Abstract
Efficient white-light-emitting polymers were developed through the incorporation
of narrow-bandgap green-emitting and red-emitting siloles moieties into the
blue-emitting fluorene and carbazole copolymers backbone. By carefully controlling the
concentrations of the green- and red-emitting species in the resulting copolymers, a
white-light emission was achieved due to the simultaneous emission from all three
colors. EL devices based on the copolymers exhibited luminance efficiencies of 4.87 cd/A
with color coordinates of (0.30, 0.31) that was very close to the ideal CIE chromaticity
coordinates for pure white light of (0.33, 0.33). After thermal treatment under 160
°C, the devices showed the best luminous properties with external quantum yield of
3.39%, <i>L</i><sub>ELmax</sub> of 6.78 cd/A and color coordinate of (0.29, 0.30).
Furthermore, the color coordinates remained almost unchanged over the range of operating
potentials. The main operating process involve in the white electroluminescent process
can be attributed to the direct charge trapping on the narrow band gap units and partial
energy transfer from the blue-emitting segments to the green- and red-emitting siloles
moieties.
© 2013 IEEE
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