Thermal detection of trapped charge carriers in organic transport materials

Norwin von Malm; Juergen Steiger; Torsten Finnberg; Roland Schmechel; Heinz von Seggern

doi:10.1117/12.451903

3 March 2003 Thermal detection of trapped charge carriers in organic transport materials

Norwin von Malm, Juergen Steiger, Torsten Finnberg, Roland Schmechel, Heinz von Seggern

Proceedings Volume 4800, Organic Light-Emitting Materials and Devices VI; (2003) https://doi.org/10.1117/12.451903
Event: International Symposium on Optical Science and Technology, 2002, Seattle, WA, United States

Abstract

The effect of trap states on the transport and luminescence properties of organic light emitting diodes (OLEDs) is studied. For trap level detection energy resolved thermally stimulated current (TSC) measurements known as fractional glow are utilized to determine the density of occupied states (DOOS) in various organic semiconductors such as the small molecule systems Alq₃ [aluminum tris(8-hydroxyquinoline)], 1-NaphDATA {4,4',4"-tris-[N-(1-naphtyl)-N-phenylamino]-triphenylamine} and α-NPD [N,N'-di-(1-naphthyl)-N,N'-diphenylbenzidine] and the polymeric semiconductor MDMO-PPV {poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene]}. Characteristic differences in the trap spectra are obtained and interpreted in terms of possible structural and compositional origins of the investigated materials. In order to judge the formation process of traps and their practical consequences on the charge carrier transport I-V and L-V characteristics of 1-NaphDATA doped α-NPD devices and α-NPD doped 1-NaphDATA devices were compared to respective non-doped samples. A clearly reduced current and luminescence was found only in the former case. It was possible to conclude that the detected electronic trap states either act as hole traps or as scattering centers. Furthermore, pulsed transport studies on ITO/α-NPD/Alq₃/Al devices show thte critical influence of traps on the dynamical performance of the charge transport. In a two-pulse experiment the carrier injection and trap depletion can be separated.

Citation Download Citation

Norwin von Malm, Juergen Steiger, Torsten Finnberg, Roland Schmechel, and Heinz von Seggern "Thermal detection of trapped charge carriers in organic transport materials", Proc. SPIE 4800, Organic Light-Emitting Materials and Devices VI, (3 March 2003); https://doi.org/10.1117/12.451903

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