Structural, optical and DFT studies of disodium phthalocyanine thin films for optoelectronic devices applications

Abstract

Theoretical and experimental investigations have been carried out on the structural and optical properties of disodium phthalocyanine (Na2Pc) thin films prepared using the thermal evaporation method. The optimized geometry structure, vibrational bands and HOMO-LUMO gap were predicted by density functional theory (DFT) computations. FTIR and XRD techniques were utilized to analyze the structural characteristics of Na2Pc thin films. XRD exhibited that the Na2Pc powder has α-polycrystalline nature with a triclinic structure, whereas the Na2Pc thin films have an amorphous structure. The optical properties of different thicknesses films were studied in the wavelength range of 200–2500 nm using the UV–Vis-NIR spectrophotometer. The absorption coefficient of the Na2Pc molecules showed four absorption bands in the UV–Vis region. The types of optical transitions were determined by applying the energy band model as an indirect allowed transition. The onset gap, optical gap and Urbach energy were estimated to be 1.31, 2.25 and 0.41 eV, respectively. The results of absorption coefficient and energy gap showed that the Na2Pc thin films can be utilized in optoelectronic device applications. The absorption index, k, and refractive index, n, were determined and found to be independent of the film thickness. The dispersion parameters have been evaluated according to a single oscillator model in the non-absorbing region of the spectrum.