Effect of titanyl phthalocyanine doping on opto-electrical properties of Alq₃ thin films

Abstract

The titanyl phthalocyanine (TiOPc) was doped in tris (8-hydroxy quinolinato) aluminum (Alq₃) with concentration of 1, 2 and 3 % by weight. The thin film of undoped and doped Alq₃ was studied extensively for optical and electrical properties. The refractive index of the studied material was found in the range of 1.5–2.07 for 300–1000 nm wavelength. The Urbach tail energy decreases by increase of doping concentration. The PL quenching ratio increases with doping that attribute charge transfer from Alq₃ to the TioPc. The electrical properties of the thin film were studied by impedance spectroscopy over a frequency range of 100 Hz–1 MHz. The undoped and doped Alq₃ shows single relaxation process. The Cole–Cole plots of undoped and doped device can be represented by a single parallel resistance R _P and capacitance C _P network with a series resistance R _S . The value of R _P and C _P at zero bias are ~146 kΩ, 87 kΩ, 814 Ω and 22 kΩ and 68, 9, 30 and 29 nF for undoped, 1, 2 and 3 % doping, respectively. The resistance R _P decreases with applied bias whereas the capacitance C _P remains almost constant. At high frequency, the AC conduction of the film follows the universal power law and the onset frequency increases with increasing bias voltages.