Green allium fistulosum derived nitrogen self-doped carbon dots for quantum dot-sensitized solar cells

Considering the environment protection and low production cost, allium fistulosum was employed to synthesize nitrogen self-doped carbon quantum dots (CQDs) via the one-pot hydrothermal method as sensitizer in QDSCs for the first time. The morphological and structural characteristics, optical performance and energy level structure of CQDs were systematically investigated. The blue-fluorescence CQDs with an average size of 11.67 nm were filled with enormous functional groups, such as hydroxyl, carbonyl and amidogen, which endowed the as-prepared CQDs with hydrophily and stability in aqueous system. The HOMO and LUMO levels of the CQDs were -5.22 eV and -3.80 eV respectively, which matched well with the energy levels of TiO2 and the electrolyte. All the above showed that the CQDs were suitable as sensitizers for quantum dot-sensitized solar cells (QDSCs). Therefore CQD-based QDSCs were experimentally fabricated, yielding the best power conversion efficiency (PCE) of 0.45% with a good fill factor of 0.60. The influence of sensitized time on PCE of QDSCs was studied, and 24 h was selected as the best condition in this work. Finally, the influence factors of CQDs on the photoelectric properties of QDSCs have been discussed, indicating the future research directions of optimized QDSCs.