Effect of titanyl phthalocyanine doping on opto-electrical properties of Alq 3 thin films

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 RP and capacitance CP network with a series resistance RS. The value of RP and CP 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 RP decreases with applied bias whereas the capacitance CP 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.