Organic Light-Emitting Diodes and Methods for Assembly and Enhanced Charge Injection (22012)
The integrity of electrode/organic interfacial contact is crucial to the performance and stability of organic light-emitting diodes (OLEDs). This invention addresses the problem by employing a well defined self-assembly strategy that improves the ITO anode / hole transport layer (HTL) interface morphology and integrity, hence device performance and thermal robustness. These self-assembling interlayer materials may be readily applied to enhanced performance and stability in OLEDs, organic FETs, and other electronic and photonic devices.
ADVANTAGE: New self-assembling interlayer materials that enhance OLED performance and stability have been created. The materials are spin-coatable and applicable to a range of ITO/organic devices.
SUMMARY: OLEDs have great potential in a wide range of display applications. Efforts to improve OLED performance include understanding the fundamentals of charge injection efficiency at the electrode/organic interface, crucial to function and device stability. A variety of nanoscale structures have been interposed at the anode/hole-transport layer (HTL) and cathode/electron-transport layer (ETL) interfaces to improve OLED performance. However, physical decohesion at the hydrophobic arylamine HTL- hydrophilic oxide anode interface has been generally overlooked. For ITO/TPD/Alq(tris(quinoxalinato)Al(III))/Al - type devices, any process disrupting HTL continuity will risk device degradation. This invention employs a self-assembly strategy to improve ITO/HTL interface morphology, integrity, that enhance device performance and stability.
Adhesion promoting, crosslinkable arylamine analogs (TPDa) of the archetypical HTL component TPD have been created. The amines can be readily spin coated and thermally cured on anode and device surfaces. Significant improvement in OLED thermal stability and performance are observed. Thus a 40 nm TPDa coated cured film exhibits only 5 wt% weight loss at 400ºC. Furthermore, cyclic voltammetry of a similarly coated ITO electrode reveals a pin hole free film with excellent hole transport and electrochemical stability. Thermal cycling at 80ºC of ITO/TPDa/TPD interfaces show no evidence of film dewetting or decohesion in contrast to a bare ITO/TPD interface.
ITO/interlayer/TPD/Alq/Al devices prepared with the TPDa amine interlayer exhibit greater maximum light output (up to ~90,000 cd/m2), external quantum efficiency (~5%; ~18 lumens/W) and lower turn-on voltage than devices without TPDa. Equally important, the devices are far more stable to thermal cycling.
Qinglan Huang, Ji Cui, Jon G.C. Veinot, Tobin J. Marks
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