High-efficiency, solution-processed, multilayer phosphorescent organic light-emitting diodes with a copper thiocyanate hole-injection/hole-transport layer.

Ajay Perumal,Martyn A Mclachlan,Shrawan Jha,Hendrik Faber,Pichaya Pattanasattayavong,Claire Burgess,Thomas D Anthopoulos,Nir Yaacobi‐Gross,Paul N Stavrinou,Donal D C Bradley

doi:10.1002/adma.201403914

Ajay Perumal, Martyn A Mclachlan + Show 8 more

Open Access

https://doi.org/10.1002/adma.201403914

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Abstract

Copper thiocyanate (CuSCN) is introduced as a hole-injection/hole-transport layer (HIL/HTL) for solution-processed organic light-emitting diodes (OLEDs). The OLED devices reported here with CuSCN as HIL/HTL perform significantly better than equivalent devices fabricated with a PEDOT:PSS HIL/HTL, and solution-processed, phosphorescent, small-molecule, green OLEDs with maximum luminance ≥10 000 cd m(-2) , maximum luminous efficiency ≤50 cd A(-1) , and maximum luminous power efficiency ≤55 lm W(-1) are demonstrated.

Highlights

Following early breakthrough reports on vacuum-deposited small molecule and solution-processed conjugated polymer organic light-emitting diodes (OLEDs),[1] tremendous progress has been made in commercializing smartphone, tablet, and television display products
In the PEDOT:PSS system, PSS chains template the oxidative polymerization of ethylenedioxythiophene (EDOT) and are retained as a counter-ion scaffold that the doped PEDOT decorates and that promotes solubility and stability.[7a,b] PEDOT:PSS does, have several limitations, that its acidity can damage indium tin oxide (ITO) anodes and emission layer (EML) materials, its work function is rather low, it is not very effective as an electron-blocking layer, and it does not have high thermal stability, especially in air.[7c,d] Insertion of arylamine polymer based thin film interlayers helps to address some of these issues[8] but unfavorably adds two process steps to device fabrication
An alternative approach is to use an inorganic metal oxide hole-injection/hole-transport layer (HIL/HTL) such as tungsten oxide (WO3), molybdenum oxide (MoO3), or nickel oxide (NiO).[4i,9] These are traditionally deposited via thermal evaporation under high vacuum[10] but solution-processed metal oxide layers are being explored, based on thermal decomposition of organic–inorganic hybrid precursors or on the deposition and annealing of suspensions of nanoparticles sheathed in organic solubilizing/stabilizing layers.[11]

Summary

Introduction

Following early breakthrough reports on vacuum-deposited small molecule and solution-processed conjugated polymer organic light-emitting diodes (OLEDs),[1] tremendous progress has been made in commercializing smartphone, tablet, and television display products. They can have a significant effect on short-circuit current density.[15] Diffuse reflectance measurements (Figure S3, Supporting Information) show that spin-coated CuSCN films are significantly scattering www.advmat.de www.MaterialsViews.com extraction[24] and organic photovoltaic (OPV) light trapping,[25] resulting in higher efficiencies; it supports stimulated emission.[26] Again, it will be of interest to systematically adjust deposition conditions to control this effect.

Results

Conclusion