Graphene/TiO2 electrodes boost flexible OLEDs’ efficiency
Removing the need for ITO as a transparent electrode on displays is on the agenda of many OEMs, not only because the thin oxide layer is brittle and prone to cracking upon flexure, but also because of supply and pricing fluctuations.
The new composite structure stacks a high refractive index (nH) TiO2 layer with low-index (nL) hole-injection layers sandwiching graphene electrodes, which the researchers say, results in an ideal situation where the synergetic collaboration of the high- and low-index layers enables optical management of both resonance effect and Surface Plasmon Polariton (SPP) loss to the advantage of maximal out-coupling.
In their experiments, the team of researchers from the School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) and from the Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) obtained OLEDs exhibiting ultrahigh External Quantum Efficiency (EQE) of 40.8 and 62.1% (64.7 and 103% with a half-ball lens) for single- and multi-junction devices, respectively. They reported a power efficiency 160.3lm/W, beating all previous attempts using graphene as a transparent electrodes.
What’s more, thanks to the TiO2 layers, the OLEDs made on plastics with those electrodes were repeatedly bendable at a radius of only 2.3mm (1,000 bending cycles). They explained this high operational flexibility by the crack-deflection toughening of the TiO2 layer, withstanding flexural strain up to 4%.
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
