Recently, there have been attempts to make nanoscale OLEDs by isolating active materials in-between insulating materials such as silicon dioxide. These studies show the viability of patterning active OLED materials in an insulating layer to produce light from sub-micron-scale pixels. Unfortunately, the fabrication routes to making such devices typically involve processes that ultimately lead to charge spreading, resulting in much larger emissive areas than intended.

Isolating the emission

Researchers at the University of Texas at Dallas, US, are using nano-imprint lithography (NIL) to prepare electronically isolated nanoscale OLEDs. The fabrication process, which is described in the journal Nanotechnology, involves directionally evaporating the small molecule materials NPB and Alq3 into nano-imprinted SU-8 nanochannels with vertical sidewalls to avoid charge spreading. A cross-sectional electron micrograph shows physically isolated active materials deposited in the SU-8 channels.

The team compared its nanochannel design with micro-scale devices and found that device performance is retained as the dimensions are reduced to the nanoscale. Furthermore, the scientists applied surface potential microscopy (SPM) to reveal a periodicity in potential on the surfaces of devices without metal electrodes (see image), which indicates electrical separation of active materials and, therefore, isolated light emission from the nanoscale confined OLEDs.