Effect of thermal annealing on the structural and optical properties of spin coated copper phthalocyanine thin films

• Thin films of copper phthalocyanine were prepared using spin coating technique.
• The optical and structural properties were studied before and after annealing.
• The films transformed from the metastable α-phase to the stable β-phase by annealing.
• The values of the optical band gap were redshifted by thermal annealing.
• The third order non-linear susceptibility was presented.

Low cost sol–gel spin coating was used to deposit copper phthalocyanine (CuPc) thin films on both fused quartz and glass substrate. The prepared films were studied before and after thermal annealing at 350 °C for 1 h in air. X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) were used to study the structural properties. From the structural characterization results, the films transformed from the metastable α-phase to the stable β-phase. Refractive index, absorption coefficient, and lattice dielectric constant were evaluated before and after annealing for the first time for spin coated CuPc thin films using spectrophotometric measurements in the spectral range 200–2500 nm. The values of the direct optical band gap of the as deposited film at 1.52 eV and 2.85 eV were redshifted to 1.4 eV and 2.42 eV for the annealed film. This shift is significant for near infrared photonics. The third order non-linear susceptibility was presented at lower photon energy for the CuPc films showing higher value for the annealed film.

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