Characterization of CBD-CdSe_1-yS_y deposited at low-temperature for photovoltaic applications

We present the structural and optical characterization of cadmium selenide sulphur (CdSe_1-yS_y) deposited by chemical bath deposition (CBD) technique at low-temperature (20 ± 2 °C). The sulphur molar fraction is varied from 0 to 42.13%. The chemical stoichiometry is estimated by energy-dispersive X-ray spectroscopy (EDS). The CdSe_1-yS_y shows hexagonal wurtzite crystalline phase, which was found by X-ray diffraction (XRD) analysis and it was confirmed by Raman spectroscopy. The average grain size of the CdSe_1-yS_y films was ranged from 1.20 to 1.68 nm that was determined by Debye-Scherrer equation from W(002) direction and it was confirmed by high resolution transmission electron microscopy (HRTEM). This average grain size indicates a high quantum confinement because of it is smaller than the Bohr radii of CdS (2.8 nm) and CdSe (4.9 nm). Raman spectra show two dominant vibrational bands about 208 and 415 cm^-1 associated at CdSe-1LO-like and CdSe-2LO-like. By transmittance measurements at room temperature are found that the optical band gap energies vary from 1.86 to 2.16 eV in the range of investigated sulphur molar fraction. Room temperature photoluminescence shows radiative bands in the visible range and a dominant band in the UV range, approximately 3.0 eV, which can be associated with a radiative transition, bound exciton to donor impurity.