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

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,C-3,C-](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 lm/W at 802 cd/m(2) and a maximum brightness of 11 800 cd/m(2). 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.