L-Type Ligand-Assisted Acid-Free Synthesis of CsPbBr₃ Nanocrystals with Near-Unity Photoluminescence Quantum Yield and High Stability

Abstract

X-type ligands, for example, the pair of oleylamine (OAm) and oleic acid (OA), have been widely used to prepare CsPbX3 nanocrystals (NCs). However, the proton exchange between coordinated OAm and OA may induce the detachment of ligands, resulting in poor performance after cleaning or long-time storage. Herein, density functional theory calculations predict that primary amines (L-type ligands) can stabilize a PbBr x -rich surface and yield a trap-free material with fully delocalized valence band maximum and conduction band minimum states, which can significantly improve the photophysical properties and stability of CsPbBr3 NCs. Along this prediction, a room-temperature reprecipitation method using L-type ligands (OAm, n-octylamine, or undecylamine) as the sole capping ligand has been developed to synthesize high-quality CsPbBr3 NCs with near-unity photoluminescence quantum yield and dramatically improved stability against purification and water treatment. The enhancement can be attributed to the strong binding of unprotonated amines to lead atoms and the effective surface passivation provided by the resulted PbBr x -rich surface, which are highly consistent with the theoretical predictions. This work not only offers an approach to synthesize high-quality perovskite NCs but also provides an in-depth understanding of the surface modification of CsPbX3 NCs for practical applications.

Surface Engineering of All‐Inorganic Perovskite Quantum Dots with Quasi Core−Shell Technique for High‐Performance Photodetectors

“…However, the remained surface morphological defects and the presence of bulky alkylamine ligands hampered the carrier mobility, causing the recombination losses of photogenerated carriers, which remains unresolved. [ 31 ] The defects in perovskite is closely related to the trap‐states, and usually they act as the recombination centers. [ 32,33 ]…”

In Situ Ligand Bonding Management of CsPbI3 Perovskite Quantum Dots Enables High‐Performance Photovoltaics and Red Light‐Emitting Diodes

“…Then umber of vacancies or defects generated in the CsPbI 3 QD surface has been reported as aresult of the lower PLQY and lifetime. [40,41] Therefore,bydecreasing the density of surface trap states,w ew ere able to improve the optical properties of the L-PHE treated QDs.…”

Dynamic Passivation in Perovskite Quantum Dots for Specific Ammonia Detection at Room Temperature

“…One pair of lone pair electrons of ammonia coordinates with Pb cations, leading to significantly passivation effect ( Figure a) . The X‐ray photoelectron spectroscopy (XPS) characterization is further performed to reveal the element state (Figure b,c).…”

“…For CsPbBr 3 QDs after ammonia treatment, one more peak at 399.05 eV can be detected, which can be assigned to N from NH 3. In the case of CsPbBr 3 QDs film, the interaction among Pb cations on the surface will decrease after ammonia removed, resulting in dynamic process of ammonia passivation of CsPbBr 3 QDs film. It is clearly concluded that the introduction of ammonia gas significantly enhances the optical performance of the material with structure retained through an ammonia‐lead coordination passivation.…”

“…A number of studies have demonstrated that the surface defects, originated from excess lead atoms by conventional two‐precursor synthesis, may perform as the media of nonradiative recombination, leading to the sharp decrease of photoluminescence quantum yield (PLQY) accompanied by appearance of multicomponent excited state photoluminescence of perovskite QDs . Previous studies have demonstrated that the amino group plays an important role in morphology control and surface defects passivation of QDs, in which primary amines are supposed to coordinate with lead atoms through lone pair electrons to improve the optical properties of the corresponding QDs …”