Bright and efficient blue and green light-emitting diodes based on conjugated polymer blends

We report the use of green and blue fluorene conjugated polymers doped with hole transport materials consisting of triarylamine copolymers to fabricate bright and efficient blue and green single-layer light-emitting diodes (LEDs). These blends show enhanced quantum and power efficiency, much higher brightness and current densities and lower turn on and operating voltages compared with undoped devices. Optimised blue emission devices exhibited a maximum brightness of 1550 cd/m(2), a maximum external electroluminescence quantum efficiency of 0.9 cd/A or 0.4% and a maximum power efficiency of 0.3 lm/W. Optimised green emission devices showed a maximum brightness of 7400 cd/m(2), a maximum external electroluminescence quantum yield of 0.9% or 2.75 ed/A and a maximum power efficiency of 0.64 lm/W at high brightness. (C) 2000 Elsevier Science S.A. All rights reserved.