Abstract
In recent years, organic semiconductors attracted a lot of attention due to their potential use in organic electronics such as light emitting diodes (OLEDs), photovoltaics and photodetectors. Tris‐(8‐hydroxyquinoline)‐aluminium(III) (Alq~3~) and N,N_‐di‐[(1‐naphthyl)‐N,N‐diphenyl]‐(1,1‐biphenyl)‐4,4‐diamine (α‐NPD) are among the most commonly used electron transport and hole‐transport materials in OLEDs, respectively. In this work, Alq~3~ and α‐NPD thin films with various thickness values were deposited onto Si and glass substrates by organic vapour phase deposition (OVPD). Spectroscopic Ellipsometry (SE) in a wide spectral region from the infrared (IR) (900–4000 cm^−1^) to the near infrared–visible–far ultraviolet (NIR–Vis–fUV, 0.7–6.5 eV) has been implemented in order to investigate the influence of the thickness on their optical and structural properties. From the analysis of the SE spectra, we estimated the band gap values, the optical absorptions and the vibrational response of the materials. The results showed that the α‐NPD thin films show four characteristic absorptions and the optical response of the material is independent of the films thickness. Finally, in case of Alq~3~, the material shows a band gap at 2.7 eV and three characteristic absorptions.