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

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• 作者：Erika Bellmann ; Sean E. Shaheen ; S. Thayumanavan ; Stephen Barlow ; Robert H. Grubbs ; Seth R. Marder ; Bernard Kippelen ; and Nasser Peyghambarian
• 刊名：Chemistry of Materials
• 出版年：1998
• 出版时间：June 1998
• 年：1998
• 卷：10
• 期：6
• 页码：1668 - 1676
• 全文大小：111K
• 年卷期：v.10,no.6(June 1998)
• ISSN：1520-5002

文摘

A series of poly(norbornenes) with pendant triarylamine (TPA)groups has been synthesizedby ring-opening metathesis polymerization and investigated as holetransport materials inorganic two-layer light-emitting diodes (LEDs). Efficient devicefabrication through spincasting of the hole transport layer (HTL) was possible, since thepolymers exhibited excellentfilm formation properties. LEDs of the formITO/poly(norbornene)-TPA/Alq₃/Mg (ITO =indium tin oxide, Alq₃ =tris(8-quinolinato)aluminum) showed bright green emissionwithexternal quantum efficiencies of up to 0.77% (1.30 lm/W) for 20 nmthick HTL films. Thelength and polarity of the linker between the triarylaminefunctionality and the polymerbackbone were varied systematically. The device performance wasfound to depend stronglyon these structural differences. Substitution of ester groups byless polar ether functionalitiesgreatly enhances external quantum efficiencies, lowers the operatingvoltage, and improvesthe stability of the device. Further improvement of the devicecharacteristics is achievedby reducing the length of the alkyl linker. The HTL can beconveniently cross-linked byUV irradiation. Cross-linking was found to decrease deviceperformance. A maximumexternal quantum efficiency of 0.37% was achieved for anAlq₃-LED with cross-linked HTL.