Improvement of efficiency and colour purity of red-dopant organic light-emitting diodes by energy levels matching with the host materials

By using a series of tris-(8-hydroxyquinoline) metal chelates with central metal ions of Al³⁺, Ga³⁺, In³⁺ as the host materials, red organic light-emitting diodes have been fabricated, which used a red fluorescent dye, 4-(dicyanomethylene)-2-t-butyl-6-(8-methoxy-1,1,7,7-tetramethyljulolidyl- 9-enyl)4H-pyran (DCJMTB), as the emitter or guest dopant material. The doped devices with Gaq₃ as the host materials produce high efficiencies and saturated red colour chromaticity. The device (1% DCJMTB doped in Gaq₃) showed a current efficiency of 2.64 cd A^-1, which is about 40% higher than that of the doped Alq₃ device, and nearly two times higher than that of the doped Inq₃ device at 1% DCJMTB dopant concentration. The colour coordinates of the Gaq₃:1% DCJMTB device in the Commission internationale del'Eclairage chromaticity chart are x = 0.63 and y = 0.36.