Blue perovskite light-emitting diodes: Opportunities and challenges

Abstract

Metal halide perovskites are considered as promising candidates for lighting applications owing to their excellent optoelectronic properties, such as high electron/hole mobility, high photoluminescence quantum yield, high color purity, and facile color tunability. In recent years, perovskite light-emitting diodes (LEDs) have developed rapidly, and their external quantum efficiencies (EQEs) have exceeded 20% for green and red emissions. However, the EQEs and stabilities of blue (particularly deep-blue) perovskite LEDs are still inferior to the green and red counterparts, which severely restricts the application of perovskite LEDs in high-performance and wide color gamut displays as well as white light illumination. Therefore, summarizing the development of blue perovskite LEDs and discussing the opportunities and challenges associated with their future applications will help to guide the further development of the entire perovskite LED field. In this review, according to the emission color, we divide the blue perovskite LEDs into three parts for a better discussion, i.e., the emissions in the sky-blue, pure-blue, and deep-blue regions. We introduce their developed history and discuss the basic strategies to achieve blue emission. There are three typical methods to obtain perovskite emitters with blue emission, i.e., (1) composition engineering, (2) dimensional engineering, and (3) synthesis of perovskite nanocrystals and quantum dots. For composition engineering, changing ions in perovskite ABX3 structure can easily tune the perovskite emission color, particularly while changing the anions in “X” position. Therefore, modulating the ratio between the X-site anions of Br− and Cl− can cause perovskites to emit blue photons ranging from 420 to 490 nm, which almost covers the entire blue spectrum. For dimensional engineering, perovskite materials can form a series of low-dimensional structures (layered structures) with the insertion of organic ligands between the perovskite frameworks. This type of low-dimensional perovskite material typically exhibits better lighting properties than those exhibited by its three-dimensional counterpart owing to its unique charge or energy transfer process of charge carriers. Blue perovskite nanocrystals and quantum dots with high photoluminescence quantum yields are excellent candidates for realizing high-performance pure-blue and deep-blue devices because they can easily incorporate Cl− in their crystals, which is considerably limited in perovskite thin films owing to the poor solubility of inorganic chloride sources in polar solvents. Furthermore, we discuss several challenges associated with blue perovskite LEDs, such as the inferior device performance in the pure-blue and deep-blue regions, difficulty in hole injection, electroluminescence (EL) instability of mixed halide perovskite systems, and lagged operation lifetime, and introduce potential solutions accordingly. Note that the challenges faced by blue perovskite LEDs are also the opportunities for research in this area. Therefore, this review is of a great reference value for the next evolution of blue perovskite LEDs.