Suppression of external quantum efficiency roll-off of nanopatterned organic-light emitting diodes at high current densities

We developed organic light-emitting diodes (OLEDs) with nanopatterned current flow regions using electron-beam lithography with the aim of suppressing singlet-polaron annihilation (SPA). Nanopatterns composed of lines and circles were used in the current flow regions of nano-line and nano-dot OLEDs, respectively. Excitons partially escape from the current flow regions where SPA takes place. As such, current densities where external quantum efficiencies were half of their initial values (J₀) increased as line width and circle diameter were decreased to close to the exciton diffusion length. Circles were more efficient at enhancing exciton escape and increasing J₀ than lines. The J₀ increase in the nano-dot OLEDs containing nanopatterned circles with a diameter of 50nm was approximately 41-fold that of a conventional OLED with a current flow region of 4mm². The dependence of J₀ on the size and shape of the nanopatterns was well explained by an SPA model that considered exciton diffusion. Nanopatterning of OLEDs is a feasible method of obtaining large J₀.