Low operating voltage bright organic light-emitting diode using iridium complex doped in 4,4′-bis[N-1-napthyl-N-phenyl-amino]biphenyl

A low driving voltage organic light-emitting diode using a yellow phosphor bis[2-(4-tert-butylphenyl)benzothiazolato-N,C2′] iridium (acetylacetonate) as a dopant and 4,4′-bis[N-1-napthyl-N-phenyl-amino]biphenyl as a host was fabricated. The device without p- or n-doped transporting layer shows a turn-on voltage as low as 2.45V, and a luminance of 1000cd∕m2 at 4.3V. A maximum luminance of 23230cd∕m2 at 10V was achieved. The decrease of the device turn-on voltage may result from direct charge carrier trapping in the dopant and hole only transporting characteristic of the host material. Both charge carrier trapping and energy transfer mechanisms were found in the electroluminescence process.