Paper-thin LEDs that are kinder to the eye

A new, experimental LED is nearly as thin as paper and emits a warm, sun-like glow.

The design, developed by scientists reporting in ACS Applied Materials & Interfaces, could be used in next-gen phone and computer screens as well as other lighting applications — all while minimising sleep disruption caused by harsh artificial light.

“This work demonstrates the feasibility of ultrathin, large-area quantum dot LEDs that closely match the solar spectrum,” said Xianghua Wang, a corresponding author on the study. “These devices could enable next-generation eye-friendly displays, adaptive indoor lighting, and even wavelength-tunable sources for horticulture or wellbeing applications.”

To achieve indoor lighting that feels natural and soothing, earlier approaches have used flexible LEDs with red and yellow phosphorescent dyes to mimic a candle-like warmth. A newer alternative relies on quantum dots — tiny semiconductor particles that transform electrical energy into coloured light. Some research teams have already used quantum dots to make white LEDs, but replicating the complete spectrum of sunlight has remained difficult, particularly in the yellow and green regions where sunlight is strongest.

To address this challenge, Lei Chen and colleagues developed quantum dots that could recreate that balanced, sun-like glow in a thin, white quantum dot LED (QLED). Meanwhile, Wang’s group proposed an efficient conductive material design that could operate effectively at relatively low voltages.

The team began by synthesising red, yellow–green and blue quantum dots coated with zinc–sulfur shells. They determined the precise colour ratio needed to match the spectrum of natural sunlight as closely as possible. Next, they assembled the QLED on an indium tin oxide glass substrate, layering conductive polymers, the quantum dot blend, metal oxide particles, and finally a top coating of aluminium or silver. The quantum dot layer measured only a few dozen nanometres in thickness — much thinner than standard colour conversion layers — resulting in a white QLED with an overall profile comparable to wallpaper.

In initial tests, the slim QLED performed best under a 11.5 V power supply, which enabled it to give off the maximum bright, warm white light. This light had more intensity in red wavelengths and less intensity in blue wavelengths, which is better for sleep and eye health, according to the researchers. Objects illuminated by the QLED also appeared close to their true colours, scoring over 92% on the colour rendering index.

In subsequent experiments, the researchers made 26 white QLED devices, using the same quantum dots but different electrically conductive materials to optimise the operating voltage. These light sources required only 8 V to reach maximum light output, and about 80% exceeded the target brightness for computer monitors.

The researchers received funding from the National Natural Science Foundation of China, the Natural Science Foundation of Anhui Province, and the Major Science and Technology Special Project of Zhongshan City. Their paper can be read at DOI: 10.1021/acsami.5c10632.

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