Fluorescent polymer guest:small molecule host solution-processed OLEDs

TitleFluorescent polymer guest:small molecule host solution-processed OLEDs
Publication TypeJournal Article
Year of Publication2013
AuthorsHellerich ES, Intemann JJ, Cai M, Liu R, Ewan MD, Tlach BC, Jeffries-El M, Shinar R, Shinar J
Journal TitleJournal of Materials Chemistry C
Date Published09/14
Type of ArticleArticle
ISBN Number2050-7526
Accession NumberWOS:000322911900002
Keywordselectrophosphorescent devices, ENERGY-TRANSFER, high-efficiency, LAYER, LIGHT-EMITTING-DIODES, mobility, performance, single, transporting materials

Solution-processed OLEDs with polymer hosts and polymer or small-molecule guests have been studied extensively. More recently, efficient solution-processed OLEDs with small molecule hosts and small molecule guests were also reported. However, small molecule hosts of polymer guests in solution-processed fluorescent OLEDs have not been investigated. In this work guest: host systems consisting of the small molecule 4,4'-bis(9-carbazolyl)-biphenyl (CBP) as host to polymer guests such as novel benzobisoxazole (BBO)-containing copolymers and well-known poly(2-methoxy-5-(2'-ethyl-hexyloxy)1,4-phenylene vinylene) (MEH-PPV) are compared to those with poly(N-vinyl carbazole) (PVK) host, which previously yielded highly efficient phosphorescent OLEDs. In the case of MEH-PPV, guest: host OLEDs are also compared to those with a neat MEH-PPV emitting layer. It is found that replacing the polymer host PVK with the small molecule host CBP improves efficiencies by up to 100%. A blue emissive BBO-polymer: CBP device reaches a luminous efficiency (eta(L,max)) of 3.4 cd A(-1) (external quantum efficiency eta(ext) = 2.4%), while the PVK-based device exhibits eta(L,max) 1.7 cd A(-1) (eta(ext) = 1.2%). A green emissive BBO:CBP OLED exhibits eta(L,max) = 5.7 cd A(-1) (eta(ext) = 2.1%), while that in the PVK host is 3.1 cd A(-1) (eta(ext) = 1.1%). For MEH-PPV: CBP these values are 3.7 cd A(-1) (eta(ext) = 1.4%), compared to 2.9 cd A(-1) (eta(ext) = 1.0%) for MEH-PPV:PVK and 0.7 cd A(-1) (eta(ext) = 0.4%) for the neat MEH-PPV device. Possible origins of the improvement are discussed, including increased charge mobility, smoother film morphology, and the potential effect of multiple non-coiling host small molecules (in contrast to the likely coiled PVK) surrounding a polymer guest.

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