To make quantum dot sensitized solar cells (QDSCs) competitive, a power conversion efficiency (PCE) comparable to other developing solar cells is required. Significant attention has been paid to undoped or nitrogen (N) doped carbon quantum dots (N-CQDs) for use as sensitizers or light harvesters in solar cells. However, to our knowledge, the nitrogen and sulfur (S) co-doped CQDs (N, S-CQDs) have never been used as the absorbing layer alone. In the present work, we synthesize nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) from a single precursor thioacetamide (TA), via a hydrothermal method. The as-prepared N, S-CQDs were employed as a ‘‘green” photoactive layer in TiO2 film, as photoanode. The solar cell delivered an open-circuit voltage (Voc) of 0.43 V, short-circuit current (Jsc) of 0.61 mA/cm-2, fill factor (FF) of 52 %, and PCE of 1.36%; highest among all the carbon-based QDSCs. Moreover, Device-NS showed more stability over 48 h compared to Device-C and Device-N. Undeniably, the achieved PCE is not satisfactory; however, the upgraded device fabrication and structural design may improve PCE and current densities while sustaining the high open-circuit voltage. This study demonstrated the potential application of N, S-CQDs for low-cost, ‘‘green” quantum dot solar cell applications.