Approaching ultimate flexible organic light-emitting diodes using a graphene anode

Abstract

Ultimate flexible organic light-emitting diodes (OLEDs) should have an ultra-high device efficiency, a low-efficiency roll-off at a high luminance and excellent flexibility. Here, we realized flexible tandem OLEDs using a graphene anode with a very high electroluminescent efficiency of~205.9 cd A − 1 , 45.2% (~396.4 cd A − 1 , 87.3% with a hemispherical lens) and a very low efficiency roll-off at a high luminance of~6.6% at 10 000 cd m − 2 (~3.8% with a hemispherical lens) by stacking two organic electroluminescence (EL) units. For the first time, we used an easily controlled and low-temperature processable charge generation layer with lithium nitride (Li 3 N). This simultaneously provided efficient stacking of EL units and enhanced compatibility of the flexible device on a thin plastic substrate. The flexible tandem OLEDs with a graphene anode also showed great flexibility against bending up to a bending strain of 6.7%. These results represent a significant advancement towards the production of next-generation flexible displays and solid-state lighting that use a graphene anode.

Work Function Tunability of Graphene with Thermally Evaporated Rhenium Heptoxide for Transparent Electrode Applications

“…Graphene, a monolayer thick allotrope of carbon, is a 2D material, which shows mechanical flexibility and very high mobility of charge carriers complemented by unusual optical transparency in the range of visible light . It is believed that graphene can serve as a conducting transparent electrode in organic light‐emitting diodes (OLEDs) and organic photovoltaics (OPVs) due to its low resistance below 50 Ω □ −1 and optical transmittance of at least 90%. Unfortunately, graphene in its pure form does not meet all the requirements for such applications.…”

“…This is because of the graphene work function which is in the range of 4.2–4.5 eV . As a result, graphene work function does not satisfy the requirements of the energy‐level alignment when embedded in OLEDs/OPVs . Nevertheless, the desired functionality of graphene in a wide range of fields is gained when graphene is combined with another class of materials, resulting in the formation of composite materials with improved properties .…”

Flexible Near‐Infrared Plastic Phototransistors with Conjugated Polymer Gate‐Sensing Layers

“…Compared to inorganic materials, organic materials are relatively soft and lightweight so that organic electronic devices can be flexible and bendable as proven by organic light‐emitting devices (OLEDs) for display applications . In this regard, organic materials have been tried for the fabrication of NIR detectors with a device geometry of diode or transistor.…”

Interfacial engineering of graphene for highly efficient blue and white organic light-emitting devices

“…The ultimate challenge in developing highly efficient OLEDs with graphene electrodes is universally considered to reduce sheet resistance and tune work function of graphene so as to realize a fine control over the carrier injection and transport 1 – 3 . Usually, both low sheet resistances and high work functions of graphene were achieved via chemical doping with various acids 1 , 4 – 6 , metal halides 7 – 13 , metal oxides 14 – 16 and other organic molecules (e.g., bis(trifluoromethanesulfonyl)amide 2 or triethyloxonium hexachloroantimonate 17 ). With these chemical treatments, high luminous efficiencies of both green and white emissions over 250 cd A −1 (>160 lm W −1 ) and 120 cd A −1 (~90 lm W −1 ) were achieved in graphene-based OLEDs 17 , which are superior to device performances using ITO 18 , carbon nanotubes 19 , 20 , metal nanowires 21 , metal grid 22 and other conductive polymer 23 anodes.…”