Thioacetamide-derived nitrogen and sulfur co-doped carbon quantum dots for “green” quantum dot solar cells

Nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) were synthesized from a single precursor thioacetamide (TA), via a hydrothermal method. The method is facile and N, S-CQDs are synthesized with no need for surface ligands, high temperature, or other intricate chemical techniques. The as-prepared N, S-CQDs were employed as a “green” photoactive layer in TiO2 film, as photoanode, using a Pt counter electrode and I- 3/I- electrolyte. The solar cell delivered a PCE of 1.36%; highest among all the carbon-based QDSCs. • The gap between conduction bands of carbon quantum dots (CQDs) and TiO 2 was reduced by heteroatom doping. • Thioacetamide-derived Nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) were prepared. • N, S-CQDs-based device showed superior performance over CQDs or N-CQDs-based devices. • N, S-CQDs-based solar cell device (Device-NS) delivered 1.36% power conversion efficiency; highest among all the carbon-based QDSCs. 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 TiO 2 film, as photoanode. The solar cell delivered an open-circuit voltage (V oc ) of 0.43 V, short-circuit current (J sc ) 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.