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 fabricat e bright and efficient blue and green single-layer light-emitting diodes (L EDs). These blends show enhanced quantum and power efficiency, much higher brightness and current densities and lower turn on and operating voltages c ompared with undoped devices. Optimised blue emission devices exhibited a m aximum brightness of 1550 cd/m(2), a maximum external electroluminescence q uantum 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.