Impact of silver dopants on structural, morphological, optical, and electrical properties of copper-zinc sulfide thin films prepared via sol-gel spin coating method

In recent days, Eco-friendly nano-composite thin film employed as an absorber layer in solar cells is one of the most worthy kind of industrial semiconductors and a variety of optoelectronics and optical device applications. Thus, nano-composite samples of copper-zinc sulfide (Cu-Zn-S) embedded with silver dopants (Ag) were perfectly synthesized using 280 degrees C temperature and low-cost sol-gel spin coating technique without sulfurization. For this objective, several films like pristine (S-0) and Ag-doped Cu-Zn-S with different Ag concentrations 0.5% (S-1), 1% (S-2) and 2% (S-3) were deposited on various kinds of substrates like glass, n-type and p-type silicon (Si) with 5 and 8 layer thicknesses. The impact of Ag concentration and the thickness of the prepared film on the surface morphology, structural, electrical, and optical properties of the deposited films on glass substrates were elaborated. It was found that both pristine and Cu-Zn-S films doped with various concentrations of Ag depict the polycrystalline structure of hexagonal and cubic crystal structure using X-ray diffraction. The images of the SEM (scanning electron microscopy) displayed excellent compatibility, homogeneous spreading with a smooth uniform surface, and cover all the areas of the substrates, especially the 1% Ag/Cu-Zn-S film with the structure of less porosity. The results of ICP-OES (inductively coupled plasma-optical emission spectroscopy) and EDS (energy dispersive spectroscopy) were investigated to identify the composition of the forming elements. The optical properties of pristine and Ag-doped films with 5 and 8 layer thicknesses were reported. It was found that for 5 layer deposition at 280 degrees C, the optical bandgap energy (E-g) reduces from 2.29 eV (S-0) to 2.09 eV at 2% Ag/Cu-ZnS (S-3) films. While for 8 layer deposition, the E-g decreases from 2.16 eV (S-0) to 1.91 eV at 2% Ag/Cu-Zn-S (S-3) films. Hence it can be concluded that the Eg decreases with increasing the thickness of the film, which is in agreement with the achieved results in the literature. In addition, it was observed that the 1% Ag/Cu-Zn-S (S2) film has the lowest resistivity value of 0.66 Omega cm at 280 degrees C. From all measurements obtained by depositing films on glass substrates, we select the best films to be deposited on n- and p-types Si substrates to study the impact of the n- and p-types silicon substrates on the properties of our films. We also calculated the values of the index of refraction (n), high frequency and optical static dielectric constants (epsilon(infinity), epsilon(o)) of deposit films on Si and glass substrates through the calculation of Eg as a function of the silver concentrations.