Nanocomposite Photoanodes Consisting of p-NiO/n-ZnO Heterojunction and Carbon Quantum Dot Additive for Dye-Sensitized Solar Cells

To increase the performance of power conversion efficiency of dye-sensitized solar cells (DSSCs), in the current paper, nanocomposites of n-type ZnO and p-type NiO semiconductors were constructed as photoanodes in DSSCs. Furthermore, the influence of the addition of carbon quantum dots on the nanocomposites of n-ZnO and p-NiO was evaluated. The efficiency achieved was 1.58 times of that of ZnO with addition of 8 wt % NiO. Moreover, the doping of carbon quantum dots in the nanocomposites of ZnO/NiO(8 wt %) enhanced the efficiency up to 3.8 times of that of ZnO/NiO(8 wt %). The value (13.02% (430 nm LED@100 W/m2)) was the highest among that of the carbon dot-incorporating DSSCs. NiO and ZnO semiconductors created a p–n heterojunction, gave rise to faster separation of charges, and minimized the recombination of electrons. Carbon quantum dots promoted the charge carrier transport by converting photon to charge and reducing the potential barrier of the charge carrier at the interfaces of n-ZnO/carbon dots and carbon dots/p-NiO. These results suggest that the adequate selection of the band gap energy levels of the materials induces the preferable charge separation. Especially, the effect reducing the potential barrier of charge carriers by carbon quantum dots is prominent to improve the photovoltaic efficiency of the DSSCs. Thus, the nanoscale materials of ZnO, NiO and Cdots were promising for the enhancement of photovoltaic performance.