Comparison of Device Performance in Two Thin-Film Electroluminescent Devices Made of Vacuum-Sublimed Dye Film and Spin-Coated Polymer Film

Abstract

Electroluminescent (EL) characteristics in EL devices made of vacuum-sublimed dye films and spin-coated polymer films were compared. Low-molar-mass dye, 9,10-bis[4-(N,N-diphenylamino)styryl]anthracene (dye-BSA), for the preparation of vacuum-sublimed films, and polymer with 9,10-bis[4-(N,N-diphenylamino)-styryl]anthracene chromophore linked with alkylether groups (polymer-BSA) were employed. Single-layer devices, indium-tin oxide (ITO)/dye-BSA/MgAg and ITO/polymer-BSA/MgAg were prepared, and EL performances were compared. Double-layer devices which have an oxadiazole derivative (OXD-7) electron transport layer, ITO/dye-BSA/OXD-7/MgAg and ITO/polymer-BSA/OXD-7/MgAg, were also prepared. The current density-voltage relationships between dye-BSA devices and polymer-BSA devices were considerably different mainly due to the poor film quality of polymer-BSA. The comparisons of the luminance-current density relationships of the devices with two classes of BSA films showed that the polymer-BSA devices exhibited similar EL characteristics as the dye-BSA devices in the region of current density higher than 10 mA/cm2. The possibility of the use of common material design concept for low-molar-mass materials and polymers was discussed.

New Triarylamine-Containing Polymers as Hole Transport Materials in Organic Light-Emitting Diodes: Effect of Polymer Structure and Cross-Linking on Device Characteristics

“…Figure shows the structures of two widely studied triarylamines. Their hole transport properties have been investigated, − and they have been used in organic LEDs. ,− Triarylamine-based HTLs are most commonly prepared by vapor deposition of the molecular material. ,− Polymeric host−guest systems 1,15 and covalent incorporation of triarylamine into polymers 16-20 have also been reported.

1 Structures of commonly used organic hole transport materials.

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High Mobility Hole Transport Fluorene-Triarylamine Copolymers

“…Recent synthesis activity has focused on the development of materials, often oligomers [19] and starburst compounds, [17] that possess i) a higher glass transition temperature, leading to enhanced stability, and ii) a better match of their highest occupied molecular orbital energies with the work function of ITO, offering the possibility of an ohmic contact. [18] Work reported on polymers includes side-chain systems, [20] main-chain copolymers with saturated spacers, [21,22] network polymers with oligomeric conjugated units, [23] and fully conjugated homo- [24] and copolymers. [25] Mobility data have not, however, been presented for these latter materials.…”

Organic light-emitting diodes using an in situ thermally polymerized hole transporting layer

“…4 To solve these problems, the approach of using covalent attachment of triarylamines onto polymers has been employed. [5][6][7] In addition, hightemperature processing of crystalline TPD hole transporting layers has also been reported. 8 Compared to the conventional devices with amorphous organic layers prepared at room temperature, the devices prepared at higher temperatures had shown considerable improvements in luminescent efficiency, brightness, as well as storage stability in air.…”