Bright and colour stable white polymer light-emitting diodes

Bright and efficient white-polymeric light-emitting diodes (WPLED) were fabricated using poly(2-(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene) (MEH-PPV) doped in poly(fluorene) (PF) with an architecture of ITO/PEDOT/MEH-PPV : PF(0.6 wt%)/Ba/Al. At low doping levels, blue emission from PF and yellow emission from MEH-PPV co-existed in photoluminescence (PL) spectra, because of incomplete energy transfer from the PF to the MEH-PPV. When the weight ratio of the PF to the MEH-PPV is set at 0.6%, the device exhibits stable white electroluminescence (EL) with CIE coordinates from (0.36, 0.36) to (0.32, 0.35) and brightness from 200 cd m(-2) to 10000 cd m(-2) as the forward bias increases from 5 V to 10 V. The device characterizations show that the EL turn-on voltage is below 4 V and the maximum luminance reaches 10270 cd m(-2) at the bias of 10 V. The luminous power efficiency and luminous efficiency were found to be about 1.8 lm W-1 and 2.3 cd A(-1), respectively, at the bias of 4 V.