A New Near-Infrared Perovskite LED

Uniform electroluminescence from the new large-area flexible perovskite light-emitting diode. (Source: NUS / NPG)

Infrared LEDs are, conven­tionally, useful for optical communi­cations and covert illu­mination, and are commonly found in remote controls and security camera setups. They are generally small point sources, which limits their use if larger-area illumination is required in close proximity, for instance on a wearable device. Now, a research team led by Tan Zhi Kuang from the Department of Chemistry and the Solar Energy Research Institute of Singa­pore SERIS has developed high-efficiency near-infrared LEDs which can cover an area of 900 square millimeter using low-cost solution-processing methods.

This is several orders of magnitude larger than the sizes achieved in other reports, and opens up a range of interesting new appli­cations. Their devices employ a novel perovskite-based semi­conductor, which is a direct-bandgap semi­conductor that is capable of strong light emission. By using a new device archi­tecture, the research team is able to precisely tune the injection of electrons and holes into the perovskite, such that a balanced number of opposite charges could meet and give rise to efficient light generation. The team also found that this improve­ment allowed large-area devices to be made with signi­ficantly higher repro­ducibility.

Zhao Xiaofei, a Ph.D. student on the research team said, “We found that the hole-injection efficiency is a signi­ficant factor that affects the per­formance of the devices. By using an organic semi­conductor with a shallower ionisation potential as part of the device structure, we were able to improve the hole injection and achieve charge balance. This allowed our devices to emit light at efficiencies (external quantum efficiency of 20%) close to their theo­retical limit, and addi­tionally reduced the device-to-device per­formance variation, hence enabling the realisation of much larger devices.”

Tan said, “Some of the tech­nologies that our device could enable may include covert illu­mination in facial recog­nition or augmented reality/virtual reality eye-tracking tech­nologies. In particular, we have demons­trated that our LEDs could be suited for appli­cations involving subcutaneous deep-tissue illumination, such as in wearable health-tracking devices.” “These materials could also be developed to emit light in the full range of visible colours. They could therefore be applied in newer gene­rations of flat-panel electronic displays,” he added. (Source: NUS)

Reference: X. Zhao et al.: Large-area near-infrared perovskite light-emitting diodes, Nat. Phot., online 2 December 2019; DOI: 10.1038/s41566-019-0559-3

Link: Solar Energy Research Institute of Singapore, National University of Singapore NUS, Singapore, Singapore

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