Researchers from Yonsei University, Sungkyunkwan University and Institute for Basic Science (IBS) have proposed a rapid crystallization method based on hot-antisolvent bathing for realization of deep-blue perovskite light-emitting diodes (PeLEDs). The rapid crystallization method manipulates 2D perovskite phase evolution by controlling the crystallization kinetics for the fabrication of phase-pure 2D Ruddlesden‒Popper perovskites (2D-RPPs), enabling deep-blue-emissive perovskite LEDs.
PeLEDs are considered as promising candidates for next-generation solution-processed full-color displays. However, the external quantum efficiencies (EQEs) and operational stabilities of deep-blue (<460 nm) PeLEDs still lag far behind their red and green counterparts. 2D-RPPs have excellent optoelectronic properties—ideal for LEDs. Although 2D-RPP-based LEDs have rapidly progressed in terms of performance, it is still challenging to demonstrate blue-emissive and color-pure LEDs. The deep blue of current LED displays is usually produced by indium gallium nitride (InGaN), a costly substance. In the field of LEDs, researchers are seeking alternatives and one of them could be found in 2D-RPPs.
The researchers explained that when the as-spin-coated precursor wet film was submerged in a hot-bath of diethyl ether, immediate crystallization occurred, due to the rapid extraction of precursor solvent by diethyl ether. Extremely fast crystallization kinetics allowed all the chemical species to be randomly distributed throughout the film, successfully yielding highly phase-pure 2D-RPP crystals.
Conventional fabrication processes for producing 2D-RPP films (e.g., hot-casting and antisolvent dripping) induce spatial segregation of the chemical species during the film crystallization. The resulting mixed perovskite phases evoke the emission from perovskite phase with a smaller bandgap, which hinders deep-blue emissions. A strategy capable of precisely controlling the phase evolution of the 2D-RPPs during crystallization was required to achieve deep-blue LEDs.
Steady-state photoluminescence and ultrafast transient absorption revealed that rapid crystallization via hot-antisolvent bathing enables highly phase-pure 2D perovskite films with randomly oriented crystals. The random orientations of the 2D perovskite crystals enhanced charge transport and improved charge mobility to benefit device performance. The resulting deep-blue-emissive perovskite LEDs exhibited a maximum external quantum efficiency (EQE) of 0.63% with an emission wavelength centered at 437 nm. Prolonged stability of the unencapsulated PeLEDs was further confirmed with negligibly changed EL spectra, highly comparable to those of state-of-the-art devices.
According to senior author Jooho Moon, professor in the Department of Materials Science and Engineering at Yonsei University, "This work provides a novel approach to realize high performance and spectrally stable deep-blue perovskite LEDs. Our research suggests that the control of the crystallization kinetic is the key for the preparation of phase-pure 2D-RPP crystals, exhibiting great promise for addressing current challenges."