Apparent activation energy; Electrochemical charge; Electron transport layers; Electrons and holes; Light emitting devices; Molecular electronic junction; Temperature dependence; Transport distances; Electronic, Optical and Magnetic Materials; Energy (all); Physical and Theoretical Chemistry; Surfaces, Coatings and Films; General Energy
Abstract :
[en] Bias-induced light emission and light-induced photocurrents were used as independent probes of charge transport in carbon-based molecular junctions containing Ru(bpy)3. The thickness, bias, and temperature dependence of both the total device current and photoemission were compared, as well as their response to bias pulses lasting from a few milliseconds to several seconds. The device current was exponentially dependent on the square root of the applied electric field, with weak dependence on thickness when compared at a constant field. In contrast, light emission was strongly dependent on thickness at a given electric field, with a thickness-independent onset for light emission and a large intensity increase when the bias exceeded the 2.7 V HOMO-LUMO gap of Ru(bpy)3. The apparent activation energies for light emission and current were similar but much smaller than those expected for thermionic emission or redox exchange. Light emission lagged current by several milliseconds but reached maximum emission in 5-10 ms and then decreased slowly for 1 s, in contrast to previously reported solid-state Ru(bpy)3 light-emitting devices that relied on electrochemical charge injection. We conclude that at least two transport mechanisms are present, that is, "unipolar injection" initiated by electron transfer from a Ru(bpy)3 HOMO to the positive electrode and "bipolar injection" involving hole and electron injection followed by migration, recombination, and light emission. The unipolar mechanism is field-driven and the majority of the device is current, while the bipolar mechanism is bias-driven and involves electrode screening by PF6 ions or mobile charges. In addition, significant changes in thickness and temperature dependence for thicknesses exceeding 15 nm imply a change from injection-limited transport to bulk-limited transport. The current results establish unequivocally that electrons and holes reside in the molecular layer during transport once the transport distance exceeds the ∼5 nm limit for coherent tunneling and that redox events involving nuclear reorganization accompany transport. In addition, they demonstrate luminescence in a single organometallic layer without hole or electron transport layers, thicknesses below 30 nm, and symmetric electrodes with similar work functions.
Disciplines :
Chemistry
Author, co-author :
Tefashe, Ushula M.; Department of Chemistry, University of Alberta, Edmonton, Canada
Van Dyck, Colin ; Université de Mons - UMONS > Faculté des Sciences > Service Chimie Physique Théorique
Saxena, Shailendra K. ; Department of Chemistry, University of Alberta, Edmonton, Canada
Lacroix, Jean-Christophe ; University de Paris, ITODYS, CNRS, UMR 7086, Paris, France
McCreery, Richard L. ; Department of Chemistry, University of Alberta, Edmonton, Canada
Language :
English
Title :
Unipolar Injection and Bipolar Transport in Electroluminescent Ru-Centered Molecular Electronic Junctions
Publication date :
05 December 2019
Journal title :
Journal of Physical Chemistry. C, Nanomaterials and interfaces
National Research Council Canada Agence Nationale de la Recherche University of Alberta Natural Sciences and Engineering Research Council of Canada Alberta Innovates
Funding text :
This work was supported by the University of Alberta, the National Research Council of Canada, and the Natural Sciences and Engineering Research Council and Alberta Innovates. ANR (France) is gratefully acknowledged for its financial support of this work (ANR-15-CE09-0001-01). Frederic Lafolet provided the Ru(bpy) 3 amino precursor essential for device fabrication.
Katsouras, I.; Najafi, A.; Asadi, K.; Kronemeijer, A. J.; Oostra, A. J.; Koster, L. J. A.; de Leeuw, D. M.; Blom, P. W. M. Charge Transport in Poly(P-Phenylene Vinylene) at Low Temperature and High Electric Field. Org. Electron. 2013, 14, 1591-1596, 10.1016/j.orgel.2013.03.025
Ringk, A.; Li, X.; Gholamrezaie, F.; Smits, E. C. P.; Neuhold, A.; Moser, A.; van der Marel, C.; Gelinck, G. H.; Resel, R.; de Leeuw, D. M.; Strohriegl, P. N-Type Self-Assembled Monolayer Field-Effect Transistors and Complementary Inverters. Adv. Funct. Mater. 2013, 23, 2016-2023, 10.1002/adfm.201202888
Defaux, M.; Gholamrezaie, F.; Wang, J.; Kreyes, A.; Ziener, U.; Anokhin, D. V.; Ivanov, D. A.; Moser, A.; Neuhold, A.; Salzmann, I.; Resel, R.; de Leeuw, D. M.; Meskers, S. C. J.; Moeller, M.; Mourran, A. Solution-Processable Septithiophene Monolayer Transistor. Adv. Mater. 2012, 24, 973-978, 10.1002/adma.201103522
Liao, C.; Yan, F. Organic Semiconductors in Organic Thin-Film Transistor-Based Chemical and Biological Sensors. Polym. Rev. 2013, 53, 352-406, 10.1080/15583724.2013.808665
Yang, X.; Zhou, G.; Wong, W.-Y. Functionalization of Phosphorescent Emitters and Their Host Materials by Main-Group Elements for Phosphorescent Organic Light-Emitting Devices. Chem. Soc. Rev. 2015, 44, 8484-8575, 10.1039/C5CS00424A
Fan, C.; Yang, C. Yellow/Orange Emissive Heavy-Metal Complexes as Phosphors in Monochromatic and White Organic Light-Emitting Devices. Chem. Soc. Rev. 2014, 43, 6439-6469, 10.1039/C4CS00110A
Braga, D.; Erickson, N. C.; Renn, M. J.; Holmes, R. J.; Frisbie, C. D. High-Transconductance Organic Thin-Film Electrochemical Transistors for Driving Low-Voltage Red-Green-Blue Active Matrix Organic Light-Emitting Devices. Adv. Funct. Mater. 2012, 22, 1623-1631, 10.1002/adfm.201102075
Sedghi, G.; Esdaile, L. J.; Anderson, H. L.; Martin, S.; Bethell, D.; Higgins, S. J.; Nichols, R. J. Comparison of the Conductance of Three Types of Porphyrin-Based Molecular Wires: β,meso,β-Fused Tapes, meso-Butadiyne-Linked and Twisted meso-meso Linked Oligomers. Adv. Mater. 2012, 24, 653-657, 10.1002/adma.201103109
Sedghi, G.; García-Suárez, V. M.; Esdaile, L. J.; Anderson, H. L.; Lambert, C. J.; Martín, S.; Bethell, D.; Higgins, S. J.; Elliott, M.; Bennett, N.; Macdonald, J. E.; Nichols, R. J. Long-Range Electron Tunnelling in Oligo-Porphyrin Molecular Wires. Nat. Nanotechnol. 2011, 6, 517-523, 10.1038/nnano.2011.111
Nguyen, Q. V.; Martin, P.; Frath, D.; Della Rocca, M. L.; Lafolet, F.; Bellinck, S.; Lafarge, P.; Lacroix, J.-C. Highly Efficient Long-Range Electron Transport in a Viologen-Based Molecular Junction. J. Am. Chem. Soc. 2018, 140, 10131-10134, 10.1021/jacs.8b05589
Yan, H.; Bergren, A. J.; McCreery, R.; Della Rocca, M. L.; Martin, P.; Lafarge, P.; Lacroix, J. C. Activationless Charge Transport across 4.5 to 22 Nm in Molecular Electronic Junctions. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 5326-5330, 10.1073/pnas.1221643110
Karipidou, Z.; Branchi, B.; Sarpasan, M.; Knorr, N.; Rodin, V.; Friederich, P.; Neumann, T.; Meded, V.; Rosselli, S.; Nelles, G.; Wenzel, W.; Rampi, M. A.; von Wrochem, F. Ultrarobust Thin-Film Devices from Self-Assembled Metal-Terpyridine Oligomers. Adv. Mater. 2016, 28, 3473-3480, 10.1002/adma.201504847
Taherinia, D.; Smith, C. E.; Ghosh, S.; Odoh, S. O.; Balhorn, L.; Gagliardi, L.; Cramer, C. J.; Frisbie, C. D. Charge Transport in 4 nm Molecular Wires with Interrupted Conjugation: Combined Experimental and Computational Evidence for Thermally Assisted Polaron Tunneling. ACS Nano 2016, 10, 4372-4383, 10.1021/acsnano.5b08126
Smith, C. E.; Odoh, S. O.; Ghosh, S.; Gagliardi, L.; Cramer, C. J.; Frisbie, C. D. Length-Dependent Nanotransport and Charge Hopping Bottlenecks in Long Thiophene-Containing Π-Conjugated Molecular Wires. J. Am. Chem. Soc. 2015, 137, 15732-15741, 10.1021/jacs.5b07400
Tefashe, U. M.; Nguyen, Q. V.; Morteza Najarian, A.; Lafolet, F.; Lacroix, J.-C.; McCreery, R. L. Orbital Control of Long-Range Transport in Conjugated and Metal-Centered Molecular Electronic Junctions. J. Phys. Chem. C 2018, 122, 29028-29038, 10.1021/acs.jpcc.8b09978
Morteza Najarian, A.; Bayat, A.; McCreery, R. L. Orbital Control of Photocurrents in Large Area All-Carbon Molecular Junctions. J. Am. Chem. Soc. 2018, 140, 1900-1909, 10.1021/jacs.7b12577
Tuccitto, N.; Ferri, V.; Cavazzini, M.; Quici, S.; Zhavnerko, G.; Licciardello, A.; Rampi, M. A. Highly Conductive 40-Nm-Long Molecular Wires Assembled by Stepwise Incorporation of Metal Centres. Nat. Mater. 2009, 8, 41-46, 10.1038/nmat2332
Van Nguyen, Q.; Lafolet, F.; Martin, P.; Lacroix, J. C. Ultrathin Molecular Layer Junctions Based on Cyclometalated Ruthenium Complexes. J. Phys. Chem. C 2018, 122, 29069-29074, 10.1021/acs.jpcc.8b10766
Sedghi, G.; Sawada, K.; Esdaile, L. J.; Hoffmann, M.; Anderson, H. L.; Bethell, D.; Haiss, W.; Higgins, S. J.; Nichols, R. J. Single Molecule Conductance of Porphyrin Wires with Ultralow Attenuation. J. Am. Chem. Soc. 2008, 130, 8582-8583, 10.1021/ja802281c
Kalyuzhny, G.; Buda, M.; McNeill, J.; Barbara, P.; Bard, A. J. Stability of Thin-Film Solid-State Electroluminescent Devices Based on Tris(2,2 -Bipyridine)Ruthenium(Ii) Complexes. J. Am. Chem. Soc. 2003, 125, 6272-6283, 10.1021/ja029550i
Buda, M.; Kalyuzhny, G.; Bard, A. J. Thin-Film Solid-State Electroluminescent Devices Based on Tris(2,2 -Bipyridine)Ruthenium(Ii) Complexes. J. Am. Chem. Soc. 2002, 124, 6090-6098, 10.1021/ja017834h
Liu, C.-Y.; Bard, A. J. Individually Addressable Submicron Scale Light-Emitting Devices Based on Electroluminescence of Solid Ru(Bpy)3(Clo4)2 Films. J. Am. Chem. Soc. 2002, 124, 4190-4191, 10.1021/ja0256156
Maness, K. M.; Masui, H.; Wightman, R. M.; Murray, R. W. Solid State Electrochemically Generated Luminescence Based on Serial Frozen Concentration Gradients of RuIII/II and RuII/I Couples in a Molten Ruthenium 2,2′-Bipyridine Complex. J. Am. Chem. Soc. 1997, 119, 3987-3993, 10.1021/ja9636754
Handy, E. S.; Pal, A. J.; Rubner, M. F. Solid-State Light-Emitting Devices Based on the Tris-Chelated Ruthenium(II) Complex. 2. Tris(Bipyridyl)Ruthenium(II) as a High-Brightness Emitter. J. Am. Chem. Soc. 1999, 121, 3525-3528, 10.1021/ja984163n
Gao, F. G.; Bard, A. J. Solid-State Organic Light-Emitting Diodes Based on Tris(2,2 -Bipyridine)Ruthenium(II) Complexes. J. Am. Chem. Soc. 2000, 122, 7426-7427, 10.1021/ja000666t
Zhao, W.; Liu, C.-Y.; Wang, Q.; White, J. M.; Bard, A. J. Effect of Residual Solvent on Ru(Bpy)3(Clo4)2-Based Light-Emitting Electrochemical Cells. Chem. Mater. 2005, 17, 6403-6406, 10.1021/cm050375p
Rudmann, H.; Rubner, M. F. Single Layer Light-Emitting Devices with High Efficiency and Long Lifetime Based on Tris(2,2′ Bipyridyl) Ruthenium(II) Hexafluorophosphate. J. Appl. Phys. 2001, 90, 4338-4345, 10.1063/1.1409577
Lee, J. K.; Yoo, D. S.; Handy, E. S.; Rubner, M. F. Thin Film Light Emitting Devices from an Electroluminescent Ruthenium Complex. Appl. Phys. Lett. 1996, 69, 1686-1688, 10.1063/1.117028
Tefashe, U. M.; Nguyen, Q. V.; Lafolet, F.; Lacroix, J.-C.; McCreery, R. L. Robust Bipolar Light Emission and Charge Transport in Symmetric Molecular Junctions. J. Am. Chem. Soc. 2017, 139, 7436-7439, 10.1021/jacs.7b02563
Morteza Najarian, A.; Szeto, B.; Tefashe, U. M.; McCreery, R. L. Robust All-Carbon Molecular Junctions on Flexible or Semi-Transparent Substrates Using "Process-Friendly" Fabrication. ACS Nano 2016, 10, 8918-8928, 10.1021/acsnano.6b04900
Ivashenko, O.; Bergren, A. J.; McCreery, R. L. Light Emission as a Probe of Energy Losses in Molecular Junctions. J. Am. Chem. Soc. 2016, 138, 722-725, 10.1021/jacs.5b10018
Ivashenko, O.; Bergren, A. J.; McCreery, R. L. Monitoring of Energy Conservation and Losses in Molecular Junctions through Characterization of Light Emission. Adv. Electron. Mater. 2016, 2, 1600351, 10.1002/aelm.201600351
Chandra Mondal, P.; Tefashe, U. M.; McCreery, R. L. Internal Electric Field Modulation in Molecular Electronic Devices by Atmosphere and Mobile Ions. J. Am. Chem. Soc. 2018, 140, 7239-7247, 10.1021/jacs.8b03228
Morteza Najarian, A.; McCreery, R. L. Structure Controlled Long-Range Sequential Tunneling in Carbon-Based Molecular Junctions. ACS Nano 2017, 11, 3542-3552, 10.1021/acsnano.7b00597
Shen, Y.; Hosseini, A. R.; Wong, M. H.; Malliaras, G. G. How to Make Ohmic Contacts to Organic Semiconductors. ChemPhysChem 2004, 5, 16-25, 10.1002/cphc.200300942
Fereiro, J. A.; Kondratenko, M.; Bergren, A. J.; McCreery, R. L. Internal Photoemission in Molecular Junctions: Parameters for Interfacial Barrier Determinations. J. Am. Chem. Soc. 2015, 137, 1296-1304, 10.1021/ja511592s
Fereiro, J. A.; McCreery, R. L.; Bergren, A. J. Direct Optical Determination of Interfacial Transport Barriers in Molecular Tunnel Junctions. J. Am. Chem. Soc. 2013, 135, 9584-9587, 10.1021/ja403123a
Das, B. C.; Szeto, B.; James, D. D.; Wu, Y.; McCreery, R. L. Ion Transport and Switching Speed in Redox-Gated 3-Terminal Organic Memory Devices. J. Electrochem. Soc. 2014, 161, H831-H838, 10.1149/2.0831412jes
Das, B. C.; Pillai, R. G.; Wu, Y.; McCreery, R. L. Redox-Gated Three-Terminal Organic Memory Devices: Effect of Composition and Environment on Performance. ACS Appl. Mater. Interfaces 2013, 5, 11052-11058, 10.1021/am4032828
Sze, S. M.; Ng, K. K. Physics of Semiconductor Devices. 2 nd ed.; Wiley: New York, 1981.
Ranganathan, S.; Murray, R. W. Comparison of Thermal and Optical Electron-Transfer Barriers in Ruthenium Redox Polyether Melts. J. Phys. Chem. B 2004, 108, 19982-19989, 10.1021/jp046310b
Züfle, S.; Altazin, S.; Hofmann, A.; Jäger, L.; Neukom, M. T.; Brütting, W.; Ruhstaller, B. Determination of Charge Transport Activation Energy and Injection Barrier in Organic Semiconductor Devices. J. Appl. Phys. 2017, 122, 115502, 10.1063/1.4992041
Kordt, P.; van der Holst, J. J. M.; Al Helwi, M.; Kowalsky, W.; May, F.; Badinski, A.; Lennartz, C.; Andrienko, D. Modeling of Organic Light Emitting Diodes: From Molecular to Device Properties. Adv. Funct. Mater. 2015, 25, 1955-1971, 10.1002/adfm.201403004
Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Electron Transport Materials for Organic Light-Emitting Diodes. Chem. Mater. 2004, 16, 4556-4573, 10.1021/cm049473l
