Spent coffee ground-derived CQDs for enhanced bifacial DSSC Photoanodes: a stokes shift approach to boost current density and charge transfer efficiency

Abstract This study explores spent coffee ground–derived carbon quantum dots (CQDs) as Stokes-shift additives for bifacial dye-sensitized solar cells (DSSCs). Microwave-synthesized CQDs exhibit red emission at ~630 nm under 400 nm excitation, enabling spectral down-conversion and Förster energy transfer that complement N719 dye absorption. CQDs (2.5 –10.0 mg mL⁻¹) were incorporated into ~8 µm TiCl₄-treated translucent TiO₂ photoanodes. The optimal device (5.0 mg mL⁻¹) delivered a cumulative bifacial efficiency of 5.13%, with charge-collection efficiencies of 68.26% (front) and 66.92% (back), and photocurrent densities of 14.70 and 1.66 mA cm⁻², respectively, demonstrating enhanced spectral utilization and charge transport.