High-efficiency blue-light-emitting diodes with narrow linewidth based on blends of poly[2-(2′-ethylhexyloxy)-1,4-phenylene] and poly(dialkylfluorene-co-dibenzothiophene)

High-efficiency blue light-emitting diodes were realized based on the blends of poly(dialkylfluorene-co-dibenzothiophene) in poly[2-(2′-ethylhexyloxy)-1,4-phenylene] host. The external quantum efficiency was increased by about four times, relative to devices with the guest polymer alone. Much more balanced carrier injection was assigned as the origin of the performance enhancement. Dramatic narrowing on linewidth, with the full width at half maximum reduced from more than 40 to 14.3 nm, produced more pure blue emission.