Swiss researchers design ultra-pure green paper-thin LEDs

September 08, 2017 // By Julien Happich
Chemical engineers from ETH Zurich have produced what they believe to be the purest green with an ultra-slim, bendable light-emitting diode. Their research stems from the need for improved colour quality in next generation ultra-high definition displays.

Publishing their results in Nano Letters under the title "Ultrapure Green Light-Emitting Diodes Using Two-Dimensional Formamidinium Perovskites: Achieving Recommendation 2020 Color Coordinates", the researchers strived to meet the 2020 standard requirement with an optimized LED device whose color gamut covers 97% and 99% of the Rec. 2020 standard in the CIE 1931 and the CIE 1976 color space, compared to today's TV displays which cover on average only 73 to 78 percent of these color spaces.

The paper details the design of colloidal two-dimensional (2D) formamidinium lead bromide (FAPbBr3) hybrid perovskites with an engineered dielectric quantum well (DQW), showing a high exciton binding energy of 162 meV, and a photoluminescence quantum yield of about 92% in spin-coated films.

Being able to produce a green light 99 percent pure, together with existing red and blue light technologies, will allow a richer range of colours to be displayed, with finer hues.


Produced at room temperature, ETH's pure green
LED is flexible and bendable.

Until now, the researchers explain, because the human eye is able to distinguish between more intermediary green hues than red or blue ones, there would always be perceivable color shortcomings due to the lack of a pure green light source.

What's more, as well as being ultra-thin and bendable, the device was obtained using simple room-temperature processes, making it possible to industrialize their production through a low-cost roll-to-roll process.

Before any commercialization though, the researchers have yet to improve the efficiency of their materials as well as their lifespan, nevertheless, a patent was filed for their new approach.

ETH Zurich - www.ethz.ch