A new dithienylthienothiadiazole-based organic dye (D) was synthesized by a seven-step synthetic route for use as a sensitizer in dye sensitized solar cells (DSSCs). The dye contains a dithienylthienothiadiazole central unit and two cyanoacrylic acid anchoring side groups. Optical and electrochemical properties of D were evaluated. In addition, density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were carried out. A favorable electronic excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) indicated that the dye can be used as a sensitizer for DSSC applications. The photovoltaic properties of laboratory scale optimized DSSCs sensitized with D showed a power conversion efficiency (PCE) of 4.22%, which was further improved to 5.47% upon the addition of chenodeoxylic acid (CDCA) as a coadsorbant.