Enhancement of photoelectric conversion efficiency with sulfur-doped g-C₃N₄/TiO₂ nanoparticles composites in dye-sensitized solar cells

S-doped g-C₃N₄/TiO₂ nanoparticle composites (TCNS) were generated by successfully calcinating a compound of thiourea and TiO₂ at 550 °C; these composites serve as a promising photoanode material for dye-sensitized solar cells (DSSCs) with improved efficiency. TEM, HRTEM, XRD, UV–Vis and FTIR results showed that the surfaces of TiO₂ nanoparticles were coated with a thin layer of sulfur-doped g-C₃N₄. The corresponding photoelectrochemical properties of the fabricated DSSCs were also studied. The DSSCs based on the TCNS photoelectrode shows a ratio of 4.87% in converting light into electricity, a short-circuit photocurrent of 10.41 mA cm⁻², and an open-circuit voltage of 0.65 V, qualities which were well above those of DSSCs based on un-doped TCNS. The significant enhancement in DSSC performance is mainly due to the suppression of the recombination of electron–hole (e⁻–h⁺) pairs, suppression which also leads to an increase in open-circuit photovoltage, as well as photocurrent density under short circuit by the layer of sulfur-doped g-C₃N₄. Additionally, electrochemical impedance spectroscopy analysis proved that the electron transfer resistance is considerably reduced, and this reduction increases the power conversion efficiency.