Strategies Toward Efficient Blue Perovskite Light‐Emitting Diodes

Abstract

Substantial progress has been made in blue perovskite light-emitting diodes (PeLEDs). In this review, the strategies for high-performance blue PeLEDs are described, and the main focus is on the optimization of the optical and electrical properties of perovskites. In detail, the fundamental device working principles are first elucidated, followed by a systematical discussion of the key issues for achieving high-quality perovskite nanocrystals (NCs) and quasi-2D perovskites. These involve ligand optimization and metal doping in enhancing the carrier transport and reducing the traps of perovskite NCs, as well as the perovskite phase modulation and defect passivation in improving energy transfer and emission efficiency of quasi-2D perovskites. The strategies for efficient 3D mixed-halide perovskite and lead-free perovskite blue LEDs are then briefly introduced. After that, other strategies, including effective charge transport layer, efficient perovskite emission system, and effective device architecture for high light outcoupling efficiency, are further discussed to boost the blue PeLED performances. Meanwhile, the testing standard of blue PeLED lifetime is suggested to enable the direct comparisons of the device operational stability. Finally, challenges and future directions for blue PeLEDs are addressed.

High-Performance Blue Quasi-2D Perovskite Light-Emitting Diodes via Balanced Carrier Confinement and Transfer

“…In quasi-2D perovskites, the photogenerated carriers are driven from a larger bandgap (i.e., low- n ) phase to a smaller bandgap (i.e., high- n ) phase and, subsequently, recombine in the high- n phase (Fig. 3 a) due to the energy funneling effect [ 46 ]. Therefore, an efficient energy transfer from low- n phase to high- n phase in the quasi-2D perovskite is vital for high emission efficiency.…”

“…Particularly, there is a booming development for the device efficiencies of quasi-2D perovskites taking the advantages of the energy funneling effect assisted fast exciton transfer and recombination, and the facilely solution-processed perovskite fabrication [ 42 – 44 ]. Typically, the component of quasi-2D perovskite consists of inorganic Pb–Br octahedral layer and organic spacer cation, which is generally named as B 2 (APbBr 3 ) n− 1 PbBr 4 , where B is an organic spacer cation (e.g., phenylethylammonium: PEA + ), A is a monovalent cation (e.g., Cs + , formamidinium: FA + ), and n represents the number of Pb–Br octahedral layers [ 45 , 46 ]. As we know, inevitable defects are generated during the crystallization of quasi-2D perovskites due to the ionic character of the hybrid perovskites.…”

“…Quasi-2D perovskites usually contain a mixture of layered perovskites with phase distribution from the low- n to high- n phases [ 45 , 46 ]. This is because that there is a complex mixture of colloids with random size distribution in the precursor solution [ 53 ], which can act as nucleation centers to form 2D perovskites with different layers.…”

“…In quasi-2D perovskites, the efficient energy transfer from the larger bandgap phase (i.e., lower- n ) to the smaller bandgap phase (i.e., higher- n ) is essential to realize the high emission efficiency [ 37 , 52 , 54 ]. Specially, different from the green-emissive quasi-2D perovskites, more organic spacer cations are needed to narrow the potential well of Pb–Br octahedral layers for blue emission [ 46 , 55 ]. In other words, there are massive components of organic spacer cations in blue-emissive quasi-2D perovskites, which are harmful to the carrier transfer due to the insulating nature of the organic spacer cations [ 34 , 55 ].…”

Spectral Stable Blue-Light-Emitting Diodes via Asymmetric Organic Diamine Based Dion–Jacobson Perovskites

“… 17 − 20 However, the efficiency for blue PeLEDs is still substantially inferior as compared with other PeLEDs because of the halide segregation issue in the perovskite emitter films. 21 , 22 High-quality blue emitter layers are a prerequisite to the pursuit of high-efficiency blue PeLEDs. Generally, tailoring the three-dimensional (3D) bromide/chloride (Br/Cl) composition is a straightforward strategy for blue emitter perovskite layers.…”