Efficient white polymer light-emitting diodes based on the control of a emissive polymer morphology through solvent processing

We present the results of a systematic study on how the solvent processing affects the EL properties of a single emissive layer white PLED based on a polyfluorene derivative polymer. The EL spectrum of the device using solvent processing, peaked at 436, 572 nm, shows a pure white emission and the luminous efficiency is enhanced, which is attributed to the presence of the crystalline polyfluorene induced by solvent processing. The crystalline polyfluorene that acts as the self-dopant enhances the blue emission and increases the purity of the white light. Most importantly, the charge transport is balanced after solvent processing, which favors improving the luminous efficiency. A light-emitting efficiency of 12 cd/A is achieved after solvent processing, about 50% increase compared to the as-spin-coated device. (c) 2010 Published by Elsevier B.V