Improvement of composition of CdTe thin films during heat treatment in the presence of CdCl2

CdCl 2 treatment is a crucial step in development of CdS/CdTe solar cells. Although this processing step has been used over a period of three decades, full understanding is not yet achieved. This paper reports the experimental evidence for improvement of composition of CdTe layers during CdCl 2 treatment. This investigation makes use of four selected analytical techniques; Photo-electro-chemical (PEC) cell, X-ray diffraction (XRD), Raman spectroscopy and Scanning electron microscopy (SEM). CdTe layers used were electroplated using three Cd precursors; CdSO 4 , Cd(NO 3 ) 2 and CdCl 2 . Results show the improvement of stoichiometry of CdTe layers during CdCl 2 treatment through chemical reaction between Cd from CdCl 2 and elemental Te that usually precipitate during CdTe growth, due to its natural behaviour. XRD and SEM results show that the low-temperature (~85 °C) electroplated CdTe layers consist of ~(20–60) nm size crystallites, but after CdCl 2 treatment, the layers show drastic recrystallisation with grains becoming a few microns in size. These CdCl 2 treated layers are then comparable to high temperature grown CdTe layers by the size of grains.