According to foreign media reports, the researchers' newly developed lithium-titanium-based semiconductor-based LEDs have set a new efficiency record that rivals the best organic LEDs (OLEDs).
Compared to OLEDs widely used in high-end consumer electronics, perovskite-based LEDs developed by researchers at Cambridge University are cheaper to manufacture and can be tuned to emit light through near-infrared spectroscopy with visible light and higher color purity.
The researchers' research and design of the perovskite layer in the above-mentioned LEDs achieved nearly 100% internal luminous efficiency, opening up future applications in displays, lighting and communications, and next-generation solar cells.
These perovskite materials, like those used to make high-efficiency solar cells, will one day replace commercial silicon solar cells. Although perovskite-based LEDs have been developed, they are not as effective as conventional OLEDs in converting electrical energy into light.
Hybrid perovskite LEDs, developed four years ago by a team led by Professor Richard Friend of the Cavendish Laboratory at Cambridge University, are promising, but the loss of perovskite layer caused by tiny defects in the crystal structure limits them. Luminous efficiency. Recently, Cambridge researchers and their collaborators from the same group have shown that through the perovskite composite layer formed with the polymer, higher luminous efficiency can be achieved, close to the theoretical efficiency limit of the thin film OLED. Their findings were published in the journal Nature Photonics.
Dr. Dawei Di of the Cavendish Laboratory at Cambridge University, one of the paper collaborators, said: "This perovskite-polymer structure effectively eliminates non-luminescence losses, which is the first time based on perovskites. This performance is achieved in the device. With this hybrid structure, we can basically prevent electrons and positive charges from recombining through defects in the perovskite structure."
The perovskite-polymer blend used in the LED device, referred to as a bulk heterostructure, is made from two-dimensional and three-dimensional perovskite components and insulating polymers. When ultrafast lasers impinge on such polymer structures, multiple pairs of energy-carrying charge pairs move from the 2-D region to the 3-D region at a rate of one-hundredth of a second: the early layering used in LEDs The perovskite structure is much faster. Subsequently, the separated charges in the 3-D region recombine and emit very intense light.
Di said: "Because the energy transfer from the 2-D region to the 3-D region occurs so fast, and the charge in the 3-D region is isolated from the defects of the polymer, these mechanisms can produce defects, thereby effectively preventing energy. loss."
According to Baodan Zhao, the first author of the paper, “The optimal external quantum efficiency of these devices is higher than 20% at current densities associated with display applications, creating a new record for perovskite LEDs, and also on the market today. The best OLEDs have similar efficiency values."
Although such perovskite-based LEDs are comparable in efficiency to OLEDs, they still require better stability if they are to be widely used in consumer electronics. The first developed perovskite LEDs have a lifespan of only a few seconds. The LEDs developed through current research have a half-life of nearly 50 hours, which is a huge advancement in the improvement achieved in just four years, but still does not reach the life expectancy of commercial applications, and therefore will require extensive industrial development planning. . Di pointed out: "Understanding the degradation mechanism of this LED is a key to continuous improvement in the future."
