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

Carrier-transport control is a critical factor in achieving high performance of organic light-emitting devices (LEDs). We have compared hole conduction between polydiphenylacetylene (PDPA) derivatives without and with a carrier-transport moiety, such as poly[1-(p-n-butylphenyl)-2-phenylacetylene] (PDPA-nBu) and poly[1-(p-n-carbazolyphenyl)-2-phenylacetylene] (PDPA-Cz), respectively. Hole transport is studied by current–voltage measurements and fitted using the space-charge limited current model. It is shown that the hole mobility can be improved several orders of magnitude by attaching carbazolyl side groups to the PDPA back bone (PDPA-Cz), as compared to that of PDPA-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.