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

Abstract

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 50 nm was approximately 41-fold that of a conventional OLED with a current flow region of 4 mm2. 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.

Organic Lasers: Recent Developments on Materials, Device Geometries, and Fabrication Techniques

“…It has recently been shown experimentally that OLEDs with 50 nm diameter electrodes retain higher external quantum efficiency at large current densities than larger OLEDs and that current densities (40-fold improvement in critical current density for EQE roll-off). 285,286 However, we like to point out that for realizing electrically pumped organic lasers, the dimensions of the OLED should probably not be smaller than the lateral extension of the mode supported by the structure (characteristics size, > λ/2) as this would lead to a small overlap between the laser mode and the pumped region of the device which will lead to reduced modal gain.…”

Emerging Biomedical Applications of Organic Light‐Emitting Diodes

“…In order to increase drive currents further, designs should consider methods to reduce thermal load by using substrates with high thermal conductivity and by reducing the active area. [83,138,[145][146][147] A reduction of the active area down to nanoscopic sizes (50-200 nm) furthermore reduces exciton annihilation, which may strongly reduce efficiency roll-off and thus improve light output at high drive currents. [83,147] However, the required device area is often determined by the application and the attachment of heat sinks is hardly possible for flexible, wearable, or transparent devices.…”

Investigating underlying mechanism in spectral narrowing phenomenon induced by microcavity in organic light emitting diodes

“…However, developing lasing actions from thin film OLEDs has been a long-term challenging endeavor 7–9 . The technical difficulties that prevent the electrically pumped lasing actions are essentially due to the absence of cooperative light-emitting states caused by the energy loss associated with triplets 10, 11 , quenching of light-emitting states from polarons 12 , and insufficient pumping densities from electrical injection 13, 14 . In contrast, optical pumping has led to significant lasing actions in organic semiconductors by using different optical feedback mechanisms based on microcavities and grating designs to realize cooperative Frenkel excitons with significant photoluminescence (PL) spectral narrowing phenomenon as increasing pumping density 9, 15, 16 .…”