Optical and Electrical Properties of Some Organic Thin Films for Optoelectronic Applications

Organic semiconductor thin films of bis-(2-methyl-8-quinolinolato)-4-(Phenyl-phenolato) -aluminium-(III) (BAlq), N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB), and tris-(8-hydroxyquinoline) aluminum (Alq) were prepared by the vacuum sublimation technique. The optical properties in the UV-visible region of the thin films were investigated by optical transmittance and absorbance spectra. The optical energy gaps were obtained from direct allowed transitions at room temperature by Tauc's law. The Urbach energy and the slope of Urbach edge were estimated by the Urbach-edges method, respectively. Furthermore, the current-voltage characteristics of organic thin films were analyzed, and the different slopes in the lower and higher voltage regions were observed. From the experimental studies, the effective carrier mobility, free carrier density, and electrical conductivity were also evaluated respectively.