Multifunctional nitrogen-doped graphene quantum dots incorporated into mesoporous TiO₂ films for quantum dot-sensitized solar cells

Nitrogen-doped graphene quantum dots (N-GQDs) synthesized by a hydrothermal method were incorporated into TiO₂ mesoporous films to boost the photovoltaic performance of quantum dot-sensitized solar cells (QDSSCs). Cadmium selenide quantum dots (CdSe QDs) were then deposited on the N-GQDs-incorporated TiO₂ films using a successive ionic layer adsorption and reaction (SILAR) technique. The N-GQDs serve multiple functions for enhancing light-harvesting, facilitating electron transportation, and suppressing charge recombination. The non-zero gap N-GQDs both generate excitons as co-sensitizer and provide more adsorption sites for CdSe QDs. Furthermore, the N-GQDs provide efficient electron pathways between TiO₂ nanoparticles and passivate the surface defects, giving rise to a high electron diffusion coefficient and long electron lifetime. The resulting QDSSC with the N-GQDs showed significantly improved power conversion efficiency (4.88%) compared to the QDSSC (3.92%) without N-GQDs.