Study of Structural, Optical and Electrical Properties of CuSe2/CdS/ITO Thin Films Deposited by Thermal Evaporation Technique for Solar Cells Applications

Abstract

Abstract In this study, first the alloy of copper selenide was prepared by quenching technique. After that copper selenide and cadmium sulphide thin films are prepared by using thermal evaporation technique. The thin films have been grown on clean glass and ITO substrates. The annealing effects on the structural, optical and electrical properties of the films which have been studied. The results of XRD showed that the copper selenide alloy was polycrystalline in nature with multiphase of copper selenide, the dominate phase was CuSe2 with cubic structure and preferred orientation (221). The cadmium sulfide films were single crystalline, have cubic structure with orientation (111) plane for as-deposited and annealed films. Copper selenide films show polycrystalline nature for as-deposited and annealed films, the Cu3Se2 phase with tetragonal structure and preferred orientation (101) plane was dominate in the as-deposited film while the CuSe2 phase with cubic structure and preferred orientation (221) plan was dominate in annealed film. "Scherrer’s formula" has been used to calculate the crystallite size and it is found increases after annealing for both films. ""AFM" outcomes show that increase in surface roughness and (RMS) for both annealed films, in addition the grain size of cadmium sulphide film increases in annealing but decreases for copper selenide film. SEM results show that the copper selenide powder have a compact structure composed of single type. The absorbance and transmittance curves were recorded in the range of (400- 1100) nm to investigate the optical characteristics. The results have shown that the cadmium sulphide and copper selenide films have a good transmittance in visible and NIR region. The absorption coefficient and refractive index were calculated too. The energy gap for allowable direct electronic, transition was estimated using Tauc’s model. The energy gap was decrease from (2.45 eV) to (2.41 eV) for cadmium sulphide thin film when annealed, and for copper selenide was increase from (2.27 eV) to (2.32 eV) after annealed. The electrical properties included D.C, hall effect measurements, and (I-V) characteristic of solar cell. From D.C. measurements, It has found that the D.C conductivity of cadmium sulphide thin film was increase after annealing while decrease for copper selenide thin film after annealing. All films have two transport mechanisms of free carriers and there was two activation energies for as- deposited and annealed films. Hall measurement results showed that the thin films of cadmium sulphide are n-type while copper selenide thin films are p-type. On the other hand, “Voc, ISC, Rs , Rsh , FF and efficiency” of the solar cell have been measured. The solar cell parameters were found by using (I-V) tester system under illumination. The results show that no efficiency found for copper selenide/ cadmium sulphide /ITO solar cell.