As low-cost high-efficiency photovoltaic devices, dye-sensitized solar cells have received wide attention since being reported. Five novel D-A-pi-A metal-free organic dyes derived from IQ1 were studied by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The band gaps of the designed dyes are significantly decreased, and the intramolecular charge transfer capabilities are still analogous to IQ1. In addition, their absorption spectra show more pronounced red shifts with sufficient oscillator strengths than the reference dye. The LHE curves exhibit that they have efficient light harvesting efficiency and are closer to the solar spectrum. The significant increase in short-circuit current density contributes twice the overall estimated efficiency compared to the reference dye IQ1. In particular, the four designed dyes IIQ, IOQ, ITQ and ISQ, as the most promising candidates, have overall power conversion efficiency over 15% with short-circuits current density over 26.62 mA.cm(-2) and open-circuit voltage over 794.61 mV, up 95.7% and 15.9% than IQ1, respectively. Our work is expected to provide guidance for the development of new high-efficiency dye-sensitized solar cells.