Optical and charge carrier transport properties of polymer light emitting diodes based on MEH-PPV

Optical properties of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) films have been studied by analyzing temperature dependent photoluminescence spectra. Charge carrier conduction processes and dielectric properties of ITO/MEH-PPV/Al device have been investigated using current density–voltage (J–V), ac impedance and capacitance–voltage (C–V) characteristics. Charge carrier conduction at lower voltages is ohmic and switches to space charge limited current (SCLC) conduction with exponential trap distribution at higher voltages (above 3 V). From the temperature dependent impedance characteristics an activation energy of 0.42 eV has been extracted. The conduction mechanism revealed from J–V characteristics has been correlated with impedance characteristics. The behavior of trap charges has been studied using frequency dependent C–V characteristics. From the detailed analysis of C–V characteristics, ionized acceptor density NA, diffusion potential VD and the width of the depletion layer w have been extracted.