Improving the power efficiency of white light-emitting diode by doping electron transport material

Highly efficient white light emission was realized via the partial energy transfer from blue host polyfluorene (PF) to orange light emission dopant rubrene. A more balanced charge transport was achieved by adding an electron transport material, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), into the PF-rubrene system to enhance the electron transportation. Efficiency improvement by as much as a factor of 2 has been observed through the addition of PBD. These devices can easily reach high luminance at low driving voltages, thus achieving high power efficiency at high luminance (14.8, 13.5, and 12.0 lm/W at the luminances of 1000, 2000, and 4000 cd/m(2), respectively). Therefore, this performance is an important approach toward solid-state lighting application. The enhancement is mainly attributed to three factors: increased electron transport property of the host material, increased photoluminescence quantum efficiency, and the shifting of emission zone away from cathode contact. The reported efficiency is among the highest values reported in the white emission polymer light-emitting diodes. (c) 2006 American Institute of Physics.