Raman spectroscopy and optical constants of nanostructured oxovanadium(IV) tetraphenylporphyrin thin films

Abstract

Oxovanadium(IV) tetraphenylporphyrin (VOTP) thin films were prepared by thermal evaporation technique. The structural investigation and surface morphology of the VOTPP films were characterized by X-ray diffraction (XRD) and atomic force microscopy techniques (AFM). The XRD patterns used to extract lattice parameters, Miller indices, crystallite sizes and dislocation densities for VOTPP films are computed. While the micrographs of AFM of the films showed nanoparticles of cones-shaped structures turned to the agglomerations of nanostructures with the annealing temperature up to 250 °C. Raman spectroscopy of the as-deposited and annealed VOTPP films was recorded to identify their vibrational modes and functional groups and revealed thermal stability for these films. Moreover, UV–Vis absorption spectroscopy of the VOTPP films showed highly intense Soret band, two quasi-electronic Q-bands and two other L and N bands. The spectroscopic measurements of transmittance and reflectance of VOTPP thin films were recorded under different annealing temperatures, and from which, many optical constants and dispersive parameters were determined such as refractive index, absorption index, absorption coefficient, dielectric constant, oscillator energy and dispersion energy. The optical band gaps for as-deposited and annealed VOTPP films were calculated to be 1.9 and 1.69 eV, respectively. The annealing temperature induced changes significantly in the structural properties and spectroscopic characterizations and optical constants of VOTPP films. The present results revealed that VOTPP films could be utilized as promising absorbing layers in photovoltaics.