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Title: Enhanced hole injection and transport in molybdenum-dioxide-doped hole-transporting layers
Authors: Matsushima, Toshinori
Adachi, Chihaya
Issue Date: 2008-02-01
Publisher: American Institute of Physics
Magazine name: Journal of Applied Physics
Volume: 103
Number: 3
Start page: 034501-1
End page: 034501-8
DOI: 10.1063/1.2836972
Abstract: We have found that molybdenum dioxide (MoO_2) is an excellent dopant for enhancing electrical conductivities in organic hole-transporting layers. We fabricated hole-only devices with an alpha-sexithiophene (α-6T) layer doped with MoO_2 at various concentrations to investigate how doping MoO_2 into the α-6T layers influences the hole-injection and hole-transport characteristics of these layers. We observed a marked increase in electrical conductivity as a result of the MoO_2 doping. The 30-mol % MoO_2-doped α-6T layer had a high electrical conductivity of 8.9±1.3×10^<-6> S/cm. From the results of our visible/near-infrared absorption spectra study of these doped layers, we confirmed that this increase in electrical conductivity is caused by a charge transfer between MoO_2 and α-6T, which leads to an increase in free hole concentration in the doped layers and the formation of an ohmic contact at an electrode/α-6T interface. In the latter part of this paper, we discuss current flow and electroluminescence (EL) characteristics of organic light-emitting diodes (OLEDs) with a 30-mol % MoO_2-doped α-6T hole-transporting layer and a 30-mol % Cs-doped phenyldipyrenylphosphine oxide (POPy_2) electron-transporting layer. We achieved an extremely low driving voltage of 3.1 V required for a current density of 100 mA/cm^2 in the doped OLEDs owing to the use of the α-6T and POPy_2 layers with high carrier mobilities and the excellent p-type MoO_2 and n-type Cs dopants. We demonstrated the enhancement of power efficiencies by ≈2 times in the doped OLEDs compared with undoped OLEDs and observed bright EL at low driving voltages in the doped OLEDs, for example, 100 cd/m^2 at 2.3 V, 1000 cd/m^2 at 2.7 V, and 10 000 cd/m^2 at 3.3 V.
Rights: Copyright 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Toshinori Matsushima, Chihaya Adachi, Journal of Applied Physics, 103(3), 034501 (2008) and may be found at http://link.aip.org/link/?JAPIAU/103/034501/1
URI: http://hdl.handle.net/10119/8540
Material Type: publisher
Appears in Collections:c10-1. 雑誌掲載論文 (Journal Articles)

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