Optical and structure properties of CdTe/CdS films under influence of both CdCl2 heat treatment and (O2+ Ar) atmosphere

Thin flms of CdTe/CdS were prepared using the thermal evaporation technique with pressure 2×10−5 mbar on substrate from
glass. The thickness of CdCl2 layer around 150 nm was deposited making as-deposited CdTe/CdS flms. The flms covered
by cadmium chloride (CdCl2) layer were annealed in atmosphere of (O2+Ar) at diferent temperatures of 400 °C, 450 °C
and 480 °C for 15 min. The efect of CdCl2 as a top layer on morphological, structural and optical properties was studied, and
the results were compared with as-deposited flms and also with (O2+Ar) annealing process. The refractive index in whole
wavelength and flm thickness was estimated by Cauchy dispersion relation and Swanepoel’s envelope method, respectively.
Furthermore, many optical parameters such as transmittance, absorbance, refectance, and optical band gap, Urbach energy,
flm thickness, electronic polarizability, lattice dielectric constant were calculated also in this study. The heat treatment of
our flms with depositing CdCl2 layer in (O2+Ar) fow lowered the energy gap which led CdTe/CdS flms to be a candidate
to work in thin-flm solar cells as an absorber layer.