Effect of temperature on stacking orientations of zinc phthalocyanine thin films

This paper reports the structural and optical properties of zinc phthalocyanine (ZnPc) thin films, prepared by thermal evaporation method, and their stacking dependence on the substrate temperature. The thickness of the films was measured by a quartz crystal monitor. X-ray diffraction analysis of the vacuum evaporated ZnPc films identified a phase transformation of metastable alpha-ZnPc phase to stable beta-ZnPc phase due to variation in the substrate temperature. The crystallite size (D), dislocation density (delta) and strain (epsilon) were calculated. The transmittance and absorbance spectra were recorded in the wavelength range 300-2500 nm using a UV-vis spectrophotometer. As the temperature was increased from room temperature to 200 degrees C, the band gap energy was decreased from 1.82 eV to 1.67 eV. The phase transformation was also confirmed by optical studies.