Spontaneous buckling in flexible organic light-emitting devices for enhanced light extraction

Abstract

We herein present the results of a study of the direct fabrication of buckled patterns in flexible organic light-emitting devices (FOLEDs) that had a conducting polymer anode on a polyethersulfone substrate. These patterns were produced spontaneously by the thermal deposition of an aluminum cathode on an electroluminescent (EL) composite layer. The polymer used for the anode was modified poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and the EL layer was composed of a solution-processable small molecular composite including phosphorescent Iridium complex mixed with a poly(vinylcarbazole) host. It is shown that FOLEDs produced with buckled patterns can exhibit a luminance as high as ca. 14,900 cd/m(2) with a peak efficiency of 50.5 cd/A. The patterned structure formed by the buckling of the EL layer allows FOLEDs to be produced with a high peak external quantum efficiency of 15% with an increase in light extraction by a factor of ca. 3.1. These results show that spontaneous buckling yields patterned structures that offer considerable promise for the production of high performance, reproducible and reliable FOLEDs.