Bandgap tuning by mixing halide anions is one of the most attractive properties of metal halide perovskites. However, mixed halide perovskites usually undergo phase separation under bias. Here, researchers from Linköping University in Sweden obtained a high-performance and color-stable blue perovskite LED based on a mixed bromine/chlorine three-dimensional structure. It is proved that the color instability of CsPb(Br1 xClx)3 is caused by the surface defects of the perovskite grain boundary. Through effective defect passivation, blue electroluminescence Peled with stable color is obtained.
The author's work provides new insights into the color instability of mixed halide perovskites and can promote the new development of high-performance and color-stable blue perovskites. The related paper was published in the Journal of Physical Chemistry Letters with the title "Color-Stable Blue Light-Emitting Diodes Enabled by Effective Passivation of Mixed Halide Perovskites".
Perovskite-type light-emitting diodes (LEDs) have become solutions due to their excellent optical and electrical properties, including high photoluminescence quantum yield (PLQY), narrow emission bandwidth, tunable bandgap, and high charge carrier mobility. A promising candidate for processing display and lighting applications. In the past few years, considerable progress has been made in this area. The most advanced green, red and near-infrared PELEDs have achieved high external quantum efficiency (EQE) of more than 20%. Despite these advances, one of the remaining challenges is to develop deep blue perovskite devices with excellent performance.
One approach to blue perovskites is to develop quantum confined structures based on pure bromine perovskites; for example, hybrid perovskites (a mixture of 2D/quasi-2D/3D phases) and perovskite quantum dots have been developed (QD). These quantum confined structures contain long-chain organic ligands to inhibit the growth of perovskite crystals, keeping at least one direction of the crystals within the Bohr diameter range to increase the bandgap. However, it is quite difficult to achieve uniform quantum confinement; for example, the presence of multiple phases in mixed-dimensional perovskites sometimes even leads to broad emission and limits color purity.
In addition, due to the insulating properties of long-chain organic ligands, these quantum confined structures often suffer from poor charge injection, so the resulting devices have lower brightness. Another way to develop blue perovskite devices is to use mixed Br/Cl perovskite. Although continuously adjustable emission colors with different halide ions are one of the most attractive features of perovskites, this mixed halide strategy is usually limited by color instability. Most previous reports on mixed Br/Cl-based blue perovskites show that the color will continue to change during operation, usually due to halide ion migration. Recently, it has been proven that by introducing cationic surfactants into the precursor solution or using steam-assisted crystallization technology in the film crystallization process to homogenize the halide composition, spectral shifts can be suppressed, and the device performance can be greatly improved.
