Green synthesis of carbon quantum dots from nutshells for enhanced performance in dye-sensitized solar cells

This study presents a sustainable approach to large scale synthesis of carbon quantum dots (CQDs) from nutshells, a widely available waste from biomass, using hydrogen peroxide (H₂O) as the oxidizing agent in a hydrothermal process. The conditions of synthesis, including concentration of H₂O₂, reaction temperature and time, have been systematically optimized. The results show that optimal conditions include a concentration of 2.5% H₂O₂, a reaction temperature of 180 °C and a reaction time of 12 hours. The obtained CQDs have an average size of 3 nm and excellent fluorescence. The 2 L Parr reactor has been used to increase the production process and make it more viable for industrial applications. By-products of the reaction, including gas, liquid and solid residues, have been analyzed to understand the distribution of carbon. In addition, CQDs have been incorporated in dye-sensitive solar cells (DSSCs) where they have significantly improved the photovoltaic performance, with increased current density and overall efficiency. This work highlights the potential of biomass-based CQDs for the sustainable production of nanomaterials and for energy conversion applications, and offers a scalable and environmentally friendly alternative to synthesis of CQDs.