Sweden: Energy-Efficient Lighting The Future is Blue: How Light-Emitting Diodes Can Drastically Reduce Energy Consumption
Researchers at Linköping University, Sweden, have developed efficient blue light-emitting diodes based on halide perovskites. The new LEDs may open the way to cheap and energy-efficient illumination.
Linköping/Sweden — Illumination is responsible for approximately 20 % of global electricity consumption, a figure that could be reduced to 5 % if all light sources consisted of light-emitting diodes (LEDs). The blue-white LEDs currently in use, however, need complicated manufacturing methods and are expensive, which makes it more difficult to achieve a global transition.
LEDs manufactured from halide perovskites could be a cheaper and more eco-friendly alternative for both illumination and LED-based monitors. Perovskites are a family of semiconducting materials defined by their cubic crystal structure. They have good light-emitting properties and are easy to manufacture. Using elements from the halogen group, i.e. fluorine, chlorine, bromine and iodine, perovskites can be given properties that depend on the chemical composition of the crystal.
LEDs for green and red light have already been created with perovskites, but one colour, blue, has so far been lacking, making it impossible to achieve white light. “Blue light is the key to bringing light-emitting perovskites to practical applications. Our most recent breakthrough is one step on the way”, says Feng Gao, professor at the Department of Physics, Chemistry and Biology at Linköping University.
Feng Gao’s research group, in collaboration with colleagues in Lund, Great Britain, Germany, China and Denmark, has managed to create halide perovskites that give stable emission in the wavelength range 451-490 nanometres — corresponding to deep blue to sky blue colours. Max Karlsson is doctoral student at Linköping University and joint first author of the article now published in Nature Communications. He argues that metal-halide perovskites are easily colour-tuneable over the whole visible spectrum by simple alloying. However, they also exhibit demixing and a blue LED turns green during operation. The scientists have found a method that can prevent this colour shift by controlling the film crystallisation dynamics when creating the perovskite. These findings could pave the way for stable perovskite alloys, not only for LEDs but also for solar cells.
The challenge of creating blue light in perovskites is that it requires a chemical composition with a large fraction of chloride, which makes the perovskite unstable. Blue perovskite-based LEDs have previously been created with using what is known as the “quantum confinement technique”, which gives low-intensity LEDs with poor efficiency. However, stable perovskites with the desired amount of chloride can be created with the aid of the “vapour-assisted crystallisation technique”. Furthermore, the Linköping University researchers have achieved an energy efficiency of up to 11 % for the blue perovskite-based LEDs.
The researchers are convinced that they are able to show that blue light-emitting diodes based on halide perovskites can be both efficient and stable across a broad spectrum, without using quantum confinement. In this case, they would have managed to create one of the most efficient blue perovskite-based LEDs so far known.
The science of perovskites is a relatively new research field that has aroused major international interest, since it offers a great potential for developing cheap and efficient materials. Feng Gao, however, is quick to point out that the work they have done is basic research, and applications are still some way off in future.
References: Mixed Halide Perovskites for Spectrally Stable and High-Efficiency Blue Light-Emitting Diodes; Max Karlsson, Ziyue Yi, Sebastian Reichert, Xiyu Luo, Weihua Lin, Zeyu Zhang, Chunxiong Bao, Rui Zhang, Sai Bai, Guanhaojie Zheng, Pengpeng Teng, Lian Duan, Yue Lu, Kaibo Zheng, Tönu Pullerits, Carsten Deibel, Weidong Xu, Richard Friend, and Feng Gao. Nature Communications 2021. DOI: 10.1038/s41467-020-20582-6