Understanding the grain growth mechanism in CdS thin films by CdCl2 treatment and thermal annealing evolution

Abstract

In order to upgrade the crystallinity and minimize the detrimental effect of grain boundaries and crystals defects in thin films and solar cells concerned, an approach of chloride treatment to polycrystalline Cd-based thin films could be undertaken. Therefore, in present study, the micro-structural, morphological, optical, electrical properties of post chloride-treated CdS thin films are explored where the CdS films (having thickness 200 nm) are fabricated on glass and ITO substrates using thermal evaporation technique. The X-ray diffraction results reveal that the CdS films are polycrystalline in nature having mixed hexagonal and cubic crystalline phases with (220)C preferred orientation where the crystallite size is found to improve with CdCl2 treatment. The CdCl2 treated films showed the prominent ohmic character owing to linear behavior of I–V plots. The direct optical energy band gap is found to be in the range of 2.09–2.38 eV with chloride treatment where the transmittance is observed higher in longer wavelength region. The deposition of thin films and chloride treatment are confirmed by elemental analysis. The grain growth mechanism is demonstrated which is responsible for change in physical properties and recrystallization. The surface roughness is varied and grain size is enhanced as revealed by AFM and FESEM images, respectively. The optimized findings show that 100 °C air annealed CdS thin films could be used as an efficient window layer to the Cd-based solar cell devices.