Emission properties of organic light-emitting diodes directly patterned using optically controlled nanostructuration means

Abstract

In a classical multilayer organic light emitting diode (OLED) structure, almost 80% of the light emitted happens to be lost following guiding through the different layers. Patterning of the OLEDs structure was already proposed and reported as an interesting solution towards the optimization of an OLED external efficiency. As an alternative to classical lithographic patterning methods which appear to be quite complex, we propose here the implementation of a quite direct and easy-to-set light-induced patterning method using azo-dye polymers. When a polymer film containing azobenzene dyes is irradiated by an interference pattern between polarized laser beams at a wavelength near the chromophore absorption band, the film surface undergoes a direct, reversible and controlled topographic modification. More surprisingly, we have recently experimentally evidenced that uniform irradiation of an azo-dye polymer using a single laser beam with normal incidence onto the polymer film surface could lead to a self structuration process resulting in the formation of a quasi hexagonal surface-relief grating. After a description of the main features related to light-induced surface relief gratings, we show here that this original patterning process offers an interesting solution for control and optimisation of optoelectronic devices such as OLEDs. The guiding properties of both 1D and 2D structures have been studied and their effects on the light emission properties of a patterned electroluminescent polymer have been characterized and compared after angle dependent measurement of the photoluminescence spectrum. Quite efficient decoupling is evidenced.