye-Sensitized Solar Cells

Three novel organic dyes (, and ), based on indolo[3,2-b]carbazole as the donor and different types of electron-withdrawing groups as the acceptors, were synthesized and successfully applied in dye-sensitized solar cells (DSSCs). Their molecular structures were fully characterized by H NMR, C NMR and mass spectroscopy. The density functional theory (DFT) calculations, electrochemical impedance spectroscopy analysis, UV-Vis absorption characterization and tests of the solar cells were used to investigate the photophysical/electrochemical properties as well as DSSCs' performances based on the dyes. Dye showed the broadest light-response range (300-770 nm) in the incident monochromatic photo-to-electron conversion efficiency (IPCE) curve, due to its narrow bandgap (1.95 eV). However, dye exhibited the best device performance among the three dyes, with power conversion efficiency of 5.41%, J of 12.55 mA cm, V of 745 mV and fill factor (FF) of 0.59. We also found that dye aggregation was efficiently suppressed by the introduction of alkylated indolo[3,2-b]carbazole, and, hence, better power conversion efficiencies were observed for all the three dyes, compared to the devices of co-sensitization with chenodeoxycholic acid (CDCA). It was unnecessary to add adsorbents to suppress the dye aggregation.