Zl. Zhang et al., THRESHOLD LOWERING AND BY INTENSITY AND EFFICIENCY ENHANCEMENT BY DOPANTS IN POLYMER EMITTING DIODES, Chinese Physics Letters, 13(4), 1996, pp. 301-304
A new method to increase the luminance and quantum efficiency of polym
er light emitting diodes with a lower threshold voltage has been repor
ted. The threshold voltage, luminance and quantum efficiency have been
significantly improved by doping certain dopants with a lower highest
occupied molecular orbital (HOMO) level into the hole transporting la
yer. A high performance device has been achieved by addition of the pe
rylene and triphenylamine as a dopant into poly(N-vinylcarbazole). The
luminance and quantum efficiency increase by 2-3 times in comparison
with the undoped device, reaching 10000 cd/m(2) in luminance and 0.58%
in quantum efficiency. while threshold voltage is reduced to one half
value. Tile energy diagram has been obtained by measuring the HOMO le
vels and band gap values. Based on this, the carriers injection and ba
lance between electrons and holes as well as the action of dopant are
discussed.