Impact of low temperature annealing on structural, optical, electrical and morphological properties of ZnO thin films grown by RF sputtering for photovoltaic applications

• The physical properties of polycrystalline sputtered ZnO thin films are carried out.
• XRD pattern reveals that the films have wurtzite structure with orientation (1 0 0).
• The optical band gap varies in the range 3.30–3.52 eV with thermal annealing.
• The I–V characteristics show that the films exhibits approximately ohmic behavior.
• The SEM studies show that films are uniform, homogeneous and free from crystal defects.

This paper presents effect of low temperature annealing on the physical properties of ZnO thin films for photovoltaic applications. The thin films of thickness 50 nm were grown on glass and indium tin oxide (ITO) coated glass substrates employing radio frequency magnetron sputtering technique followed by thermal annealing within low temperature range 150–450 °C. These as-grown and annealed films were subjected to the X-ray diffraction (XRD), UV–Vis spectrophotometer, source meter and scanning electron microscopy (SEM) for structural, optical, electrical and surface morphological analysis respectively. The compositional analysis of the as-grown ZnO film was also carried out using energy dispersive spectroscopy (EDS). The XRD patterns reveal that the films have wurtzite structure of hexagonal phase with preferred orientation (1 0 0) and polycrystalline in nature. The crystallographic and optical parameters are calculated and discussed in detail. The optical band gap was found in the range 3.30–3.52 eV and observed to decrease with annealing temperature except 150 °C. The current–voltage characteristics show that the films exhibit approximately ohmic behavior. The SEM studies show that the films are uniform, homogeneous and free from crystal defects and voids. The experimental results reveal that ZnO thin films may be used as alternative materials for eco-friendly buffer layer to the thin film solar cell applications.

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