Influence of NH 4 Cl treatment on physical properties of CdTe thin films for absorber layer applications

Abstract

The physical properties of electron beam evaporated and chlorine-passivated CdTe thin films are investigated and the influence of NH4Cl treatment on these properties is studied. X-ray diffraction, UV–Vis spectrophotometry, energy-dispersive spectroscopy, atomic force microscopy, and a source meter were used to investigate the physical properties, which were optimized by varying the temperature of the treatment after NH4Cl activation. Structural analysis reveals that the crystallinity is increased at lower annealing temperature while a partial phase transition and oxidation are observed at higher annealing temperature. The absorbance is high in the visible region, and a red shift is observed at higher wavelength, while the direct bandgap is tuned by chlorine activation. The deposition of thin films and chlorine treatment were confirmed by elemental analysis. Surface topographical study reveals that the average roughness is increased with an annealing temperature up to 320 °C, while the I-V characteristics indicated ohmic nature of the contacts. The optimized results show that the NH4Cl-treated CdTe films annealed at 320 °C may be applicable as an absorber layer in solar cells.