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Whitcher T.J.,University of Malaya | Yeoh K.H.,University of Malaya | Yeoh K.H.,ItraMAS Corporation. Sdn. Bhd. | Chua C.L.,University of Malaya | And 5 more authors.
Current Applied Physics | Year: 2014

The work function of indium tin oxide (ITO) was increased by treating ITO with dichlorobenzene with UV light. Carbon contamination of the Cl-ITO was measured using X-ray Photoelectron Spectroscopy (XPS) and argon ion sputtering was used to remove the carbon from the surface. It was found that the carbon contamination from residual dichlorobenzene significantly lowered the work function of the ITO and after argon ion sputtering the work function increased to 5.8 eV. It was found that chlorination of ITO occurs after more than 6 min of UV exposure. Further sputtering of ITO resulted in the removal of the functionalized chlorine, the introduction of argon ion contaminants on the ITO decreases its work function. © 2014 Elsevier B.V. All rights reserved. Source

Yeoh K.H.,University of Malaya | Yeoh K.H.,ItraMAS Corporation. Sdn. Bhd. | Chua C.L.,University of Malaya | Woon K.L.,University of Malaya
Synthetic Metals | Year: 2013

The effects of triplet energy shielding and nanoscale surface modification using Triton X-100 in a single layer solution processed blue phosphorescent organic light emitting diodes (PhOLED) was investigated. It was found that with 3.2 wt% Triton X-100 doping, the power efficiency of the device doubled at brightness of 1000 cd/m2. The insertion Triton X-100 provides separation between guest-host which reduced back energy transfer from the high triplet of FIrpic (2.7 eV) to the low triplet of PVK host (2.5 eV). Atomic force microscopy (AFM) indicates that phase separation of Triton X-100 modified the emissive layer (EML) surface morphology. This surface modification roughened the film surface at the EML/cathode interface. These combined effects improves the performance of the solution processed blue PhOLED. © 2013 Elsevier B.V. All rights reserved. Source

Talik N.A.,University of Malaya | Talik N.A.,ItraMAS Corporation. Sdn. Bhd. | Yeoh K.H.,University of Malaya | Yeoh K.H.,ItraMAS Corporation. Sdn. Bhd. | And 4 more authors.
Journal of Luminescence | Year: 2014

A novel solution processable charge generating layer (CGL) that consists of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN6)/Poly(N- vinylcarbazole) (PVK): 1,1-bis-(4-bis(4-tolyl)-aminophenyl) cyclohexene (TAPC) for a tandem green phosphorescent organic light emitting diode (PHOLED) is demonstrated. The use of orthogonal solvent to dissolve HATCN6 and PVK:TAPC is the key to overcome the interface erosion problem for the solution processed CGL. The current efficiency of the 2 wt% TAPC mixed with PVK is the highest at 24.2 cd/A, which is more than three-folds higher than that of the single device at 1000 cd/m2. © 2014 Elsevier B.V. Source

Whitcher T.J.,University of Malaya | Yeoh K.H.,University of Malaya | Yeoh K.H.,ItraMAS Corporation. Sdn. Bhd. | Ng Y.B.C.,University of Malaya | And 11 more authors.
Journal of Physics D: Applied Physics | Year: 2013

The work function of indium tin oxide (ITO) was modified using caesium fluoride (CsF). Various concentrations of CsF was spin-coated on top of ITO and baked while the residual CsF was washed away with DI water. The work function of all the ITO samples was measured using ultraviolet photoelectron spectroscopy and it was found that the work function of ITO reaches as high as 5.75 eV. The work function rapidly increases with small concentrations of CsF solution and then decreases for higher concentrations. Using atomic force microscopy and x-ray photoelectron spectroscopy, the cause was determined to be the change in surface roughness and the oxygen concentration, with the former having a much greater influence on the work function than the latter. The current density of ITO/poly(vinylcarbazole)/Al hole-only devices using the modified ITO increases by more than seven orders of magnitude compared with the control device. © 2013 IOP Publishing Ltd. Source

Woon K.L.,University of Malaya | Woon K.L.,National Tsing Hua University | Hasan Z.A.,University of Malaya | Hasan Z.A.,ItraMAS Corporation. Sdn. Bhd. | And 6 more authors.
RSC Advances | Year: 2015

Intermolecular interactions among π conjugated semiconducting molecules often give rise to totally different optical behaviours between the solid state and dilute phases. Phosphorescence spectra observed in the solid state are often lowered compared with dilute forms resulting in the red-shift of the phosphorescence spectra. Here, we demonstrate that this red-shift can be reduced by introducing side groups. We also show that such a shift is a function of interchromophoric distance with fast exponential decay. Furthermore, we show conclusively that triplet exciton transfer between the hosts and the bis[2-(4F,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(iii) can be described in terms of the Boltzmann factor using triplet energies obtained from the solid state. These results will have implications in molecular design that utilizes triplet excitons such as organic light emitting diodes and singlet fission solar cells. © The Royal Society of Chemistry 2015. Source

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