We report the design, synthesis and characterization, thermal and photophysical properties of two silane based electron transport materials, dibenzo[b,d]thiophen-2-yltriphenylsilane (Si?87) and (dibenzo[b,d]thiophen-2-yl)diphenylsilane (Siφ88) and their performance in blue organic light emitting devices (OLEDs). The utility of these materials in blue OLEDs with iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2’]picolinate (Firpic) as the phosphorescent emitter was demonstrated. Using the silane Siφ87 as the electron transport material (ETm), an EQE of 18.2% was obtained, with a power efficiency of 24.3 lm/W (5.8V at 1 mA/cm 2 ), in a heterostructure. When Siφ88 is used, the EQE is 18.5% with a power efficiency of 26.0 lm/W (5.5V at 1 mA/cm 2 ).
KeywordsElectron TransportOLEDTriplet Energy
Blochwitz, M. Pfeiffer, M. Hofmann and K. Leo, “Non-Polymeric OLEDs with a Doped Amorphous Hole Transport Layer and Operating Voltages Down to 3.2 V to Achieve 100 cd/m2,” Synthetic Metals, Vol. 127, No. 1-3, 2002, pp. 169-173. doi:10.1016/S0379-6779(01)00616-6
D. Gebeyehu, K. Walzer, G. He, M. Pfeiffer, K. Leo, J. Brandt, A. Gerhard, P. St?βel and H. Vestweber, “Highly Efficient Deep-Blue Organic Light-Emitting Diodes with Doped Transport Layers,” Synthetic Metals, Vol. 148, No. 2, 2005, pp. 205-2011. doi:10.1016/j.synthmet.2004.09.024
C. Adachi, R. Kwong, P. I. Djurovich, V. Adamovich, M. A. Baldo, M. E. Thompson and S. R. Forrest, “Endothermic Energy Transfer: A Mechanism For Generating Very Efficient High-Energy Phosphorescent Emission in Organic Materials,” Applied Physics Letters, Vol. 79, No. 13, 2001, pp. 2082-2085. doi:10.1063/1.1400076
H. Antoniadis, M. A. Abkowitz and B. R. Hsieh, “Carrier Deep—Trapping Mobility—Lifetime Products in Poly(p -phenylene vinylene),” Applied Physics Letters, Vol. 65, No. 16, 1994, pp. 2030-2032. doi:10.1063/1.112784
R. J. Holmes, B. W. D’Andrade, S. R. Forrest, X. Ren, J. Li and M. E. Thompson, “Efficient, Deep-Blue Organic Electrophosphorescence by Guest Charge Trapping,” Applied Physics Letters, Vol. 83, No. 18, 2003, pp. 3818- 3820. doi:10.1063/1.1624639
Y. Zheng, S.-H. Eom, N. Chopra, J. Lee, F. So and J. Xue, “Efficient Deep-Blue Phos-phorescent Organic Light-Emit- ting Device with Improved Electron and Exciton Confinement,” Applied Physics Letters, Vol. 92, No. 22, 2008, Article ID 223301. doi:10.1063/1.2937403
S.-J. Yeh, M.-F. Wu, C.-T. Chen, Y.-H. Song, Y. Chi, M.-H. Ho, S.-F. Hsu and C. H. Chen, “New Dopant and Host Materials for Blue-Light-Emitting Phosphorescent Organic Electroluminescent Devices,” Advanced Materi- als, Vol. 17, No. 3, 2005, pp. 285-289. doi:10.1002/adma.200401373
M.-H. Tsai, H.-W. Lin, H.-C. Su, T.-H. Ke, C.-C. Wu, F.-C. Fang, Y.-L. Liao, K.-T. Wong and C.-I. Wu, “Highly Efficient Organic Blue Electrophosphorescent Devices Based on 3,6-Bis(triphenylsilyl)carbazole as the Host Material,” Advanced Materials, Vol. 18, No. 9, 2006, 1216-1220. doi:10.1002/adma.200502283
S. Tokito, T. Iijima, Y. Suzuki, H. Kita, T. Tsuzuki and F. Sato, “Confinement of Triplet Energy on Phosphorescent Molecules for Highly-Efficient Organic Blue-Light-Emit- ting Devices,” Applied Physics Letters, Vol. 83, No. 3, 2003, pp. 569-571. doi:10.1063/1.1594834
P. A. Vecchi, A. B. Padmaperuma, H. Qiao, L. S. Sapochak and P. E. Burrows, “A Dibenzofuran-Based Host Material for Blue Electrophosphorescence,” Organic Letters, Vol. 8, No. 19, 2006, pp. 4211-4214. doi:10.1021/ol0614121
A. B. Padmaperuma, L. S. Sapochak and P. E. Burrows, “New Charge Transporting Host Material for Short Wave- length Organic Electrophosphorescence: 2,7-Bis (diphenyl- phosphine ox-ide)-9,9-dimethylfluorene,” Chemistry of Materials, Vol. 18, No. 9, 2006, pp. 2389-2396. doi:10.1021/cm0600677
L. S. Sapochak, A. B. Padmaperuma, P. A. Vecchi, H. Qiao and P. E. Burrows, “De-sign Strategies for Achieving High Triplet Energy Electron Transporting Host Materials for Blue Electrophosphorescence,” Proceedings of SPIE, May 2006, pp. 1-13.
T. Matsushima and C. Adachi, “Extremely Low Voltage Organic Light-Emitting Diodes with P-Doped Alpha-Sexi- thiophene Hole Transport and N-Doped Phenyldipyrenyl- phosphine Oxide Electron Transport Layers,” Applied Physical Letters, Vol. 89, No. 25, 2006, Article ID 253506. doi:10.1063/1.2410236
T. Oyamada, H. Sasabe, C. Adachi, S. Murase, T. Tominaga and C. Maeda, “Extremely Low-Voltage Driving of Organic Light-Emitting Diodes with a Cs-Doped Phenyl- dipyrenylphosphine Oxide Layer as an Elec-tron-Injection Layer,” Applied Physics Letters, Vol. 86, No. 3, 2005, Article ID 033503. doi:10.1063/1.1852707
L. Xiao, S.-J. Su, A. Agata, H. Lan and J. Kido, “Nearly 100% Internal Quantum Efficiency in an Organic Blue- Light Electrophosphorescent Device Using a Weak Electron Transporting Material with a Wide Energy Gap,” Advanced Materials, Vol. 21, No. 12, 2009, pp. 1271-1274. doi:10.1002/adma.200802034
“SADABS Version 2006: An Empirical Absorption Cor- rection Program,” Bruker AXS Inc., Madison, 2006.
O. Shimomura, T. Sato, I. Tomita, M. Suzuki and T. Endo, “Synthesis and Radical Polymerization of 2-Vinyldiben- zothiophene,” Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 35, No. 14, 1997, pp. 2813- 2819. doi:10.1002/(SICI)1099-0518(199710)35:14 3.0.CO;2-R
E. J. Bylaska, et al., “NWChem, A Computational Chemistry Package for Parallel Computer, Version 5.1,” A Modified Version, Pacific Northwest National Laboratory, Richland, 2007.
G. Black, et al., “ECCE, A Problem Solving Environment for Computational Chemistry, Software Version 6.0,” Pa- cific Northwest National Laboratory, Richland, 2009.
A. D. Becke, “Density-Fnnctional Exchange-Energy Approximation with Correct Asymptotic Be-havior,” Physical Reviews A, Vol. 38, No. 6, 1988, pp. 3098-3100. doi:10.1103/PhysRevA.38.3098
J. P. Perdew, “Density-Functional Approximation for the Correlation Energy of the Inhomogeneous Electron Gas,” Physical Reviews B, Vol. 33, No. 12, 1986, pp. 8822-8824. doi:10.1103/PhysRevB.33.8822
C. Lee, W. Yang and R. G. Parr, “Development of the Colic-Salvetti Correlation-Energy Formula into a Functional of the Electron Density,” Physical Reviews B, Vol. 37, No. 2, 1988, pp. 785-789. doi:10.1103/PhysRevB.37.785
B. Miehlich, A. Savin, H. Stoll and H. Preuss, “Results Obtained with the Correlation Energy Density Functionals of Becke and Lee, Yang and Parr,” Chemical Physics Letters, Vol. 157, No. 3, 1989, pp. 200-206. doi:10.1016/0009-2614(89)87234-3
A. D. Becke, “Density-Functional Thermochemistry. III. The Role of Exact Ex-change,” Journal of Chemical Physics, Vol. 98, No. 7, 1993, pp. 5648-5652. doi:10.1063/1.464913
W. J. Hehre, R. Ditchfield and J. A. Pople, “Self-Consistent Molecular Orbital Methods. XII. Fur-ther Extensions of Gaussian—Type Basis Sets for Use in Mo-lecular Orbital Studies of Organic Molecules,” Journal of Chemical Physics, Vol. 56, No. 5, 1972, pp. 2257-2261. doi:10.1063/1.1677527
M. M. Francl, W. J. Petro, W. J.; Hehre, J. S. Binkley, M. S. Gordon, D. J. DeFrees and J. A. Pople, “Self-Consistent Molecular Orbital Methods. XXIII. A Polarization- Type Basis Set for Second-Row Elements,” Journal of Chemical Physics, Vol. 77, No. 7, 1982, pp. 3654-3665. doi:10.1063/1.444267
D. Tanaka, Y. Agata, T. Takeda, S. Watanabe and J. Kido, “Ultra High Efficiency Green Organic Light-Emitting Devices,” Japanese Journal of Applied Physics, Vol. 46, 2007, pp. L117-L119. doi:10.1143/JJAP.46.L117
E. Polikarpov, P. K. Koech, L. Wang, J. S. Swensen, L. Cosimbescu, J. E. Rainbolt, A. L. Von Ruden, D. J. Gaspar and A. B. Padmaperuma, “Controlling Charge Transport in Blue OLEDs by Chemical Functionalization of Host Materials,” Journal of Photonics for Energy, Vol. 1, 2011, Article ID 011007-1. doi:10.1117/1.3528499
D. Kolosov, V. Adamovich, P. I. Djurovich, M. E. Thompson and C. Adachi, “1,8-Naphthalimides in Phosphores- cent Organic Leds: The Interplay Between Dopant, Exciplex, and Host Emission,” Journal of the American Chemical Society, Vol. 124, No. 33, 2002, pp. 9945-9954. doi:10.1021/ja0263588
A. Bree and R. Zwarich, “Electronic Spectra of Dibenzothiophene,” Spectrochimca Acta, Vol. 27A, No. 4, 1971, pp. 621-630. doi:10.1016/0584-8539(71)80264-7
E. Castellucci, P. Foffi and P. R. Salvi, “The Two-Photon Fluorescence Excitation Spectrum of Dibenzothiophene,” Chemical Physics, Vol. 63, No. 3, 1981, pp. 437-443. doi:10.1016/0301-0104(81)87018-8
J. Spanget-Larsen and E. W. Thulstrup, “The Electronic Transitions of Dibenzothiophene: Linear Dichroism Spectroscopy and Quantum Chemical Calculations,” Journal of Molecular Structure, Vol. 661-662, 2003, pp. 603-610. doi:10.1016/S0022-2860(03)00509-X
N. J. Turro, “Mod-ern Molecular Photochemistry,” University Science Books, Sausalito, 1991, pp. 146-148.
E. Polikarpov, J. S. Swensen, N. Chopra, F. So and A. B. Padmaperuma, “An Ambipolar Phosphine Oxide-Based Host for High Power Efficiency Blue Phosphorescent Organic Light Emitting Devices,” Applied Physics Letters, Vol. 94, No. 22, 2009, Article ID 223304. doi:10.1063/1.3148642
A. L. Von Ruden, L. Cosimbescu, E. Polikarpov, P. K. Koech, J. S. Swensen, J. T. Darsell and A. B. Padmape-ruma, “Phosphine Oxide Based Electron Transporting and Hole Blocking Materials for Blue Electrophosphorescent Organic Light Emitting Devices,” Chemistry of Materials, Vol. 22, No. 20, 2010, pp. 5678-5686. doi:10.1021/cm1013653
E. Polikarpov, J. S. Swensen, L. Cosimbescu, P. K. Koech, J. E. Rainbolt and A. B. Padmaperuma, “Emission Zone Control in Blue Organic Electrophosphorescent Devices through Chemical Modification of Host Materials,” Applied Physics Letters, Vol. 96, No. 5, 2010, Article ID 053306. doi:10.1063/1.3298556
S. Madhusoodhanan, E. Polikarpov, S. Garon and M. E. Thomp-son, “Crown Ether Dopants to Improve n-Type Doping of Electron Transport Layers,” Proceedings of the International Symposium on Super-Functionality Organic Devices, IPAP Conferences Series 6, 30 March 2005, pp. 110-113