Admittance Analysis in (PPE-PPV) Polymer (AnE-PVstat) Light Emitting Diodes

Abstract

In this work, admittance analysis of organic light emitting diode (OLED) (anode/active layer/cathode) was performed at room temperature within the frequency range of 1 kHz-1MHz to find out transport properties of both injected carriers from each side. Moreover, by proper chosen metals, electron or hole only OLED devices were prepared and the measurement was resumed to identify the governed transport path of injected carrier. Mobility of injected carriers followed the Poole-Frenkel type conduction mechanism and distinguished in the frequency range due to the difference of transit times in admittance measurement. Beginning of light output and onset of negative capacitance took place at the turn-on voltage (or flat band voltage), 1.8 V, which was the difference of energy band gap of polymer and two barrier offsets between metals and polymer. The proposed analytical model for admittance, derived for the frequency dependent space charge limited behavior leading negative capacitance issues, was applied on the measured data for the present OLED device.