# Optimized electrical and physiochemical properties of cadmium telluride thin films via copper chloride treatment for photovoltaic applications

## TL;DR

This paper explores how copper chloride treatment improves the properties of cadmium telluride thin films for solar cell applications.

## Contribution

The study introduces an optimized CuCl₂ treatment method that enhances CdTe thin films' performance for photovoltaics.

## Key findings

- A 0.005 M CuCl₂ concentration achieves optimal p-type activation and minimizes Cu diffusion.
- CuCl₂ treatment increases microstrain and refines grain size, as shown by XRD and FESEM analyses.
- The treatment improves carrier transport and retains zincblende crystallinity without secondary phases.

## Abstract

An in-depth examination was undertaken on the structural, optical, and electrical alterations of CdTe thin films exposed to CuCl₂ post-treatment with different molar concentrations. The films were prepared using the close-spaced sublimation (CSS) approach. The CuCl₂ treatment at 390 °C in ambient air had significant impacts on the crystallographic orientation, lattice properties, and carrier concentration of CdTe films. The full width at half maximum (FWHM) increased from 0.0038 radians at 0.0005 M CuCl₂ to 0.0068 radians at 0.05 M, indicating grain refinement and increased microstrain at higher Cu concentrations, confirming a significant zincblende (111) preferred orientation as the X-ray diffraction (XRD) research reported. The inclusion of Cu and the resulting lattice deformation demonstrate a significant relationship with the evolution of crystallite size and dislocation density, indicating a regulated interaction between the dopant and the lattice throughout the examined molarity range. A comprehensive evaluation of structural, optical, morphological, and electrical properties indicates that a CuCl₂ concentration of 0.005 M achieves an optimal balance, facilitating effective p-type activation while preventing excessive Cu diffusion, which is associated with increased microstrain, decreased mobility, and heightened recombination at elevated dopant concentrations. XRD analysis confirms the retention of zincblende crystallinity without the formation of secondary phases, while optical measurements demonstrate stable band-gap behaviour, indicating minimal electronic distortion. Complementary FESEM and EDX analyses reveal enhanced grain coalescence and a reduction in grain-boundary density, which together facilitate improved carrier transport. The synergistic enhancements position the CuCl₂ solution-based treatment, especially at 0.005 M, as an effective and environmentally friendly alternative to traditional CdCl₂ activation, directly influencing the formation of ohmic contacts and the performance of CdTe thin-film.