(4ad) High-Performance Phosphorescent Organic Light-Emitting Diodes (PhOLEDs) Achieved By Orthogonal Solution-Processing Strategy

Phosphorescent organic light-emitting diodes (PhOLEDs) are being extensively explored for scientific interest and for commercial applications in display technology and solid state lighting. High-performance PhOLEDs are currently fabricated by sequential thermal evaporation to obtain multilayered structures. Despite the considerable progress made in developing vacuum-processed PhOLEDs, studies of potentially low cost solution-based high-performance PhOLEDs are relatively few. One of the key challenges to fabricate high performance multilayered organic electronic devices by solution-processing is that the solvent used to deposit the subsequent layer can easily dissolve the underlying layer. A general approach to overcome this problem is to develop an orthogonal solution-processing strategy, whereby a second solvent is used to deposit the overlayer without dissolution of the underlying layers. We have developed a novel orthogonal solution-processing of electron-transport materials (ETMs) and fabrication of high-performance multilayered PhOLEDs with triplet emitter-doped polymeric emission layers followed by orthogonal solution-processing of new or commercial small molecule ETMs. Charge injection and transport of ETMs were enhanced by orthogonal solution-processing and thus led to significant increase of the overall device performance. We have achieved a luminous efficiency of 37.7 cd/A with an EQE of 19.0%, which is the best device performance observed to date in all-solution-processed blue PhOLEDs. We also show that the orthogonal solution-processed electron-transport layer (ETL) exhibits a unique rough surface morphology which facilitates efficient charge-injection and transport from the cathode metal. The orthogonal solution processing demonstrated here is a promising strategy for the fabrication of high performance multilayered PhOLEDs and other organic electronic devices.

Selected Publications:

1. Earmme, T.; Jenekhe S. A. “Solution-Processed, Alkali Metal-Salt-Doped, Electron-Transport Layers for High-Performance Phosphorescent Organic Light-Emitting Diodes,” Adv. Funct. Mater. 2012, 22, 5126-5136.

2. Earmme, T.; Jenekhe, S. A. “High-Performance Multilayered Phosphorescent OLEDs by Solution-Processed Commercial Electron-Transport Materials,” J. Mater. Chem. 2012, 22, 4660-4668. (Selected as Hot Paper by Editor)

3. Ahmed, E.; Earmme, T.; Jenekhe, S. A. “New Solution-Processable Electron Transport Materials for Highly Efficient Blue Phosphorescent OLEDs,” Adv. Funct. Mater. 2011, 21, 3889-3899.

4. Earmme, T.; Ahmed, E.; Jenekhe, S. A. “Solution-Processed Highly Efficient Blue Phosphorescent Polymer Light-Emitting Diodes Enabled by a New Electron Transport Material,” Adv. Mater. 2010, 22, 4744-4748.

5. Ahmed, E.; Earmme, T.; Ren, G.; Jenekhe, S. A. “Novel n-Type Conjugated Ladder Heteroarenes: Synthesis, Self-Assembly of Nanowires, Electron transport, and Electroluminescence of Bisindenoanthrazolines,” Chem. Mater. 2010, 22, 5786-5796.

6. Earmme, T.; Ahmed, E.; Jenekhe, S. A. “Highly Efficient Phosphorescent Light-Emitting Diodes by Using an Electron-Transport Materials with High Electron Affinity,” J. Phys. Chem. C. 2009, 113, 18448-18450.