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Investigation of spacer influences in phosphorescent-emitting nonconjugated PLED systems

: Thesen, M.W.; Krueger, H.; Janietz, S.; Wedel, A.; Graf, M.


Journal of polymer science. A, polymer chemistry 48 (2010), Nr.2, S.389-402
ISSN: 0360-6376
ISSN: 0887-624X
Fraunhofer IAP ()

An assay was introduced to clarify influences on electroluminescent behavior for RGB-colored phosphorescent terpolymers with N,N-Di-p-tolyl-aniline as hole-transporting unit, 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (tert-BuPBD) as electron-transporting unit, and different iridium complexes in RGB-colors as triplet emitting materials. All monomers were attached with spacer moieties to the "para" position of a polystyrene. Polymer light emitting diodes (PLEDs) were built to study the electro-optical behavior of these materials. The gist was a remarkable influence of hexyl-spacer units to the PLED performance. For all three colors only very restricted PLED performances were found. In comparison RGB-terpolymers were synthesized with directly attached charge transport materials to the polymer backbone. For this directly linked systems efficiencies were 28 cd A(-1) @ 6 V (green), 4.9 cd A(-1) @ 5 V (red) and 4.3 cd A(-1) @ 6 V (bluish). In summary we assume that an improved charge percolation pathways regarding to the higher content of semiconducting molecules and an improved charge transfer to the phosphorescent dopand in the case of the copolymers without spacers are responsible for the better device performance comparing the copolymers with hexyl spacers. The approach of the directly connected charge transport materials at the nonconjugated styrene polymer backbone should be favored for further investigations, therefore.