Details

Project TitleNew Hole Transport Layer Materials for Polymer Light Emitting Diodes
Track Code2003-071
Short Description

Northwestern University researchers invented a new hole transport system for polymer light emitting diodes (PLEDs) with negligible visible light absorption, stability to ITO, solvent resistance and tunable electronic properties.

#devices #fabrication #displays

Abstract
ADVANTAGE

Superior PLED performance and efficiency is observed versus conventional PEDOT-PSS based hole transport layer (HTL) devices. ITO interface stability promises enhanced device life and solvent resistance accommodates emissive layer (EML) coating.

SUMMARY

Polymer light emitting diodes are of increasing interest in a wide range of display applications. However conventional hole transport layer poly(3,4-ethylenedioxythiophene)-poly(stryenesulfonate) (PEDOT-PSS) devices exhibit significant visible light absorption and ITO interface instability.

A new crosslinkable siloxane-derivatized hole-transport material (TPD-Si2) in combination with hole transporting or insulating polymers such as poly(9,9-dioctyl-fluorene-co-N-(4- butylphenyl)diphenylamine) (TFB) or polystyrene overcome the above limitations. Spin coating a TPD-Si2 / TFB blend on ITO with thermal curing affords a strongly adherent crosslinked network, providing an efficient HTL stable to subsequent solvent coating operations. The system exhibits ITO interface stability and minimal visible light absorption. PLED devices constructed with ITO/TPD-Si2-TFB blend or PEDOT-PSS/ EML/Ca/Al demonstrate approximately 180% greater maximum light out for the TPD-Si2 /TFB system at comparable turn on voltage (Figure 1). A 40% higher maximum quantum efficiency was also observed compared to the corresponding PEDOT based device (Figure 2), and a current efficiency of 17 cd/A was achieved. Xylene solvent treatment of the cured TPD-Si2/TFB layer had no impact on coating stability.

The electronic (HOMO) properties of the system can be tuned by blending different hole transporting polymers with TPD-Si2 to match the electronic properties of the emissive layer polymer. These advances promise significant improvement in PLED fabrication and performance.

U.S. Patent 7,449,509

 
TagsDEVICES: fabrication, DEVICE: displays
 
Posted DateMay 3, 2011 1:29 PM

Inventor(s)

Qinglan Huang

He Yan

Tobin J. Marks*

Advantages

Superior PLED performance and efficiency is observed versus conventional PEDOT-PSS based hole transport layer (HTL) devices. ITO interface stability promises enhanced device life and solvent resistance accommodates emissive layer (EML) coating.

Status

U.S. Patent 7,449,509 and 8,057,908

Contact Information

Zach Brown, PhD

Invention Associate
(p) 847-491-4629
(e) Zachary.Brown@northwestern.edu