Thermal annealing effects on optical and dielectric properties of TiOPc thin films for optoelectronic and photonic applications

Abstract Titanyl phthalocyanine (TiOPc) is a metal phthalocyanine compound with interesting electronic and catalytic properties, making it useful in various applications. This study investigates the effects of thermal annealing on the optical and dielectric properties of vacuum-evaporated TiOPc films. The optical and structural characteristics were examined before and after annealing. FTIR spectra show a correlation between the peak positions of the films before and after the annealing process. Additionally, the spectra of the annealed sample show a decrease in C=O and the formation of a coordination bond between the Ti dopant and the phthalocyanine molecule. X-ray diffraction shows an amorphous behavior before and after annealing for TiOPc films. The AFM images show the presence of peaks and valleys of varied sizes. This leads to enhanced light trapping and scattering, improving light absorption and optical properties of the film. Thermal annealing at 473 K for 2 h resulted in a significant reduction in the optical energy gap, with E g1 decreasing by approximately 7% (from 1.58 eV to 1.47 eV) and E g2 by about 6% (from 3.0 eV to 2.83 eV), which indicates the thermal stability of these films. Moreover, the real part of dielectric constants reached appreciable improvements of about 30% at low frequencies. These changes are ascribed to the decreased structural defects and enhanced molecular ordering induced by annealing. The thermal stability of TiOPc films and improvement in the performance of optoelectronic devices such as photodetectors and optical switches by applying TiOPc films can be understood from these explorations. Moreover, the simple and cost-effective vacuum evaporation and annealing fabrication enable large-scale industrial production that would be attractive for application engineers to fully utilize these films in practice.