Effect of thickness variation of hole injection and hole blocking layers on the performance of fluorescent green organic light emitting diodes

In this paper we present the effect of thickness variation of hole injection and hole blocking layers on the performance of fluorescent green organic light emitting diodes (OLEDs). A number of OLED devices have been fabricated with combinations of hole injecting and hole blocking layers of varying thicknesses. Even though hole blocking and hole injection layers have opposite functions, yet there is a particular combination of their thicknesses when they function in conjunction and luminous efficiency and power efficiency are maximized. The optimum thickness of CuPc (Copper(II) phthalocyanine) layer, used as hole injection layer and BCP (2,9 dimethyl-4,7-diphenyl-1,10-phenanthroline) used as hole blocking layer were found to be 18 nm and 10 nm respectively. It is with this delicate adjustment of thicknesses, charge balancing is achieved and luminous efficiency and power efficiency were optimized. The maximum luminous efficiency of 3.82 cd/A at a current density of 24.45 mA/cm(2) and maximum power efficiency of 2.61 lm/W at a current density of 5.3 mA/cm(2) were achieved. We obtained luminance of 5993 cd/m(2) when current density was 140 mA/cm(2). The EL spectra was obtained for the LEDs and found that it has a peaking at 524 nm of wavelength. (C) 2012 Elsevier B.V. All rights reserved.

[1]  Shin-ichiro Tamura,et al.  A Blue Organic Light Emitting Diode , 1999 .

[2]  A. Jen,et al.  High-efficiency light-emitting diodes using neutral surfactants and aluminum cathode , 2005 .

[3]  IEEE Spectrum , 2022 .

[4]  M. Stössel,et al.  Mechanisms of injection enhancement in organic light-emitting diodes through an Al/LiF electrode , 2001 .

[5]  Wen-Jhy Lee,et al.  Dramatic improving luminous efficiency of organic light emitting diodes under low driving current using nitrogen doped hole transporter , 2003 .

[6]  M. Tsuchida,et al.  Organic EL cells using alkaline metal compounds as electron injection materials , 1997 .

[7]  S. Forrest,et al.  Nearly 100% internal phosphorescence efficiency in an organic light emitting device , 2001 .

[8]  Hany Aziz,et al.  CuPc buffer layer role in OLED performance: a study of the interfacial band energies , 2004 .

[9]  T. Tsutsui,et al.  Carrier transport properties of organic materials for EL device operation , 2000 .

[10]  Sung-Yoon Huh,et al.  Inverted top-emitting organic light-emitting diodes by whole device transfer , 2008 .

[11]  X. D. Gao,et al.  Interfacial reactions at Al/LiF and LiF/Al , 2009 .

[12]  M. Ferenets,et al.  Thin Solid Films , 2010 .

[13]  Ying Zheng,et al.  Effects of triplet energies and transporting properties of carrier transporting materials on blue phosphorescent organic light emitting devices , 2008 .

[14]  C. Tang,et al.  Enhanced electron injection in organic electroluminescence devices using an Al/LiF electrode , 1997 .

[15]  Tatsuo Mori,et al.  A discussion of conduction in organic light-emitting diodes , 2003 .

[16]  Shuyan Song,et al.  High-Brightness, Broad-Spectrum White Organic Electroluminescent Device Obtained by Designing Light-Emitting Layers as also Carrier Transport Layers , 2010 .

[17]  Stephen R. Forrest,et al.  Improved energy transfer in electrophosphorescent devices , 1999 .

[18]  Zheng-Hong Lu,et al.  Unlocking the full potential of organic light-emitting diodes on flexible plastic , 2011 .

[19]  N. Liu,et al.  The enhanced electron injection by fluorinated tris-(8-hydroxy-quinolinato) aluminum derivatives in high efficient Si-anode OLEDs , 2011 .

[20]  Horst Vestweber,et al.  Highly efficient and stable organic light-emitting diodes , 1997 .

[21]  W. R. Salaneck,et al.  Interfacial chemistry of Alq3 and LiF with reactive metals , 2001 .

[22]  Stephen R. Forrest,et al.  The dawn of organic electronics , 2000 .

[23]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[24]  George G. Malliaras,et al.  The roles of injection and mobility in organic light emitting diodes , 1998 .

[25]  Yan Jiang,et al.  Electroluminescence of blends of hole-transporting polymer and hole-blocking polymer , 2006 .

[26]  C. Tang,et al.  Organic Electroluminescent Diodes , 1987 .

[27]  Stephen R. Forrest,et al.  Architectures for efficient electrophosphorescent organic light-emitting devices , 2002 .

[28]  W. R. Salaneck,et al.  Electroluminescence in conjugated polymers , 1999, Nature.

[29]  Chih-I Wu,et al.  Energy structures and chemical reactions at the Al∕LiF∕Alq3 interfaces studied by synchrotron-radiation photoemission spectroscopy , 2005 .

[30]  Liduo Wang,et al.  A microfluidic device using a green organic light emitting diode as an integrated excitation source. , 2005, Lab on a chip.

[31]  Charles E. Swenberg,et al.  Electronic Processes in Organic Crystals and Polymers , 1999 .

[32]  R. Rosenfeld.  Nature , 2009, Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery.

[33]  Chun‐Sing Lee,et al.  High-efficiency polymer electrophosphorescent diodes based on an Ir (III) complex , 2005 .

[34]  Zhenan Bao,et al.  Organic field‐effect transistors with high mobility based on copper phthalocyanine , 1996 .

[35]  Li Jinmin,et al.  Organic light emitting diodes with an organic acceptor/donor interface involved in hole injection , 2007 .

[36]  K. Leo.  Organic light-emitting diodes: Efficient and flexible solution , 2011 .

[37]  Stephen R. Forrest,et al.  Measuring the Efficiency of Organic Light‐Emitting Devices , 2003 .

[38]  Andrew G. Glen,et al.  APPL , 2001 .

[39]  Chih-Hung Hsiao,et al.  Emitting layer thickness dependence of color stability in phosphorescent organic light-emitting devices , 2010 .

[40]  W. A. Gambling,et al.  Electron drift mobility and electroluminescent efficiency of tris(8-hydroxyquinolinolato) aluminum , 1999 .

[41]  Jan Birnstock,et al.  High-efficiency and low-voltage p‐i‐n electrophosphorescent organic light-emitting diodes with double-emission layers , 2004 .

[42]  Shizuo Tokito,et al.  Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer , 2001 .

[43]  Yongsheng Wang,et al.  Improved performance of organic light-emitting diodes with cesium chloride inside tris (8-hydroxyquinoline) aluminum , 2011 .

[44]  Paul Seidler,et al.  Organic–inorganic multilayer structures: a novel route to highly efficient organic light-emitting diodes , 1999 .

[45]  The depth profile of core energy levels: Electronic structure of buried organic/metal interfaces examined by X-ray photoemission and target factor analysis , 2011 .

[46]  Lei Wang,et al.  26th Annual International Conference of the IEEE EMBS , 2004 .

[47]  J. Andre,et al.  Characterization of metallophthalocyanine‐metal contacts: Electrical properties in a large frequency range , 1984 .

[48]  Y. Masumoto,et al.  Application of organic bathocuproine-based alloy film to organic light-emitting diodes , 2008 .

[49]  Nigel P. Beard,et al.  Thin-film polymer light emitting diodes as integrated excitation sources for microscale capillary electrophoresis. , 2004, Lab on a chip.

[50]  Dieter Neher,et al.  Polymer electrophosphorescence devices with high power conversion efficiencies , 2004 .

[51]  Stephen R. Forrest,et al.  EXCITONIC SINGLET-TRIPLET RATIO IN A SEMICONDUCTING ORGANIC THIN FILM , 1999 .

[52]  S. Forrest,et al.  VERY HIGH-EFFICIENCY GREEN ORGANIC LIGHT-EMITTING DEVICES BASED ON ELECTROPHOSPHORESCENCE , 1999 .

[53]  Lihua Zhu,et al.  Influences of hole blocking bathocuproine layer on emission of organic light emitting devices , 2003 .