Effect of Drying Condition of Emitting Layer Formed by Ink-Jet Coating on Optical Property and Film Morphology of Polymer-Based Organic Light-Emitting Diodes

Abstract

The effect of a controlled drying process (CDP) of a polyfluorene [poly(9,9-dioctylfluorenyl)-2,7-diyl, PFO] based emitting layer formed by ink-jet coating on the optical properties and film morphologies of organic light-emitting diodes (OLEDs) was studied. The dominant wavelengths (DWLs) obtained from chromaticity shifted stepwise from 469 to 488 nm along neighboring cells of the emitting layer in a coating batch without the controlled drying process (without CDP). In contrast, the DWLs with the controlled drying process (with CDP), in which solvent mist is blown over the surface of the cell during ink-jet coating, did not show any chromaticity shift. The PFO film thicknesses measured using an optical interferometer also varied stepwise from 0.18 to 0.21 μm in neighboring cells in the coating batch without CDP, while those with CDP did not vary. Moreover, the surface profiles of each cell with CDP were flat and uniform. Therefore, we found that applying a CDP was effective in forming uniform PFO films with homogeneous optical properties.