The effects of Se/S ratio on the photoelectric properties of nitrogen -doped graphene quantum dots decorated CdSxSe1-x composites

In the work, CdS_xSe_1-x/N-GQDs composites were fabricated via a simple one-step hydrothermal process and their tunable composition, structure and photoelectric properties were characterized by various techniques. The photoelectric properties of CdS_xSe_1-x/N-GQDs could be adjusted by different Se/S ratios and tunable band-gaps. CdS_xSe_1-x/N-GQDs composites reached the optimal photocurrent response and the lowest interfacial impedance at the Se/S ratio of 0.75:0.25. Mott-Schottky plots and LSV spectra showed that the n-type CdS_0.25Se_0.75/N-GQDs presented a higher carrier density under light illumination. The excellent properties of the composites could be attributed to the mechanism involved in the excitation and electron-transfer process. On one hand, the band-gap of CdS_0.25Se_0.75/N-GQDs was narrowed, and more electrons were excited by the lower band-gap energy to promote a superior electron separation and transportation. On the other hand, N-GQDs acted as charge carriers and conductive way providers for electron-transfer instead of electron-hole recombination in the composites.