Tuning of structural and optical properties of 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine thin films as a promising photovoltaic absorber material

摘要： Thin films of 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (H2TPyP) dye have been prepared using thermal evaporation technique. The crystal structure has been studied using the field emission scanning electron microscopy and X-ray diffraction pattern. The structure investigation of H2TPyP exhibited a polycrystalline nature in the form of powder while the thin films revealed a nanocrystalline structure. The optical features of H2TPyP thin films have been examined using spectroscopic measurements of the absorbance, the transmittance, and the reflectance of those films within spectral range of 200–2500 nm. From such measurements, the optical constants, the dispersion parameters, and the related optical variables were calculated and interpreted. The absorbance spectra of the films revealed the four quasi-electronic states named Q-bands and more intense Soret (B) band located at UV–visible spectral region. In addition to other weaker bands labeled M, N, and L observed at UV spectrum. The electronic inter-band transition for the H2TPyP thin films revealed an indirect allowed transition with the onset optical band gap Eg of 1.78 eV. Urbach tail energy EU was observed beyond the Eg and was found to be 0.36 eV. Furthermore, the energy loss functions, dielectric constants and optical conductivities were also studied.