25 Aug 2020

NUS researchers have developed transparent near-infrared light-emitting diodes (LEDs) that could be integrated into the displays of smart-watches, smart-phones and augmented or virtual reality devices.

Near-infrared (NIR) covert illumination is increasingly important for facial recognition, motion sensing and depth sensing functions in mobile devices. However, these NIR illumination sources, which are usually non–transparent LED chips, occupy valuable space and could lead to unsightly black notches on an otherwise full-area colour display.

A research team led by Prof TAN Zhi Kuang from the Department of Chemistry and the Solar Energy Research Institute of Singapore (SERIS), NUS has developed efficient NIR LEDs that are highly-transparent, with an average transmittance of more than 55% across the visible spectrum. Their devices employ an ultra-thin layer of a novel perovskite-based semiconductor, which is capable of intense and efficient light emission. This perovskite semiconductor also benefits from low-cost processing and versatile integration into a variety of device substrates. By further replacing the traditional non-transparent metallic electrode with a new electrode comprising layers of ultra-thin metals and conductive oxide, the team is able to achieve an optimal balance of high optical transparency, low electrode resistance, and efficient charge injection that are required for the LED to generate light efficiently.

Mr XIE Chenchao, a Ph.D. student on the research team said, “We found that the implementation of a thin aluminium interlayer in our transparent electrode greatly reduced plasma damage to our device during the electrode deposition process, and allowed our devices to function efficiently.”

Prof Tan said, “NIR technologies have made significant inroads into wearable, mobile, gaming and augmented reality gadgets in recent years, and have seen uses ranging from security to health-tracking and 3D sensing. We believe that our transparent NIR LED concept could open up an exciting array of new advanced functionalities in small wearable devices which were previously unattainable with traditional III-V semiconductor LED chips. For instance, we may one day be able to apply this technology in smart-watches for facial recognition, or use this for high-security contactless payment.”

As a proof of concept, the team has demonstrated a transparent LED that is overlaid across a smart-watch display to provide intense NIR illumination (see figure below).

20 Dec 2019

PhD students from our group has won 4 presentation and poster awards at the Asian Crystallographic Association Conference (AsCA 2019).

• Cheryldine Q. X. Lim (Poster Award)
• Jun De Andrew Ng (Presentation & Poster Award)
• Chenchao Xie (Poster Award)

Congratulations for this achievement!

2 Dec 2019

NUS researchers have developed highly efficient, large-area and flexible near-infrared light-emitting diodes (LEDs) for new wearable device technologies.

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.

A research team led by Prof TAN Zhi Kuang from the Department of Chemistry and the Solar Energy Research Institute of Singapore (SERIS), NUS 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 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 (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.

Mr 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.”

Prof 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.

27 Nov 2019

Kang Rui Garrick Lim has won the prestigious Thomas Clarkson Gold Medal at The Global Undergraduate Awards in Dublin for his work on NIR-emitting quantum dots.

undergraduateawards.com/winners/global-winners-2019

Congratulations for this excellent achievement!

18 Jul 2019

Nanolumi, a Singapore-based advanced materials company, announced today it has secured US$1 million in seed funding to support the commercialisation of emerging technologies in their portfolio, starting with perovskite quantum dot technology which the company exclusively licenses from the National University of Singapore (NUS), Asia’s top university for chemistry.

Perovskite quantum dots are high performing semi-conductive nanocrystals with the unique emissive properties to re-create all colours in the visible spectrum, offering true-to-life colours that are extremely bright, pure and vivid; attributes that make the advanced material ideal for powering immersive displays, anti-counterfeit prevention, bioimaging and other smart lighting applications.

The funding will fuel customer acquisition, team expansion and the company’s mission to accelerate the adoption of emerging technologies by translating breakthrough research and late-stage R&D projects from the lab into products and applications for the market. Nanolumi aims to be a lab-to-market leader for advanced materials by focusing on market-led innovations, an approach where solutions are developed based on a clear understanding of the opportunities and most urgent challenges faced by the industry, as well as by establishing strategic partnerships that minimise product development time and designing products mindfully to ensure they are cost competitive, scalable and compatible with existing supply chains.

“High capital costs, long product development cycles and an intensive spec-in process are uncertainties that often deter investments in advanced materials. The financing is a validation of our mission, business approach and technologies,” said Jax Lee, CEO and Co-founder, Nanolumi. “As Singapore continues her transformation to be a key node for technology, innovation and enterprise in Asia and around the world, we are proud that Nanolumi is positioned to support these goals through employment opportunities and an export-driven manufacturing business.”

18 Jul 2019

Kang Rui Garrick Lim, an outstanding honours year research student at our lab, has received 5 prestigious awards during the 2019 NUS commencement ceremony.

1. GlaxoSmithKline Gold Medal
2. Pfizer Medal
3. SNIC Medal
4. Outstanding Undergraduate Researcher Prize
5. Singapore National Institute of Chemistry Book Prize

Congratulations on this well-deserved achievement! He will be embarking on his PhD journey at Harvard University.

9 Jul 2018

NUS researchers have developed a colour-enhancement film that could bring richer and more natural colours to next-generation flat-panel electronic displays.

Current commercial display technologies such as OLEDs (organic light-emitting diodes) and QLED (quantum dot light-emitting diodes) can only produce slightly more than 50% of the colours visible to the human eye. This limits the colour reproduction that these displays can achieve.

A research team led by Prof TAN Zhi Kuang from the Department of Chemistry and the Solar Energy Research Institute of Singapore (SERIS) at NUS has developed a colour-enhancement film that could allow future display technologies to produce more than 75% of all visible colours. This technology is enabled by a semiconductor material known as perovskites, which can be tuned by changing its chemical composition to emit light strongly and efficiently in a variety of colours. To make the enhancement films, the research team mixed nanometre-sized crystals of the perovskite material with a liquid monomer (precursor of plastics), and triggered a polymerisation reaction by illuminating the mixture with white light. This process allowed the team to fabricate a strongly luminescent perovskite-polymer composite film that possesses a threefold enhancement in luminescence efficiency compared to a conventional perovskite nanocrystal film. The improved luminescence performance is a result of the increased spatial separation between the perovskite nanocrystals in the polymer composite material, which prevents the channelling of energy between crystals to the defective and non-emissive ones. This innovation allows perovskite materials to emit light more efficiently and consume less energy when deployed in a display product. Their colour performance can enable next-generation televisions and monitors to achieve the higher quality Rec. 2020 colour standard for ultra-high definition television (UHDTV), compared to the more limited DCI-P3 standard in current displays (see Figure below).

In order to understand how displays produce a range of colours, it is important to first appreciate how the human eye functions. Our eyes are able to perceive colours due to the presence of three types of cone cells that are sensitive to red, green and blue (RGB) colours. The different extent of stimulation of these cone cells allows us to see a myriad of colours. For instance, a combined stimulation of red and green cones will give the perception of yellow. Perovskite offers excellent colour performance because it is able to produce spectrally “purer” RGB light that is more specific in stimulating the three cone cells in our eyes. This greater control in cone stimulation allows displays to reproduce a wider range of colours that mimic what our eyes perceive in the real world.

Dr WONG Ying Chieh, a member of the research team, said, “An added advantage is that perovskites are easy to synthesise, potentially facilitating their scale-up and reducing the production cost of displays. The time taken for perovskite precursor chemicals to react and form nanocrystals is typically on the order of 10 seconds.”

“Perovskite materials can be coated and processed in a solution form which is similar to paints, and can potentially be used in large-area displays. Although our materials are useful in enhancing the performance of televisions and mobile devices, my vision is to put them into wall-sized displays in our living or work spaces to create realistic virtual environments with rich and natural colours,” added Prof Tan.

The research team is currently working with display companies to commercialise the perovskite colour-enhancement film, and hopes to see the technology in consumer electronic products within the next 2 to 3 years.