Effects of singlet and triplet energy transfer to molecular dopants in polymer light-emitting diodes and their usefulness in chromaticity tuning

Efficient, white emission with Commission Internationale de L'Eclairage coordinates of 0.33, 0.42 is demonstrated from polymer light-emitting diodes operating at high brightness. An amino endcapped polyfluorene derivative doped with rubrene was used as the active layer, in combination with a poly(3,4-ethylenedioxythiophene) hole transport layer. Luminescence reaches 14950 Cd/m(2) at a current density of 150 mA/cm(2), and the maximum external quantum efficiency measured 1.05% for a bias voltage of 9.0 V. We observe a fall in external quantum efficiency relative to the undoped device, which we ascribe to an increased singlet-triplet annihilation rate at the dopant sites. (C) 2001 American Institute of Physics.