Exploring structural, linear, nonlinear optical, and electrical properties of PMMA–ZnTTBPc composites

Abstract

In this work, poly(methyl methacrylate) (PMMA)–zinc 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (ZnTTBPc) composite films containing 0.2–1.2 wt% ZnTTBPc were fabricated by spin coating and characterized using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), UV–Vis–NIR spectroscopy, and current–voltage (I–V) measurements. XRD and SEM analyses confirmed the predominantly amorphous nature of the films and revealed concentration-dependent morphological changes with increased aggregation at higher ZnTTBPc loadings. Optical investigations showed a gradual reduction in the optical band gap of PMMA with increasing ZnTTBPc content, accompanied by systematic variations in the characteristic Q- and B-band transition energies. The refractive index, extinction coefficient, and related optical constants increased with dopant concentration, while the dispersion behavior was analyzed using the Wemple–DiDomenico single-oscillator model. The estimated third-order nonlinear optical susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂), derived from linear optical parameters, increased systematically with ZnTTBPc concentration. Electrical characterization of Au/PMMA–ZnTTBPc/FTO heterostructures showed an increased rectification ratio and reduced series resistance following ZnTTBPc incorporation. Analysis of the current–voltage characteristics using empirical transport models suggested that the observed electrical behavior can be described by Ohmic, trap-influenced space-charge-limited conduction (SCLC)-like, Poole–Frenkel-type, and Schottky-type formalisms over different voltage ranges. Overall, ZnTTBPc incorporation systematically modified the structural, optical, and electrical characteristics of.