Determination of the complete set of optical parameters of micron-sized polycrystalline CH₃NH₃PbI_3−xCl_x films from the oscillating transmittance and reflectance spectra

The complete set of optical parameters of micron-sized polycrystalline CH₃NH₃PbI_3−xCl_x films deposited by the vacuum co-evaporation of lead iodide and methylammonium chloride is determined by analysis of oscillating optical transmittance and reflectance spectra in the wavelength range 400–1000 nm. It is shown that for a medium and weak absorption region the envelope method is valid for the extraction of refractive index, extinction and absorption coefficient when is using only transmittance spectra. As well thickness of the film is determined from transmittance and reflectance spectra with interference-effect. The absorption coefficient for the strong absorption region and optical band gap (direct transition at E _opt=1.62 eV) are calculated based on transmittance and reflectance spectra by using conventional approximated formulas. (paper)