Understanding Grain Growth Mechanism in Vacuum Evaporated CdTe Thin Films by Different Halide Treatments: An Evolution of Ion Size Impact on Physical Properties for Solar Cell Applications

In the present study, detailed investigation on postdeposition halides treatment using CdCl2, CdI2, MgF2, MgCl2 and MgI2 is undertaken over thermally evaporated CdTe films. As-deposited films are subjected to halide treatment and subsequent annealing at 385 & DEG;C. Halide activation induced grain growth mechanism is presented along with anions and cations roles on change in films properties and formation of different complexes. XRD patterns of all CdTe thin films exhibited polycrystalline nature with preferential cubic phased (310) plane except for CdI2 treated films where preferred reflection is appeared corresponding to (220) plane. Grain growth is observed with treatment employing amicable estimation tools. All films have a conspicuous ohmic character owing to linear I-V plots. Optical study reveals that CdCl2 treated CdTe films have higher absorbance and optical energy band-gap is measured out in the range 1.42-1.53 eV with halide treatment. Surface topography and PL study revealed to variations in surface roughness and photoluminescence peaks intensity with halide treatments. Film growth and treatment are validated by EDS analysis and FESEM images demonstrated explicit grain growth. Findings warrant amazing role of halide activation on film properties and CdCl2 is found a suitable surface treatment agent to CdTe films in order to develop better devices.