Efficient pure-white organic light-emitting diodes with a solution-processed, binary-host employing single emission layer

Abstract

Efficient white light-emitting diodes were fabricated with a solution-processed single emission layer composing a molecular and polymeric materials mixed binary host. The main host used was a molecule of 4, 4′ -bis-(carbazol-9-yl) biphenyl and the assisting host used was a blue light-emitting polyfluorene-derived copolymer of poly[(9,9-dioctylfluo-renyl-2, 7-diyl)-alt-co-(9-hexyl-3,6-carbazole)]. The hosts were doped via solution-mixing a green dye of tris(2-phenylpyridine) iridium (III) and a red dye of bis[2- (2′ -benzo-thienyl)-pyridi-nato- N, C3,] (acetylacetonate) iridium (III). One resultant device having a pure white emission of Commission Internationale de l'Eclairage (0.33, 0.33) has a maximum power efficiency of 4.2 lmW at 802 cd m2 and a maximum brightness of 11 800 cd m2. The better efficiency performance may be attributed to the addition of the assisting host, which halves the energy barrier for holes to inject into the light-emitting zone. © 2006 American Institute of Physics.