OLED

(version française)

Nanostructures, Nanocomposites

ORGANIC LIGHT EMITTING DIODES (OLEDs)

Person in charge :

Thien-Phap NGUYEN (PR)

Participants:

Philippe LE RENDU (thèse) Mohammed ZEMMOURI (thèse)

Cédric RENAUD (thèse) Hassina DERBAL (thèse)

Chih WEN LEE (thèse) Yves JOSSE (Stagiaire M2)

Summary:

Objectives
Results
Collaborations, contrats
PhD theses
Publications

Objectives

Organic light emitting diodes (OLEDs) appear today to be one of the most promising applications for conjugated polymers. Using polymers or other organic materials as the active layer within LEDs allows us to obtain specific properties which are inaccessible to conventional inorganic LEDs: low mass, flexibility, large active surface, and high luminosity.

We produce light emitting diodes using polymers and various organic materials, and study the different physio-chemical phenomena which arise during the operation of the LEDs: we characterise the active materials, the conduction mechanisms in the samples, the role of interfaces for charge injection, the structure of these interfaces, and degradation phenomena. Based on the knowledge and understanding gained during these studies, we propose new strategies and approaches to improve diode performance, and apply this when studying new materials and structures. Better understanding of diode operation is obtained through appropriate characterisation techniques (trapping, electrical transport, degradation). At the same time, improvements in device performance can be achieved. Meanwhile we use the results of characterisation and electrical analysis of organic semiconductors in order to model the processes of conduction and transport in the materials studied.

Results

We have shown that the use of films of indium tin oxide (ITO) as the anode in devices can pose stability problems due to decomposition of the oxide in contact with the polymer films.

A reaction between the materials forms complexes at the interface, which facilitates the diffusion of metal atoms in the active film, which in turn, leads to deterioration in the transport and emission properties of the sample.

DLTS measurements

DLTS spectra of MEH-PPV

We have also shown that the inverse structure (emission from the top electrode) leads to the same phenomena and inconveniences as the conventional structures.

In many various organic samples, the identification of defects using thermally stimulated current (TSC) and charge based deep level transient spectroscopy (Q-DLTS) has allowed us to determine the energetic band diagrams for the structures, with detailed parameterised data of the gap states. However these techniques provide no information on the nature of these defects, and for this identification we are currently preparing other experiments.

Electroluminescent diode containing derived from polycetylene

Collaborations, contracts

Europe OLLA Integrated Contract 2004-2008
Toulouse, Strasbourg: ANR Contract 2005-2008
Taipei (Taiwan): CNRS/NST Contract 2004-2006
Other cooperations : Angers, Le Mans, Madrid (Espagne), Chiao Tung (Taiwan), Sydney(Australie), Hanoï (Vietnam).

Thèses

Joseph Ip – Juillet 2004 -Creation and study of diodes produced from a derivative of PPV: 4,4'-bis(4-dimethylaminostryrl) benzene (DMASB). Influence of hard interfaces on the electrical characteristics and transport phenomena.

Sheng Hsiung YANG – Août 2004 - Synthesis and study of composites (polymer-inorganic material) used as active elements in electroluminescent diodes.

Lotfi DJEBARRA – mars 2006 -Concept, production and study of polymer-oxide composites integrable into the production of high performance condensators.

Chun Hao HUANG – Juin 2006 - Synthesis and study of the electro-optical properties of polyacetylene disubstitutes.

Publications

1. Study of the interface formed between poly(2-methoxy-5-(2’-ethyl-hexyloxyl)-p-phenylene vinylene) and indium tin oxide in top emission devices.

T. P. NGUYEN, J. IP, C. RENAUD, C. H. HUANG, C. GUILLEN, J. HERRERO

Applied Surface Science, 252, 8388-8393 (2006).

2. Self-Assembly Monolayer of Anatase Titanium Oxide from Solution Process on Indium Tin Oxide Glass Substrate for Polymer Photovoltaic Cells

C. H. HUANG, C. H. HUANG, T. P. NGUYEN, C. H. HSU.

Thin Solid Films , 515, 6493-6496 (2007).

3. Study of traps in polydiacetelene based devices by thermally stimulated current technique.

C. RENAUD, C.H. HUANG, M. ZEMMOURI, P. LE RENDU , T. P. NGUYEN

European Journal of Applied Physics 36 , 215-218 (2007).

4. Defects In OrganicElectronic Devices

T. P. NGUYEN

Physica Status Solidi (a) 205, 162-166 (2008).

5. Investigations of organic light emitting diodes with CdSe(ZnS) quantum dots

C. W. LEE, C. H. CHOU, J. H. HUANG, C H. HSU, T. P. NGUYEN

Materials Science & Engineering B 147 (2008) 307-311.