Multilayered graphene anode for blue phosphorescent organic light emitting diodes

Abstract

In this work, we report on blue organic light emitting devices (OLEDs), which have multilayered graphene as its anode. Our graphene films have been grown catalytically and transferred to the support. The fabricated blue OLEDs with graphene anode showed outstanding external quantum efficiency of 15.6% and power efficiency of 24.1 lm/W at 1000 cd/m2. Weak oxygen plasma treatments on graphene film surfaces improved the injection property between the anode and hole injection layer.

Multifunctional oxides for integrated manufacturing of efficient graphene electrodes for organic electronics

“…In addition, the XPS data confirm the p-doping of graphene upon WO 3 deposition, as seen in the corresponding graphene C1s core level shift of around 0.2 eV towards lower binding energies. In a previous study on MoO 3 doped graphene, a similar shift of 0.25 eV has been observed. 18 For comparison, the Fermi level shift induced by metal oxide doping (WO 3 and MoO 3 ) is significantly larger as reported for conventional HNO 3 doping of graphene ($0.12 eV).…”

“…9,18,19,31 Though we emphasize that our method is highly relevant for a number of other optoelectronic applications using MoO 3 as a p-type dopant for graphene and CNTs. In addition, MoO 3 and WO 3 have been identified as ITO sputtering protection layer in OLEDs and organic solar cells, where a 40-60 nm thick metal oxide layer can effectively prevent the sensitive organic layers from the high kinetic particle bombardment. [34][35][36] We note that thermally evaporated metal oxides, such as MoO 3 and WO 3 , grow as sub-stoichiometric thin film, which make these materials n-type conductive due to oxygen vacancies.…”

“…In addition, MoO 3 and WO 3 have been identified as ITO sputtering protection layer in OLEDs and organic solar cells, where a 40-60 nm thick metal oxide layer can effectively prevent the sensitive organic layers from the high kinetic particle bombardment. [34][35][36] We note that thermally evaporated metal oxides, such as MoO 3 and WO 3 , grow as sub-stoichiometric thin film, which make these materials n-type conductive due to oxygen vacancies. 37 On the other hand, a very strong chemical reduction, e.g., as a result of high evaporation temperatures or adsorbates on the surface, leads to a different metal oxide composition with a high amount of MoO 2 and WO 2 suboxides.…”

“…1,2 The use of graphene as a potential replacement of brittle and increasingly expensive indium tin oxide (ITO) as a transparent conducting electrode (TCE) in organic electronics and optoelectronic applications has attracted a lot of research interest, [3][4][5][6] but effective integration into working devices remains challenging.…”

“…18,19 This is followed by thermal deposition of WO 3 through a shadowmask which induces p-doping of graphene due to charge transfer. 18,19 An O 2 plasma step is then used to etch the regions that are not covered by WO 3 while the covered graphene areas are protected against etching leading to the desired pattern formation (Figure 1(b)). An OLED stack with a perpendicular patterned top electrode is evaporated on top of the WO 3 covered graphene stripes.…”