OPTICAL PROPERTIES OF THERMALLY EVAPORATED METAL-FREE PHTHALOCYANINE (H2Pc) THIN FILMS

Abstract

The optical properties of metal-free phtalocyanine ( H 2 Pc ) in thin film form is investigated. X-ray diffractograms of the ( H 2 Pc ) powder show that it has a α-polycrystalline form with a monoclinic structure. The thermal evaporation of ( H 2 Pc ) powder leads to α-polycrystalline films, oriented preferentially to the (001) plane. After annealing at 623 K for two hours, a mixture of α- and β-phases is formed on an amorphous background. The optical properties of ( H 2 Pc ) thin films have been studied using spectrophotometeric measurements of transmittance and reflectance in the range 200–2200 nm for a different film thickness. The refractive index and the absorption index show independence on the film thickness. The refractive index shows anomalous dispersion in the region of the fundamental absorption edge. The absorption measurements show the characteristic splitting of the Q-band and ΔQ is obtained as 0.22 eV. The absorption coefficient in the absorption region reveals indirect transitions. The fundamental and the onset energy gap are determined as 2.74 eV and 1.55 eV, respectively.