Nov 15, 2017: Researchers at the Korea Advanced Institute of Science & Technology (KAIST) have designed fabric-based OLEDs that would be comfortable to wear as a functional clothing.
They published a paper ‘Highly Flexible and Efficient Fabric-Based Organic Light-Emitting Devices for Clothing-Shaped Wearable Displays’ in Scientific Reports, that highlights identical electrical and optical performance levels for the fabric-based OLED compared with a glass-based OLED.
They used a soft fabric that is made from heat-resistant polyethylene naphthalate (PEN) fibers as the substrate. They thermally laminated a thin planarization sheet onto the fabric through a roll-to-roll process, which was aimed to reduce surface roughness to a couple of nanometres.On top of this, they layered a functional 200nm-thick OLED.
The planarization sheet integrated a gas barrier of 1.5 dyads to prevent the permeation of water vapour and oxygen. The sheets had a moisture barrier property of about 10−3 g/m2/day.
They then created an OLED stack of two metal electrodes, carrier injection and transport layers, an emission layer with a host-guest system, and an out-coupling layer.
According to the published paper, a maximum luminance and a current efficiency of 93,030 cd/m2 and 49.14 cd/A for non-encapsulated fabric-based OLEDs was created, which can be compared with 169959 cd/m2 and 64.45 cd/A respectively for the glass-based OLEDs.
By adding MoO3/NPB/MoO3 encapsulation layers, they could yield a maximum current efficiency of 70.43 cd/A and a luminance of 35,844 cd/m2 for their fabric-based OLED.
The device on the fabric operated after bending at a radius of 2mm for 3,000 cycles and a bending radius of 1cm after 30,000 cycles.
When it bended at 1mm radius, the leakage current occurred within the devices, and crack patterns like the weave patterns of the fabric, appeared on the OLED cell.
KAIST researchers expect that such fabric-based OLEDs would be able to integrate various e-textile industries, such as in the manufacturing of curtains and tablecloths and in automobiles as well as in the fashion and healthcare industries.