Flexible OLED displays now achieved with new thin-film MoS2 transistors

By Jean-Jacques
DeLisle, contributing writer

A
team of South Korean researchers from Yonsei University and Chung-Ang
University have announced
a breakthrough in organic light emitting diode (OLED) technology and the
creation of flexible OLED screens. This development could have wide-ranging
applications across many tech industries. According to the recently published paper, the
researchers have overcome many of the barriers which previously prevented
flexible OLED screens in the past. The researchers have proposed a new
architecture for OLEDs which greatly increases charge mobility and flexibility.

 

Image source: Yonsei University.

 

The new OLED display works by using molybdenum disulfide
(MoS2), a material which has been extensively researched and classified as a
semiconductor but, until now, has never been applied to OLED technology. The
problem with using MoS2 in OLED screens is caused by its large-scale contact
resistance. This contact resistance causes an electrical resistance in the
areas where the MoS2 contacts other metals, causing a loss of energy and
efficiency. It also makes the material lose much of its efficiency when bent or
folded due to Coulomb scattering and trap charges at the interface between the
gate dielectric and MoS2. Thus, lowering charge mobility to under 1 cm2 V−1 s−1
on par with that of a-H Si, which made its use as a flexible screen nearly
impossible.

 

In order to overcome this obstacle, researchers have
rearranged the architecture of the OLED completely, sandwiching a
microscopically thin layer of MoS2 between two thin sheets of high-k dielectric aluminum oxide (Al2O3).
This new modified switching device architecture is proposed for efficiently
exploiting the high-k dielectric
Al2O3 layer, which, when integrated in an active matrix, can drive the
ultrathin OLED display even in dynamic folding states. According to the
researchers heading the project, the high-k
Al2O3 layer reduces the contact resistance at the metal/MoS2 interface,
creating an innovative design that facilitates considerable n-type doping of
the MoS2 layer, owing to its oxygen-deficient surface. This development on
previous modules allows for the reduction of the scattering charge impurities. Additionally,
the lower layer of Al2O3 layer reduces surface roughness, a feature that can
further improve the performance of devices as it effectively decreases the
interface-trapped charge density.

 

What
this all amounts to is a flexible, efficient, LED screen which can be folded up
and unfolded, over and over again, without losing efficiency or breaking. So
far, these South Korean researchers have already created a six by six OLED
display using this technology, and it is designed to be flexible and attached
to the wrist as a display for wearable technology. Possible future applications
with this creative invention are endless, and we can expect to see this
technology making its way into cell phones with flexible screens that will
never crack or break. Televisions could wrap around corners or contour to odd
surfaces with ease. OLED displays are already all around us, and with the
flexibility offered by this new breakthrough, we can expect to see them in even
more places in the years to come.