Researchers at the National University of Singapore (NUS) have developed highly efficient, large-area and flexible perovskite-based near-infrared LEDs for new wearable device technologies.

High-efficiency PeLEDs by NUS image

The 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 mm2 using low-cost solution-processing methods. This is several orders of magnitude larger than the sizes achieved in previous reports, and opens up a range of new applications.

Their devices employ a perovskite-based semiconductor. By using a new device architecture, the research team is able to precisely tune the injection of electrons and holes (negative and positive charges) 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 PhD 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 ionization 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 realization 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 colors. They could therefore be applied in newer generations of flat-panel electronic displays,” he added.

Source: 
Tags: