Comprehensive optical characterization of organic thin films for OLED applications via spectroscopic ellipsometry

In this study, spectroscopic ellipsometry was employed to characterize the optical properties of 19 different organic thin films used in the fabrication of organic light-emitting diodes (OLEDs). The films were deposited via thermal evaporation onto quartz and soda lime float glass substrates coated with a SiO₂ buffer layer and indium tin oxide (ITO). The analysis included a range of organic compounds, from widely studied materials such as CBP (4,4′-Bis(N-carbazolyl)-1,1′-biphenyl) to less-explored compounds such as TAZ (3-(Biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole), PO-T2T ((1,3,5-Triazine-2,4,6-triyl)tris(benzene-3,1-diyl)tris(diphenylphosphine oxide)), CzSi (9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole), and NBphen (2,9-Dinaphthalen-2-yl-4,7-diphenyl-1,10-phenanthroline). Attention was given to the influence of substrate material on the complex refractive index - specifically, the refractive index (n) and extinction coefficient (k) - across a broad spectral range (210–1690 nm, 0.7–5.9 eV). The results reveal critical insights into substrate-dependent variations, including the presence of refractive index gradients and anisotropic optical behavior in selected organic thin films.