Study on the Optical and Electrical Properties of Organic Semiconductor Thin Films for OLEDs

Organic semiconductor thin films of aluminum (III) bis(2-methyl-8-quninolinato)-4-phenylphenolate (BAlq), alpha-naphthylphenylbiphenyl amine (NPB), and tris(8-hydroxy-quinoline) aluminum (AlQ) for organic light-emitting diodes (OLEDs) were deposited by the vacuum sublimation technique. The optical properties in the UV-visible region of the thin films were investigated by optical transmittance and absorption spectra. The band gaps were obtained from direct allowed transitions at room temperature by means of the Tauc plots. The Urbach energy and the slope of Urbach edge were evaluated respectively according to the Urbach-edges method. The thin film devices of sandwich structure were fabricated by using these organic semiconductor materials, in addition, the effective carrier mobility, free carrier density, and electrical conductivity of the thin films were calculated in terms of the measured current-voltage characteristics of the devices.