Property enhancement of a close-spaced sublimated CdTe thin film by a post-growth activation step with CdCl2 and MgCl2

Abstract

The deposition parameters utilized during cadmium telluride (CdTe) film formation can regulate the microstructure of the absorber layer, which is crucial to photovoltaic conversion. In this study, borosilicate glass substrates are coated with CdTe thin films using the close-spaced sublimation approach under various argon pressures. At low pressure, a relative increase in grain size could be seen. A non-toxic magnesium chloride (MgCl₂)-based activation procedure of the CdTe thin film absorber layer has been followed and contrasted with the conventional cadmium chloride (CdCl₂) for solar cell applications. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), and ultraviolet-visible spectroscopy (UV-Vis) analyses of the impacts of the CdCl₂ and MgCl₂ activation treatment revealed the crystallization, morphology, composition, and optical attributes of the CdTe thin film. The Raman peak at 141 cm⁻¹ is accredited to a mixture of CdTe's transversal optic phonons after chloride treatment. The main diffraction peaks, corresponding to the (111), (220), and (311) cubic plane according to JCPDS card number 96-900-8841, appear prominently at 2θ = 23.8°, 39.29° and 46.91°, respectively. The SEM image reveals that crystals in the MgCl₂-treated CdTe thin film are quite highly textured. In addition, the treated CdTe samples show less absorbance than CdTe where the band gap varies between 1.48 and 1.56 eV and the refractive index ranges from 2.8–2.9, and the treatment effect is not that prominent. However, based on other structural and optical factors, it is evident that MgCl₂ is the ideal activator for industrial purposes because it is eco-friendly, non-toxic, affordable, and provides comparable efficiency to conventional toxic CdCl₂ activators.