Researchers develop flexible, water-resistive OLED display

Transparent and flexible displays, which have received attention in various fields including automobile displays and bio-healthcare, are known to break easily when experiencing small deformations. To solve this problem, research is being conducted on transparent and flexible conductive materials such as carbon nanotubes, graphene, silver nanowires and conductive polymers. A team of researchers from KAIST Engineering have now developed a water-resistant, transparent and flexible OLED using MXene technology. The material can emit and transmit light even when exposed to water.

MXene is a 2D material with high electrical conductivity and optical transmittance, and it can be produced on a large scale through solution processes. However, despite these properties, MXene’s applications are limited as a long-term electrical device due to its electrical properties being degraded easily by atmospheric moisture and water. The material was therefore unable to be systemised into the form of a matrix that can display information.

A team of researchers led by Professor Kyung Cheol Choi used an encapsulation tactic that can protect materials from oxidation caused by moisture and oxygen to develop an MXene-based OLED with a long lifespan and high stability against external environmental factors. The researchers analysed the degradation mechanism of MXene’s electrical conductivity, then designed an encapsulation membrane. The team blocked moisture and provided flexibility through residual stress offset, ultimately producing a double-layered encapsulation membrane. In addition, a thin plastic film with a thickness of a few micrometres was attached to the top layer to allow washing in water without degradation.

The researchers developed a MXene-based red(R)/green(G)/blue(B) OLED that emits a brightness of over 1000 cd/m² that is detectable to the naked eye even under sunlight, thereby meeting the conditions for outdoor displays. For the red MXene-based OLED, the researchers confirmed a standby storage life of 2000 hours (under 70% luminescence), a standby operation life of 1500 hours (under 60% luminescence) and a flexibility withstanding 1000 cycles under a low curvature of under 1.5 mm.

The researchers showed that the red MXene-based OLED’s performance was maintained after six hours of immersion under water (under 80% luminescence). A patterning technique was also used to produce the MXene-based OLED in the form of a passive matrix, and the team demonstrated its use as a transparent display by displaying letters and shapes. PhD candidate So Yeong Jeong, who led this study, said the researchers produced an adequate encapsulation structure and a suitable process design to improve the reliability of the MXene OLED. “By producing a matrix-type MXene OLED and displaying simple letters and shapes, we have laid the foundations for MXene’s application in the field of transparent displays,” Jeong said.

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