Morphology and optical properties of E143 food dye organic semiconductor for spectrally selective window applications

Organic semiconductor thin films of E143 food dye (C37H34N2Na2O10S3) were prepared using a spin coating technique with different thicknesses varying from 80 to 240 nm. The studies of film morphology by scanning electron microscope (SEM) and atomic force microscope (AFM) showed the best homogeneity and optical quality for 240 nm film thickness. The optical constants and interband transitions were characterized by absorption, transmission, and reflection spectra in the range (190–2700 nm). Based on optical theories, the absorption edges showed directly allowed band gap transitions between bonding and antibonding energy levels; also, the Dielectric constant, dielectric loss, and dissipation factor were calculated and discussed. The calculated values of the average oscillator strength and dispersion were consistent with the values reported by Wemple–DiDomenico model and for semiconductor materials. The optimized film thickness was applied to FTO glass for spectrally selective windows (SSW) applications. The spectroscopic results implied the applicability of E143 food dye thin films for energy efficient windows as it lowers the amount of solar energy that comes inside buildings particularly in sunny countries like KSA.