The research group led by Prof. XIAO Zhengguo from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences prepared large-area and efficient sky-blue perovskite light-emitting diodes (PeLEDs) by blade-coating supersaturated perovskite solution. This work was published in Advanced Materials.

Metal halide PeLEDs can achieve high luminance at low voltage due to their high electrical conductivity, making them ideal for the next generation of energy-saving lighting. The external quantum efficiency (EQE) of red/infrared and green PeLEDs is high at present. Blue/sky-blue PeLEDs are essential for white lighting, while the EQE of blue light is relatively low. This is because the crystallization process of blue/sky-blue perovskite film is difficult to control, which results in poor film quality. Till now, there are no reports on the formation of large-area blue/sky-blue PeLEDs.

Researchers in this work adjusted the composition of perovskite into CsPb(Br_0.84Cl_0.16)₃ based on their previous robust perovskite blade-coating technique for red PeLEDs. They added additional halide amine additives to limit the growth of perovskite grains and passivate the traps, to achieve the sky-blue emission.

Meanwhile, they partially replaced dimethyl sulfoxide (DMSO) with dimethylformamide (DMF) to obtain a more volatile and supersaturated perovskite precursor solution. Perovskite crystal nucleus will precipitate directly from inside of the supersaturated solution in the process of blade-coating, which can effectively increase the density of the nucleus and accelerate the process of nucleation, crystallization, and film-forming, to prepare uniform perovskite films with small grains.

The EQE for blue/sky-blue PeLEDs, prepared by the blade-coating method, reached 10.3%, and the luminescence uniformity and brightness in an area of 28cm² of the PeLEDs are both very good.

This work represents an important step to the commercial application of PeLED lighting.

An ultra large-area sky-blue PeLED (Image by CHU Shenglong et.al)