Optimization of yellow phosphorescent organic light-emitting devices based on triplet exciton diffus

Abstract Study on the diffusion of triplet excitons from light emitting layer (EML) in organic light-emitting devices doped with yellow phosphorescent material to the adjacent hole transporting layer (HTL) is carried out, in which a non-doped red phosphorescent ultra-thin layer as an exciton-sensing layer is set in various position of HTL. A diffusion length of triplet exciton between 3 nm and 5 nm is inferred from the observed and disappeared red light emission in electroluminescent spectra. For further device optimization, either 5 nm 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA) or 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as a exciton blocking layer is introduced to block the exciton diffusion. The maximum current efficiency and power efficiency of the optimized device are reached to 24.6 cd/A and 16.3 lm/W, respectively. The high performance is ascribed to confined diffusion of triplet excitons from light-emitting zone and higher radiation efficiency of the triplet exciton.

[1]  S. Tokito,et al.  Highly Efficient and Low‐Voltage Phosphorescent Organic Light‐Emitting Diodes Using an Iridium Complex as the Host Material , 2007 .

[2]  Meng‐Ting Lee,et al.  Host-free, yellow phosphorescent material in white organic light-emitting diodes , 2010 .

[3]  Hartmut Yersin,et al.  Triplet emitters for OLED applications. Mechanisms of exciton trapping and control of emission properties , 2004 .

[4]  Stephen R. Forrest,et al.  Controlling Exciton Diffusion in Multilayer White Phosphorescent Organic Light Emitting Devices , 2002 .

[5]  L. Feldman,et al.  Observation of long-range exciton diffusion in highly ordered organic semiconductors. , 2010, Nature materials.

[6]  High Efficiency Blue Organic LEDs Achieved By an Integrated Fluorescence–Interlayer–Phosphorescence Emission Architecture , 2010 .

[7]  Stephen R. Forrest,et al.  Management of singlet and triplet excitons for efficient white organic light-emitting devices , 2006, Nature.

[8]  Zhenan Bao,et al.  Aryl-Perfluoroaryl Substituted Tetracene: Induction of Face-to-Face pi-pi Stacking and Enhancement of Charge Carrier Properties , 2011 .

[9]  Chen-Ming Chen,et al.  Manufacture of brightness enhancement films (BEFs) by ultraviolet (UV) irradiation and their applications for organic light emitting diodes (OLEDs) , 2010 .

[10]  Ma Dong-ge,et al.  Comparative Study on Hole Transport in N, N′-bis(naphthalen-1-yl)-N,N′-bis(pheny) Benzidine and 4, 4′, 4"-tri(N-carbazolyl)triphenylamine , 2010 .

[11]  Naturally formed graded junction for organic light-emitting diodes , 2003 .

[12]  Dong-Seok Leem,et al.  Estimation of the mean emission zone in phosphorescent organic light-emitting diodes with a thin emitting layer. , 2010, Optics express.

[13]  J. D. Shore,et al.  Highly efficient fluorescent-phosphorescent triplet-harvesting hybrid organic light-emitting diodes , 2010 .

[14]  S. Forrest,et al.  Exciton diffusion lengths of organic semiconductor thin films measured by spectrally resolved photoluminescence quenching , 2009 .

[15]  Hany Aziz,et al.  Probing triplet-triplet annihilation zone and determining triplet exciton diffusion length by using delayed electroluminescence , 2010 .

[16]  B. Ju,et al.  Balancing the white emission of OLED by a design of fluorescent blue and phosphorescent green/red emitting layer structures , 2009 .

[17]  Peter I. Djurovich,et al.  Study of Energy Transfer and Triplet Exciton Diffusion in Hole‐Transporting Host Materials , 2009 .

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

[19]  K. Walzer,et al.  Measuring carrier mobility in conventional multilayer organic light emitting devices by delayed exciton generation , 2008 .

[20]  R. Holmes,et al.  Enhanced exciton diffusion in an organic photovoltaic cell by energy transfer using a phosphorescent sensitizer , 2009 .

[21]  Junsheng Yu,et al.  High efficiency organic light-emitting diodes with yellow phosphorescent emission based on a novel iridium complex , 2007 .

[22]  Stephen R. Forrest,et al.  White Organic Light‐Emitting Devices for Solid‐State Lighting , 2004 .

[23]  H. Naito,et al.  Charge-carrier transport and triplet exciton diffusion in a blue electrophosphorescent emitting layer , 2005 .

[24]  I. McCulloch.  Organic Electronics — From Materials to Applications , 2010, Advanced materials.

[25]  Byung Doo Chin,et al.  Effective hole transport layer structure for top-emitting organic light emitting devices based on laser transfer patterning , 2007 .

[26]  T. George,et al.  Bipolarons in Organic Electroluminescence , 2010 .

[27]  Shigeki Naka,et al.  Nondoped-type white organic electroluminescent devices utilizing complementary color and exciton diffusion , 2002 .

[28]  Jianhua Lu,et al.  White organic light-emitting devices with a bipolar transport layer between blue fluorescent and yellow phosphor-sensitized-fluorescent emitting layers , 2010 .

[29]  Yu Junsheng,et al.  Nondoped Electrophosphorescent Organic Light-Emitting Diodes Based on Platinum Complexes , 2009 .

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

[31]  Zhuozhi Wang,et al.  Highly simplified phosphorescent organic light emitting diode with >20% external quantum efficiency at >10,000 cd/m2 , 2011 .

[32]  High-efficiency red, green and blue phosphorescent homojunction organic light-emitting diodes based on bipolar host materials , 2011 .

[33]  Lixin Xiao,et al.  Nearly 100% Internal Quantum Efficiency in an Organic Blue‐Light Electrophosphorescent Device Using a Weak Electron Transporting Material with a Wide Energy Gap , 2009 .

[34]  Diffusion of triplet excitons in an operational organic light-emitting diode , 2009, 0902.3188.

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