Complex dielectric function of H-free a-Si films: Photovoltaic light absorber

•Amorphous silicon layers were grown using sputtering deposition.•Cody-Lorentz model was adopted to calculate the complex refractive index.•It has found the real and imaginary parts of the dielectric function.•The study highlights the sensitivity to film uniformity.•Amorphous silicon could serve as a precursor for fabricating a light absorber.