Design and fabrication of hybrid carbon dots/titanium dioxide (CDs/TiO₂) photoelectrodes for highly efficient dye-sensitized solar cells

Hybrid carbon dots/titanium dioxide (CDs/TiO₂) photoelectrodes for use in high-performance dye-sensitized photovoltaic solar cells were obtained by a facile one-step hydrothermal approach. The structural, morphological, and optical properties of the as-obtained samples were analyzed by powder X-ray diffraction analysis, transmission electron microscopy, Raman spectroscopy, ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy, and photoluminescence spectroscopy, revealing anatase crystal structure with individual spherical molded nanoparticles for both TiO₂ and the composite samples. The size of the nanoparticles ranged from 30 to 40 nm, being consistently decorated on the carbon dots. The CDs/TiO₂ samples exhibited enhanced surface area (112 m²/g) and pore size (30–35 nm) compared with bare TiO₂ (77 m²/g and 42–48 nm), which is invaluable for improving solar cell efficiency. The J–V characteristic illustrated that the CDs/TiO₂ photoanode resulted in high photovoltaic conversion efficiency (PCE) of 15.5% compared with 7.8% when using bare TiO₂. These results suggest that incorporation of carbon dots enhanced the PCE of the cells using bare TiO₂. A mechanism for this improvement is also proposed in detail.