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Please use this identifier to cite or link to this item: http://hdl.handle.net/10119/10282

Title: Optical, morphological, structural, electrical, molecular orientation, and electroluminescence characteristics of organic semiconductor films prepared at various deposition rates
Authors: Matsushima, Toshinori
Shiomura, Koutaro
Naka, Shigeki
Murata, Hideyuki
Keywords: Organic light-emitting diode
High deposition rate
Photoluminescence quantum yield and lifetime
Time-of-flight charge carrier mobility
Molecular orientation
Issue Date: 2011-10-01
Publisher: Elsevier
Magazine name: Thin Solid Films
Volume: 520
Number: 6
Start page: 2283
End page: 2288
DOI: 10.1016/j.tsf.2011.09.060
Abstract: Extremely high deposition rates of ≈7200 nm s^<-1> for N,N´-diphenyl-N,N´-bis(1-naphthyl)-1,1´-biphenyl-4,4´-diamine (a-NPD) and of ≈1700 nm s^<-1> for tris(8-hydroxyquinoline)aluminum (Alq_3) are found to be possible by controlling source-substrate distances and crucible temperatures. Shapes of ultraviolet-visible absorption spectra and photoluminescence (PL) spectra, atomic force microscope images, X-ray diffraction patterns, PL quantum yields, PL lifetimes, and PL radiative decay rates of the films remain independent of the deposition rates ranging from 0.01 to 1000 nm s^<-1>. On the other hands, hole currents of hole-only α-NPD devices increase ≈3 times while electron currents of electron-only Alq_3 devices decrease by ≈1/60 as the deposition rates are increased from 0.01 to 10 nm s^<-1>. The increase in hole current is confirmed to arise from an increase in hole mobility of α-NPD measured using a time-of-flight technique. The increase in hole moility is probably due to a parallel orientation of an electronic transition moment of α-NPD at the higher deposition rates. Moreover, the three orders of magnitude increase in deposition rate from 0.01 to 10 nm s^<-1> of α-NPD and Alq_3 results in a relatively small increase in voltage of ≈15% and a decrease in external quantum efficiency of ≈30% in organic light-emitting diodes (OLEDs). The reduction of the OLED performance is attributable to the marked decrease in electron current relative to the slight increase in hole current, indicating a decrease in charge balance factor at the higher deposition rates.
Rights: NOTICE: This is the author's version of a work accepted for publication by Elsevier. Toshinori Matsushima, Koutaro Shiomura, Shigeki Naka, Hideyuki Murata, Thin Solid Films, 520(6), 2011, 2283-2288, http://dx.doi.org/10.1016/j.tsf.2011.09.060
URI: http://hdl.handle.net/10119/10282
Material Type: author
Appears in Collections:c10-1. 雑誌掲載論文 (Journal Articles)

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