Dependence of the Dielectric Properties of Organic Light-Emitting Diodes with a PTFE Hole-Injection Layer on the Applied Voltage

Abstract

Dependence of the Dielectric Properties of Organic Light-Emitting Diodes with a PTFE Hole-Injection Layer on the Applied Voltage Young-Hwan Lee, Weon-Jong Kim, Kyung-Soon Cho, Jong-Yong Lee and Jin-Woong Hong Department of Electrical Engineering, Kwangwoon University, Seoul 139-701 Tae-Wan Kim Department of Physics, Hongik University, Seoul 121-791 (Received 12 December 2007) The dependences of the dielectric properties of organic light-emitting diodes on applied AC voltage were studied in a structure of indium tin oxide(ITO)/hole injection layer, polytetra uorethylene (PTFE)/Alq3(tris(8-hydroxyquinoline)aluminum)/Al. The hole-injection material PTFE, which is a uoric-system polymer, was deposited at a deposition rate of 0.1 0.2 A/s to a thickness of 2 nm and the Alq3 was deposited at a deposition rate of 1.3 1.5 A/s under high vacuum (5 10 6 Torr) to a thickness of 100 nm. To investigate the dielectric properties of these devices, we measured the complex impedance, which showed that the impedance decreased as the applied voltage was increased and that the dielectric loss exhibited a peak at a certain voltage. A Cole-Cole plot of the impedance was plotted and analyzed. As the applied voltage was increased, the radius of the Cole-Cole plot decreased. The interface resistance between the ITO and the double layer was about 35 in the device with a 100-nm-thick Alq3 layer. PACS numbers: 73.61.Ph, 77.22.Gm