Performance improvement of dye sensitized solar cells based on cadmium sulfide/S, N co doped carbon dots nanocomposites

In this paper, cadmium sulfide (CdS), sulfur and nitrogen co-doped carbon dots (S,N-CDs) and cadmium sulfide/sulfur and nitrogen co-doped carbon dots (CdS/S,N-CDs) were prepared via hydrothermal route. Cadmium acetate dihydrate, thiourea and citric acid were applied as a source of cadmium, sulfur and carbon respectively. Thiourea plays dual role as a dopant source for doping of carbon dots and sulfur source for the synthesis of cadmium sulfide. The influence of hydrothermal temperature on the morphology of CdS and CdS/S,N-CDs was determined in terms of structure, size and morphology through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR) analysis. Results showed that temperature has a significant effect on the morphology of cadmium sulfide. Homogenous flower like morphology of CdS in 160 °C was converted to non-homogenous worm-like particles at 200 °C. Moreover, the flower-like morphology of CdS was converted to the particle morphology during the preparation of CdS/S,N-CDs since the acidity of solution is changed for the presence of citric acid. After morphological and structural engineering, nitrogen and sulfur co-doped carbon dots and CdS/S,N-CDs were applied in dye sensitized solar cells. The JSC of S,N-CDs and CdS/S,N-CDs were measured 14.07 and 18.38 mA/cm2 respectively. Results showed that the VOC equal to 0.61 V for CDs while decreased to 0.59 V in CdS/S,N-CDs case. Although VOC decreased, hole PCE show improvement in CdS/S,N-CDs case, PCE enhanced from 3.44% to 5.7%.