• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.158-161
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• 2004

We have studied a lifetime in organic light-emitting diodes depending on buffer layer. A transparent electrode of indium-tin-oxide(ITO) was used as an anode. And the cathode for electron injection was LiAl. Phthalocyanine Copper(CuPc), Poly(3,4-ethylenedioxythiophene):poly (PEDOT:PSS), or poly (9-vinylcarbazole)(PVK) material was used as a buffer layer. A thermal evaporation was performed to make a thickness of 40nm of TPD layer at a rate of $0.5{\sim}1\;{\AA}/s$ at a base pressure of $5{\times}10^{-6}\;torr$. A material of tris(8-hydroxyquinolinate) Aluminum($Alq_3$) was used as an electron transport and emissive layer. A thermal evaporation of $Alq_3$ was done at a deposition rate of $0.7{\sim}0.8[{\AA}/s]$ at a base pressure of $5{\times}10^{-6}\;torr$. By varying the buffer material, hole injection at the interface could be controlled because of the change in work function. Devices with CuPc and PEDOT:PSS buffer layer are superior to the other PVK buffer layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.11
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• pp.980-986
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• 2009

In a triple-layered structure of ITO/N,N'-diph enyl-N,N'bis(3-methylphenyl)-1,1' - biphenyl-4,4'-diamine(TPD)/tris(8-hydroxyquinoline)aluminum($Alq_3$)/(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline(BCP)/Al device, we have studied the electrical and optical characteristics of organic light-emitting diodes(OLEDs) depending on the deposition condition of BCP layer. Several different sizes of holes on boat and several different deposition rates were employed in evaporating the organic materials. And then, electrical properties of the organic light-emitting diodes were measured and the performance of the devices was analyzed. It was found that the hole-size of crucible boat and the evaporation rate affect on the surface roughness of BCP layer as well as the performance of the device. When the hole-size of crucible boat and the deposition rate of BCP are 1.2 mm and $1.0\;{\AA}/s$, respectively, average surface roughness of BCP layer is lower and the efficiency of the device is higher than the ones made with other conditions. From the analysis of current density-luminance-voltage characteristics of a triple layered device, we divided the conductive mechanism by four region according to applied voltage. So we have obtained a coefficient of ${\beta}_{ST}$ in schottky region is $3.85{\times}10^{-24}$, a coefficient of ${\beta}_{PF}$ in Poole-Frenkel region is $7.35{\times}10^{-24}$, and a potential barrier of ${\phi}_{FN}$ in Fower-Nordheim region is 0.39 eV.