Investigating the salient features of CdCl2 treatment for performance enhancement in CdS/CdTe photovoltaics

A crucial step in the fabrication of CdTe solar cells is to anneal the CdS/CdTe stack in the presence of CdCl 2 , a process known as ‘activation’. This transforms a low-efficiency (2%) cell into an efficient (η>10%) one. This activation offers some additional benefits, including electrical and structural modifications in CdS and CdTe. Despite being utilized for over three decades, a comprehensive understanding of this process remains elusive. In the present work, a comparative study of junction activation in CdS/CdTe solar cells with as-deposited, heat-treated, and CdCl 2 -treated CdTe films is presented. The microstructural and optoelectronic properties of electrodeposited CdTe films are investigated and optimized through CdCl 2 treatment and correlated with the surface morphology. The results of this study provide empirical evidence that CdCl 2 treatment enhances the structural, optical, and morphological properties of the CdTe layer compared with untreated and heat-treated layers in ambient air. The prepared samples have been characterized by some well-known analytical techniques, such as X-ray diffraction (XRD), UV-Vis spectroscopy, photoluminescence (PL), Raman spectroscopy, Fourier transformation infra-red (FT-IR) spectroscopy, field effect scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) analysis, and high-resolution transmission electron microscopy (HR-TEM). The XRD spectra show increased peak intensity with CdCl 2 treatment compared with the other two samples. FE-SEM images confirm the ability of CdCl 2 treatment to regulate CdTe shape and grain size. The bandgap, estimated from UV-Vis analysis, changes from 1.46 eV to 1.43 eV. HR-TEM images reveal a significant improvement in the quality of the CdTe film after CdCl 2 treatment. The current density-voltage (J-V) characteristic curves are plotted to examine the PV parameters of the fabricated CdS/CdTe cell, and the device efficiency is calculated at 10.8%. Based on these experimental findings, the CdCl 2 heat treatment emerges as a highly effective method for the electrodeposition (ED) of CdTe solar cells.