Complementary Triple-Ligand Engineering Approach to Methylamine Lead Bromide Nanocrystals for High-Performance Light-Emitting Diodes

Abstract

Conjugated and short-molecule capping ligands have been demonstrated as a valid strategy for achieving high-efficiency perovskite nanocrystal (NCs) light-emitting diodes (LEDs) owing to their advantage of allowing efficient carrier transport between NCs. However, monotonously utilizing conjugated ligands cannot achieve sufficient surface modification/passivation for perovskite NCs, leading to their poor photoluminescence quantum yield (PLQY) and dispersibility. This work designs a complementary ligand synthesis method to obtain high-quality methylamine lead bromide (MAPbBr 3 ) NCs and then leverage them into efficient LEDs. The complementary ligand system combines a conjugated ligand 3-phenyl-2-propen-1-amine (PPA) and a long-chain ligand didodecyldimethylammonium bromide (DDAB) together with a well-known inductive inorganic ligand ZnBr 2 . With such complementary ligand engineering, we significantly improve the emissive features of MAPbBr 3 NCs (PLQY: 99% ± 0.7%). Simultaneously, the complementary ligand strategy facilitated the adequate charge transportation in related NCs films and modified the interfacial energy-level alignment when the NCs assemble as an emitting layer into LEDs. Finally, based on this NCs synthesis method, highefficiency green LEDs were achieved, exhibiting the maximum luminance of 1.59 × 10 4 cd m −2 , a current efficiency of 23.7 cd A −1 , and an external quantum efficiency of 7.8%. Our finding could provide a new avenue for further development of LEDs and their commercial application.

Surface Reconstruction of CsPbBr3 Nanocrystals by the Ligand Engineering Approach for Achieving High Quantum Yield and Improved Stability

“…Both samples show cube-shaped morphologies, but the surface-cured CsPbBr 3 NCs present a more clearer crystal boundary because of the steric hindrance between the ligands, which is indicative of the better crystalline quality (Figure 2a,c). 38,39 The results are also further confirmed by the XRD pattern (Figure S4). All samples possess the identical characteristic patterns, corresponding to orthorhombic-phase perovskite (18-0364).…”

“…TEM images are collected to reflect the effect of surface treatment on crystal shape, size, and structure. Both samples show cube-shaped morphologies, but the surface-cured CsPbBr 3 NCs present a more clearer crystal boundary because of the steric hindrance between the ligands, which is indicative of the better crystalline quality (Figure a,c). , The results are also further confirmed by the XRD pattern (Figure S4). All samples possess the identical characteristic patterns, corresponding to orthorhombic-phase perovskite (18-0364). , Besides, the increase in the peak intensity of planes after the surface engineering is observed, which verifies the improved crystallinity again.…”

“…Didodecyl dimethylammonium bromide (DDAB) with completely substituted quaternary amines is permanently charged fully, which prevents the absence of the acid–base reactions . They have been widely used for the improvement of the stability and luminescence enhancement. − In addition, postsynthetic treatments with metal halide salts, such as PbBr 2 and ZnBr 2 , are also effective in manipulation of the defects and PL maximization, , whereas this strategy needs a polar solvent or high temperature to dissolve metal halide salts. It can compromise structural stability owing to the ionic characters inherently or increase experiment complexity. , A few reports demonstrate that the hybrid ligand can enhance emissive properties as well as colloidal stability.…”

Ligands in Lead Halide Perovskite Nanocrystals: From Synthesis to Optoelectronic Applications

“…Zhao et al prepared the MAPbBr 3 NCs capped by triple-ligands, including 3-phenyl-2-propen-1-amine (PPA) DDAB and ZnBr 2 . [151] Due to the passivation of surface traps, the NCs showed near-unity of PLQY value. By varying the ratio of ligands, the energy level of the MAPbBr 3 NCs film could be adjusted, thus promoting charge injection and transport of the device which could reach a maximum luminance of 15 900 cd m −2 with EQE of 7.8% (Figure 15d).…”

In Situ Tetraalkylammonium Ligand Engineering of Organic–Inorganic Hybrid Perovskite Nanoparticles for Enhancing Long-Term Stability and Optical Tunability

“…This failure primarily occurs because of the insulating nature of organic compounds; lengthy alkyl ligands hinder electronic carrier transport, whereas short ligands provide unsatisfactory stability. , Moreover, ligand binding is a highly dynamic process wherein ligands can be easily detached from the NP surfaces. Therefore, the ligand concentration in the reaction mixture should be intentionally optimized to achieve the desired properties, such as high PL and long-term stability. , In contrast to the conventional monoalkylamines, TAA ligands have emerged as efficient passivation ligands owing to their innate and prominent cationic nature and the consequently enhanced electrostatic attraction-based binding on the OIHP NPs. ,− However, TAA-based passivation necessitates an additional post-synthetic ligand-exchange procedure, which could significantly inhibit the facile and reproducible synthesis of stable OIHP NPs. Therefore, the development of in situ ligand engineering where the OIHP NPs are ligand-engineered at the moment of synthesis would be a substantial advance in this field.…”