Impact of thermal annealing on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

• The CdTe films have zinc-blende structure with preferred orientation (111).
• Optical band gap is found to decrease from 1.64 eV to 1.48 eV with thermal annealing.
• The as-grown films are uniform, homogeneous and free from crystal defects.
• The surface roughness is increased with annealing temperature.

A study on impact of post-deposition thermal annealing on the physical properties of CdTe thin films is undertaken in this paper. The thin films of thickness 500 nm were grown on ITO and glass substrates employing thermal vacuum evaporation followed by post-deposition thermal annealing in air atmosphere within low temperature range 150–350 °C. These films were subjected to the XRD, UV‐Vis NIR spectrophotometer, source meter, SEM coupled with EDS and AFM for structural, optical, electrical and surface topographical analysis respectively. The diffraction patterns reveal that the films are having zinc-blende cubic structure with preferred orientation along (111) and polycrystalline in nature. The crystallographic parameters are calculated and discussed in detail. The optical band gap is found in the range 1.48–1.64 eV and observed to decrease with thermal annealing. The current–voltage characteristics show that the CdTe films exhibit linear ohmic behavior. The SEM studies show that the as-grown films are homogeneous, uniform and free from defects. The AFM studies reveal that the surface roughness of films is observed to increase with annealing. The experimental results reveal that the thermal annealing has significant impact on the physical properties of CdTe thin films and may be used as absorber layer to the CdTe/CdS thin films solar cells.

The physical properties of polycrystalline CdTe films are investigated with thermal annealing treatment and results indicate that annealed films may be used as absorber layer in CdTe solar cells.Figure optionsDownload as PowerPoint slide