Two-Dimensional TiO₂ honeycomb structure for enhanced light extraction from polymer light-emitting diodes

We have demonstrated the preparation of an ordered hole pattern via a simple colloidal assembly technique and a sol-gel process without the use of any special equipment to enhance light extraction from polymer light-emitting diodes (LEDs). From two-dimensional (2D) polystyrene (PS) colloidal crystals, 2D TiO2 honeycomb structures were easily obtained after depositing TiOx sol solution onto the colloidal crystals by a doctor blade technique and removing the PS colloidal particles. In order to optimize the thickness of the deposited TiOx materials for fabricating 2D TiO2 honeycomb structures, the concentration of the TiOx sol solution was controlled. By applying the 2D TiO2 honeycomb structure on the backside of the glass substrate, the efficiency of a polymer LED, compared to the device without the structure, was increased without a significant change in the electroluminescence spectrum. This enhancement is attributed to the improved light extraction, which is due to the suppression of total internal reflection at the interface between the glass substrate and the air.