Engineering Colloidal Perovskite Nanocrystals and Devices for Efficient and Large-Area Light-Emitting Diodes

Abstract

Metrics & MoreArticle Recommendations * sı Supporting Information CONSPECTUS: Colloidal metal halide perovskite nanocrystals (PNCs) have high color purity, solution processability, high luminescence efficiency, and facile color tunability in visible wavelengths and therefore show promise as light emitters in next-generation displays. The external quantum efficiency (EQE) of PNC lightemitting diodes (LEDs) has been rapidly increased to reach 24.96% by using colloidal PNCs and 28.9% using on-substrate in situ synthesized PNCs. However, high operating stability and a further increase of EQE in PNC-LEDs have been impeded for three reasons: (1) Colloidal PNCs consist of ionic crystal structures in which ligands bind dynamically and therefore easily agglomerate in colloidal solution and films;(2) Long-alkyl-chain organic ligands that adhere to the PNC surface improve the photoluminescence quantum efficiency and colloidal stability of PNCs in solution but impede charge transport in PNC films and limit their electroluminescence efficiency in LEDs;(3) Unoptimized device structure and nonuniform PNC films limit the charge balance and reduce the device efficiency in PNC-LEDs.In this Account, we summarize strategies to solve the limitations in PNCs and PNC-LEDs as consequences of photoluminescence quantum efficiency in PNCs and the charge-balance factor and out-coupling factor in LEDs, which together determine the EQE of PNC-LEDs. We introduce the fundamental photophysical properties of colloidal PNCs related to effective mass of charge carriers and surface stoichiometry, requirements for PNC surface stabilization, and subsequent research strategies to demonstrate highly efficient colloidal PNCs and PNC-LEDs with high operating stability. First, we present various ligand-engineering strategies that have been used to achieve both efficient carrier injection and radiative recombination in PNC films. In situ ligand engineering reduces ligand length and concentration during synthesis of colloidal PNCs, and it can achieve size-independent high color purity and high luminescent efficiency in PNCs. Postsynthesis ligand engineering such as optimized purification, replacement of organic ligands with inorganic ligands or strongly bound ligands can increase charge transport and coupling between PNC dots in films. The luminescence efficiency of PNCs and PNC-LEDs can be further increased by various postsynthesis ligand-engineering methods or by sequential treatment with different ligands. Second, we present methods to modify the crystal structure in PNCs to have alloy-or core/shell-like structure. Such crystal engineering is performed by the correlation between entropy and enthalpy in PNCs and result in increased carrier confinement (increased radiative recombination) and reduced defects (decreased nonradiative recombination). Third, we present strategies to boost the charge-balance factor and out-coupling factor in PNC-LEDs such as modification of thickness of each layer and insertion of additional interlayers, and outcoupling hemispher...

Achieving a near-unity photoluminescence quantum yield and high stability of CsPbI3 nanoplatelets by hydroiodic acid-assisted ligand treatment

“…After the addition of HI, the intensity of the –NH 3 + signal significantly decreases, 49 and another signal peak appears at 401.1 eV, indicating the removal of OA and the formation of a non-protonated amine (NH 2 ). The treated NPLs with surface ligand modification show a substantial enhancement of the NH 2 signal at 401.1 eV, 51,52 associated with the non-protonated amine of DDDAm. The binding energy of Cs 3d shows no significant changes after HI in situ etching and DDDAm treatment (Fig.…”

Metal Halide Perovskites: Promising Materials for Light-Emitting Diodes

“…Despite the promising potential of PeQDs in LED applications, the highly dynamic adsorption and desorption of surface ligands for PeQDs will influence their stability and PLQY during the process of purification, film formation and long-term storage [115]. In addition, ligands with long alkyl chains, such as the commonly used oleic acid (OA) and oleylamine (OAm), have lower conductibility and poor interaction between PeQDs [116]. These shortages limit the practical applications of PeQD LEDs.…”

Potential and perspectives of halide perovskites in light emitting devices

“…As a result, various strategies for post-synthesis surface modification of perovskite nanocrystals have been developed, for instance, ligand attachment for surface stabilization or anion exchange to passivate surface defects. The main research aspects of colloidal routes to PeLEDs can be separated into three major areas: (1) crystal growth and size control, (2) surface stabilization and ligand engineering, (3) perovskite integration and device engineering [ 91 ].…”