Determination of localized trap parameters in organic semiconductors using charge based deep level transient spectroscopy (Q-DLTS)

¹ Laboratoire de Physique Cristalline, Institut des Matériaux Jean Rouxel, 2 rue de la Housssinière 44322 Nantes Cedex 3, France
² Department of Electronic and Electrical Engineering, University College London - Torrington Place, London WC1E 7JE, UK

Corresponding author: nguyen@cnrs-imn.fr.

Received: 4 July 2003
Accepted: 10 February 2004
Published online: 15 July 2004

Abstract

In organic light emitting diodes (OLEDs), localized traps within the band gap of the organic semiconductor play a fundamental role in the light emission process. Trapped charge carriers cannot recombine efficiently and therefore do not contribute to the emission. The determination of the trap parameters in the emitting layer is especially important in the evaluation of the efficiency of such devices. We have investigated the trap parameters in some organic semiconductors using the Charge-Based Deep Level Transient Spectroscopy (Q-DLTS) technique. Examples are given in poly(p phenylene vinylene) or PPV and 4, 4'-bis(4-dimethylaminostryryl) or DMASB, for which the trap level, the trap density, and the capture cross section were determined. In addition, it was possible to identify the carrier type (minority and majority) traps in these semiconductors. The results were compared with those obtained in similar materials by other techniques such as conventional DLTS, thermally stimulated currents (TSC), impedance measurements. Q-DLTS appears to be a powerful tool for studying defects in organic semiconductors.