1P074
Characterization of optoelectronic devices based on the methylene-linked
compounds of pyrene(RIES, Hokkaido University) Md. Dalilur Rahaman, Toshifumi Iimori, Tatsuo Hamada, andNobuhiro Ohta
[Introduction] Organic light-emitting diodes (OLEDs) and organic light emitting field effecttransistor (OLEFET) have been identified as dominant technology after the breakthroughmade by Tang and VanSlyke1 and A. Hepp2 for the applications of future optoelectronic
devices. Although pyrene is the blue-emitting chromophore, investigation focused on using
methylene-linked compounds of pyrene, i.e., pyrene-(CH2)n-pyrene, where n = 1, 2, 3, 4, 5, as
emitters for OLEDs is very limited. On the contrary, the electron-transfer process and carrier
mobility of electron and/or hole are different in the pyrene-(CH2)n-pyrene and unsubstituted
pyrene, because the intermolecular and intramolecular electron-transfer process and carrier
mobility are different.3 The efficacy of inducing enhanced carrier mobility in a short linkage
of methylene chain is very high.3 Therefore, the electron-transfer process and carrier mobility
in pyrene-(CH2)n-pyrene through the methylene bond might have the significant impact forincreasing the performance of molecular devices. In the present study, we fabricate the OLEDand OLEFET using pyrene-(CH2)n-pyrene compounds to investigate the electroluminescencedependence depending on the methylene chain length variation, and the fundamental role ofthe methylene chain length on the performance of the molecular devices.
[Experimental] Figure 1 represents cell configurationand the molecular structure of the materials used inthis study. OLED was fabricated on indium-tin-oxide

BCPN(ITO) coated glass substrate. The chamber pressure-4was 2.5 x 10

Pa during deposition of the organicNNNNCH3CH3!-NPDNNt-Bu

TAZ

1, 3-bis-(1-pyrenyl) propanematerials and metal. The deposited organic layers
consisted of a hole transport layer (HTL) of N, Ndiphenyl-N, N-bis(1-naphthyl)-1, 1-biphenyl-4, 4diamine (!-NPD), a blue emission layer (EML) ofAl
TAZ-01BCP
Py-(CH2)n-Py!-NPDITO
Glass

methylene-linked compounds of pyrene, i. e.,

Fig.1: Schematic diagram of EL cell andpyrene-(CH2)n-pyrene, hole blocking layer (HBL)

molecular structures of materials usedof 2, 9-Dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP), and an electron transport layer(ETL) of 3-(4-Biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1, 2, 4-triazole (TAZ-01). Then,finally, a ~ 400 nm thick aluminum layer was deposited. The thickness of all the materials
layers were controlled by the co-deposition controller. Current density-voltage-luminance (JV-L) characteristics were recorded simultaneously with the measurements of the EL spectraby using the spectrometer (Ocean Optics) and a digital multimeter (IWATSU, VOAC7520).
[Results and Discussion] Figure 2 (a) and 2(b) show the J-V-L characteristics of Glass/ITO(150 nm)/!-NPD (65 nm)/Py-3-Py (40 nm)/BCP (55 nm)/TAZ-01(40 nm)/Al (400 nm) cell.
The current increases above the bias voltage of 8 V,
anda large current density of " 1 mA/cm2 isobtained at 15 V. Light was emitted from the device
above the bias voltage of 8 V, and the luminance ofthe device increased with the bias voltage (Fig.
2(b)). The maximum luminance of " 3000 cd/cm2was observed at 15 V. Figure 2 (c) shows theelectroluminescence (EL) spectra of the device as
depicted in Fig. 1. It is clearly evident that the EL
intensity of the device increases with the increase of
the applied voltage, because the mobility isincreased with the electric field. The device

Fig.2: Current-voltage characteristics (a),exhibited bright blue EL with an emission peakluminance-voltage characteristics (b), andat

EL spectrum (c) of Glass/ITO/!-approximately

490

nm.

We

have

successfully demonstrated high luminance

NPD/Pyrene-(CH2)3-Pyrene/BCP/TAZ/Al

OLED with the exploitation of the methylene-linked compounds of pyrene. It is revealed thatthe pyrene-(CH2)3-pyrene compounds exhibit the bright blue electroluminescence more than3000 cd/cm2 as well as from the practical point of view it would be one of the best hostmaterials for OLED and OLEFET devices. The fabrication of the OLEFET by using thePyrene-(CH2)n-Pyrene with different value of n is under investigation.
References
1. C.W. Tang, S.A. VanSlyke, Appl. Phys. Lett. 51 (1987) 913.
2. A. Hepp, H. Heil, W. Weise, M. Ahles, R. Schmechel and H. von Seggern, Phys. Rev.
Lett. 91 (2003) 157406.
3. N. Otha, H. Kawabata, S. Umeuchi, and I. Yamazaki, Chem. Phys. Lett. 310 (1999)
397