Efficient blue-green and white light-emitting electrochemical cells based on poly[9,9-bis(3,6-dioxaheptyl)-fluorene-2,7-diyl]

Abstract

Efficient blue-green polymer light-emitting electrochemical cells, based on poly[9,9-bis(3,6-dioxaheptyl)-fluorene-2,7-diyl] (BDOH-PF), have been demonstrated. BDOH-PF has a high photoluminescent quantum efficiency of 73% photon/photon in solid films. The polyether-type side groups of this polymer are built in to promote the ionic conductivity necessary for the operation of light-emitting electrochemical cells (LECs). Blue-green LECs using a blend of BDOH-PF and lithium triflate as the emissive layer, ITO and Al as the electrodes, achieve an external quantum efficiency of 4% photons/electron and a luminous efficiency of 12 lm/W at 3.1 V. The brightness reaches ∼200 cd/m2 at 3.1 V, and exceeds 1000 cd/m2 at 3.5 V. When additional poly(ethylene oxide) (PEO) is blended into the emissive layer, phase separation between PEO and BDOH-PF occurs, and the emission becomes white. These white emitting LECs reach an external quantum efficiency of 2.4% photons/electron and 400 cd/m2brightness at a bias of 4 V.