Tailoring the optoelectronic properties of nanocrystalline β-H2Pc films via thermal annealing: Structural, morphological, and optical analyses

The present study extensively investigates the optical and structural properties of β-H2Pc thin films before and after annealing at temperatures of 373, 423, 473, 523, and 573 K/1 h, enabling the design of efficient organic-based devices. The mean crystallite size was calculated from XRD and found to be 8.5 nm at 300 K, which increased as the annealing temperature increased, confirming the crystallinity improvement upon annealing. In addition, the SEM images revealed that the grain size increased with increasing annealing temperature. The FTIR results confirmed the high thermal and chemical stability upon annealing. Furthermore, increasing the annealing temperature leads to a decrease in the transmittance spectrum and an increase in the reflectance spectrum. The results revealed a decrease in the optical band gap of β-H2Pc films from 1.472 eV to 1.406 eV for the onset gap and from 2.44 to about 2.21 eV for the fundamental gap with increasing annealing temperature to approximately 573 K. Moreover, the nonlinear optical parameters show an increase with higher thermal treatment temperatures. The annealing process has a significant impact on the optical and structural properties, leading to noticeable variations at specific annealing temperatures.