Hole transport in substituted polydiphenylacetylene light-emitting devices: mobility improvement through carbazole moiety

Carrier-transport control is a critical factor in achieving high performanc e of organic light-emitting devices (LEDs). We have compared hole conductio n between polydiphenylacetylene (PDPA) derivatives without and with a carri er-transport moiety, such as poly[1-(p-n-butylphenyl)-2-phenylacetylene] (P DPA-nBu) and poly[1-( p-n-carbazolyphenyl)-2-phenylacetylene] (PDPA-Cz), re spectively. Hole transport is studied by current-voltage measurements and f itted using the space-charge limited current model. It is shown that the ho le mobility can be improved several orders of magnitude by attaching carbaz olyl side groups to the PDPA back bone (PDPA-Cz), as compared to that of PD PA-nBu. The electroluminescence is studied and compared in heterostructured LEDs using PDPA-nBu and PDPA-Cz as hole-transport layers. It is found that carrier transport and balance have significant roles in the performance of the substituted PDPA-based electroluminescent devices. (C) 2000 Elsevier S cience S.A. All rights reserved.