OLED Efficiency Is Improved by Freeing Trapped Photons

An international research team led by Technische Universität Dresden (TU Dresden) has found a way to significantly boost OLED efficiency by extracting the trapped photons from OLEDs, which account for about 20% of the light particles that OLEDs generate.

To free trapped photons from white OLEDs, the researchers implemented nanostructures produced by reactive ion etching on a polydimethylsiloxane (PDMS) surface. They were able to control the topography of these quasi-periodic nanostructures by tuning the pretreatment conditions of the PDMS and the reactive ion etching treatment recipes. Mechanical deformations formed on the PDMS surface in response to compressive stress release initialized by the reactive ion etching with periodicity and depth distribution ranging from dozens of nm to µm.

Principle of reactive ion etching for the generation of quasi-periodic nanostructures. Courtesy of Sebastian Reineke et al., Nature Communications: CC BY 4.0.

The researchers demonstrated the possibility of tuning the average depth and the dominant periodicity of the nanostructures, adjusting the process parameters to achieve an optimal outcoupling structure for white OLEDs. When they integrated the nanostructures into a two-unit tandem white OLED, they realized an external quantum efficiency of up to 76.3% and a luminous efficacy of 95.7 lumens per watt. The team built an optical model that simulated the device’s performance.

According to the researchers, the use of reactive ion etching-induced nanostructures in white OLEDs has shown the capability to efficiently extract waveguide modes and surface plasmon polariton (SPP) modes, leading to a white OLED with higher efficiency, improved color stability, and more homogeneous radiance distribution. The nanostructures can be directly generated on a PDMS surface, making them compatible with emerging flexible devices. This controllable, scalable method to fabricate nanostructures could be a tool set for generating and manipulating nanostructures for use in other fields. “These quasi-periodic nanostructures are not only suitable as outcoupling structures for OLEDs, but also have the potential for further applications in optics, biology, and mechanics,” researcher Simone Lenk said.

The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-11032-z).