Controlling the crystallite size and influence of the film thickness on the optical and electrical characteristics of nanocrystalline Cu 2S films

Abstract

In this work, Cu 2S nanocrystalline films have been successfully prepared using dip-coating technique. The stoichiometry and the structural characteristics of the prepared films were characterized by energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), respectively. The surface morphology of the deposited Cu 2S film was studied using both the scanning electron microscopy (SEM) and the atomic force microscopy (AFM). The SEM and AFM images indicate that the prepared Cu 2S films are characterized by a well-dispersed and highly dense with spherical like-shaped aggregates of size in the nano scale. The optical absorption measurements indicate that the Cu 2S nanoparticles have a direct band gap of 2.92 eV. The dispersion and absorption parameters such as the dispersion energy, oscillating energy, real and imaginary dielectric constants and dissipation factor were calculated within a wide wavelength range of the spectrum that indicates the suitability of the deposited films as solar absorber using this technique. The dark electrical resistivity ( ρ) measurements were carried out at different temperatures in the range 312–440 K. These results confirm the semiconducting characteristic of the prepared Cu 2S films. Moreover, two activation energies were obtained that indicate the presence of two dominating conduction mechanisms in these temperature ranges. The bulk electrical resistivity ( ρ B) and the mean free path ( l 0) of charge carriers were estimated from the resistivity-thickness dependence. The heterojunction device of n-ZnCdS/p-Cu 2S behaves good rectifying property. The photovoltaic characteristic of the heterojunction device using the current–voltage characteristic under illumination of 100 mW/cm 2 was also observed. Discussion of the obtained results and their comparison with the previous published data were also considered.