Princeton University

School of Engineering & Applied Science

Advances in Large-Area Nanopatterning by Nanoimprint Lithography and Applications in Light-Emitting Devices

Ji Qi
Prof. Chou
Engineering Quadrangle J-401
Thursday, July 12, 2018 - 2:30pm to 4:00pm

As an advanced nanolithography method, the unique of nanoimprint lithography (NIL) enables creating complicated nanoscale structures in a low-cost, high-throughput way. One of NIL’s most promising applications is in light-emitting devices. By integrating the specially-designed nanostructures into the device structures, the device performances can be significantly enhanced compared to that using conventional device structures.
Organic light emitting diode (OLED), as an emerging light-emitting device, draws great attention in recent years due to its potential application in lighting and display panel. One of the central challenges of OLED is the light extraction efficiency. For a conventional OLED device structure, only 20%~30% of generated photons are extracted from the device. In the first part of my talk, two novel nanostructure substrates designed and fabricated by NIL will be introduced: (a) a dielectric nanomesh and (b) a flat metamaterial micro-lens array. By implementing them in OLEDs, the highest light extraction efficiency was enhanced over 100% compared to the control device.
Another challenge of OLED is the transparent electrode. Conventional ITO electrodes used in OLEDs are rigid which are not compatible with fabricating OLEDs on flexible substrates. And the transmissivity and conductivity of ITO electrodes are not very good. Hence, in the second part of my talk, a metallic film with nanostructures (MESH) is developed to replace the conventional ITO electrodes. And a novel nanoprinting technique based on NIL is developed to fabricate MESH on flexible substrates (e.g., PDMS). In terms of optical and electrical properties, MESH electrodes on PDMS achieve a figure-of-merit (FoM) of 182, whereas ITO on PET only has a FoM of 25.