Two new indolo[3,2-b]carbazole-based metal-free organic dyes (Dl and D2) were synthesized by utilizing triphenylamine as the first donor which were connected to the second donor indolo[3,2-b]carbazole via 9-position and 8-position, respectively. The dyes were characterized by UV-visible absorption spectra and electrochemical analyses. The both two dyes showed intensive absorption spectra in the wavelength of 300-600 nm and narrow band gap of 2.29 eV for Dl and 2.16 eV for D2. The cyclic voltanunetry indicated that the oxidative potentials and reductive potentials of the dyes were well matched with the energy levels of the I-/I-3(-) redox couple and TiO2 conduction band, respectively. The substituted positions on the indolo[3,2-b]carbazole played important roles in tuning the photoelectronic properties. The dye D2 with 2, 8-substituted indolo[3,2-b]carbazole core shows wider absorption spectrum and lower dye aggregation than D1 with 3,9-substituted isomer. The best power conversion efficiency (PCE) of 6.34% is obtained by the dye D2 due to its wider absorption spectra and strong steric hindrance, which can effectively suppress the undesirable dye aggregation. The co-sensitization of Dl and D2 enhances IPCE response in the visible light region and further improves the PCE up to 7.03%.