Beneath the touchscreen of a modern smartphone lies layer upon layer of glass, polarizers, color filters, capacitive touch sensors, and more. Now, researchers have developed a potential all-in-one replacement: photosensitive pixels. These pixels can do much more than just display screens; they can also image objects placed on them, detect fingerprints, and even charge the device.
Perovskites are a popular class of materials in the photovoltaic field. Researchers have discovered that they can be used to create highly efficient solar cells and brighter, better-performing quantum dots. The latest advances show that perovskite LED (PeLED) technology is making significant breakthroughs. For example, a research team at the University of Science and Technology of China, using a novel “weak spatial confinement” method, has successfully increased the brightness of perovskite LEDs to over 1.16 million nits, with a theoretical lifespan exceeding 180,000 hours and a luminous efficiency exceeding 22%, on par with commercial display products.
Researchers hope to enable perovskite devices to both emit light and react to light. The developed perovskite LED material (PeLED) is capable of displaying images under high brightness conditions. The researchers demonstrated red, green, and blue PeLEDs, with a reported brightness of up to 4700 candelas per square meter (compared to the peak brightness of most smartphone displays, which is a few hundred candelas). Furthermore, PeLEDs can efficiently detect light, a property that researchers exploited to create touch screens. Engineering implementation of this dual-function requires sophisticated device structure design and optimized material ratios.
To achieve excellent photoresponsiveness, you need to generate electron carriers within the material. “In perovskites, this is easily achieved.” A carrier transport layer allows electron mobility, which in turn makes it possible to detect touch input. PeLEDs are light-sensitive, making it possible to image objects on a touchscreen display. Research at Cambridge University’s Cavendish Laboratory has shown that perovskite materials have significantly higher carrier mobility than traditional organic materials, providing a theoretical basis for their dual functionality.
The result is a display that combines multiple sensor functions. It can image small, high-contrast objects placed on the display, which should make it a viable fingerprint reader (the prototype display is too small for fingerprint testing). The display is also light-sensitive, allowing it to function as a light sensor for data transmission or as a health monitor. This multifunctional integrated engineering will greatly simplify the internal structure of smart devices.
These functions could help smartphones integrate the multiple separate sensors currently required for displays. Recent trends indicate that this multifunctional integration is a key development direction in the consumer electronics sector. A recent report released by the International Electron Devices Meeting (IEDM) indicates that multifunctional integrated display technology will become a core competitive advantage in next-generation smart devices.
The photosensitivity of PeLEDs has the incredible potential to replace many smartphone sensors, and they also have the special advantage of doubling as solar chargers – the first functional demonstration of a perovskite display generating an electrical charge.
“It’s a fundamental concept that good solar cells should be good LEDs. However, practically combining solar cells with LEDs is difficult due to several engineering challenges.” Scientists at the Swiss Federal Institute of Technology in Lausanne (EPFL) published a review article in the journal Nature Materials, noting that the unique advantages of perovskite materials in this field are being increasingly confirmed by research.
The researchers used a prototype display to charge a supercapacitor, which was then used to power the display. When exposed to white LED indoor lighting, the display’s power conversion efficiency was more than double that when exposed to simulated sunlight, which could be beneficial for consumer devices that spend most of their time indoors.
The researchers noted that their display technology is a proof of concept, and further research is needed to scale it up to a size suitable for consumer electronics. Lifespan is also a concern, as current perovskite materials degrade rapidly; the paper reports an “operational lifetime” of just 18.5 hours.
