Research into perovskite nanocrystals (PNCs) has uncovered interesting properties compared to their bulk counterparts, including tunable optical properties due to size‐dependent quantum confinement effect (QCE). More recently, smaller PNCs with even stronger QCE have been discovered, such as perovskite magic sized clusters (PMSCs) and ligand passivated PbX2metal halide molecular clusters (MHMCs) analogous to perovskites.
This review aims to present recent data comparing and contrasting the optical and structural properties of PQDs, PMSCs, and MHMCs, where CsPbBr3PQDs have first excitonic absorption around 520 nm, the corresponding PMSCS have absorption around 420 nm, and ligand passivated MHMCs absorb around 400 nm.
Compared to normal perovskite quantum dots (PQDs), these clusters exhibit both a much bluer optical absorption and emission and larger surface‐to‐volume (S/V) ratio. Due to their larger S/V ratio, the clusters tend to have more surface defects that require more effective passivation for stability.
Recent study of novel clusters has led to better understanding of their properties. The sharper optical bands of clusters indicate relatively narrow or single size distribution, which, in conjunction with their blue absorption and emission, makes them potentially attractive for applications in fields such as blue single photon emission.
- Award ID(s):
- NSF-PAR ID:
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of the Chinese Chemical Society
- Page Range / eLocation ID:
- p. 1609-1617
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
Recent progress has been made on the synthesis and characterization of metal halide perovskite magic-sized clusters (PMSCs) with ABX 3 composition ( A = C H 3 N H 3 + or Cs + , B = P b 2 + , and X = C l − , Br - , or I - ). However, their mechanism of growth and structure is still not well understood. In our effort to understand their structure and growth, we discovered that a new species can be formed without the CH 3 NH 3 + component, which we name as molecular clusters (MCs). Specifically, CH 3 NH 3 PbBr 3 PMSCs, with a characteristic absorption peak at 424 nm, are synthesized using PbBr 2 and CH 3 NH 3 Br as precursors and butylamine (BTYA) and valeric acid (VA) as ligands, while MCs, with an absorption peak at 402 nm, are synthesized using solely PbBr 2 and BTYA, without CH 3 NH 3 Br. Interestingly, PMSCs are converted spontaneously overtime into MCs. An isosbestic point in their electronic absorption spectra indicates a direct interplay between the PMSCs and MCs. Therefore, we suggest that the MCs are precursors to the PMSCs. From spectroscopic and extended X-ray absorption fine structure (EXAFS) results, we propose some tentative structural models for the MCs. The discovery of the MCs is critical to understanding the growth of PMSCs as well as larger perovskite quantum dots (PQDs) or nanocrystals (PNCs).more » « less
The surface of CH3NH3PbBr3perovskite nanocrystals (PNCs) plays a critical role in determining their optical properties and stability. The introduction of capping ligands can enhance photoluminescence (PL), reduce non‐radiative recombination, and improve stability. Here, we report a facile synthesis of CH3NH3PbBr3PNCs with strong and highly stable green PL using melamine (Mela) as a simple and low‐cost capping ligand. The resulting CH3NH3PbBr3/Mela PNCs have cubic phase crystal structure with an average particle size of 5.29±0.06 nm. The optical absorption and PL of the CH3NH3PbBr3/Mela PNCs with narrow bandwidth can be tuned within the visible region, and the PL quantum yield (QY) reached 52.3% compared to 0.4% the pristine CH3NH3PbBr3PNCs. A synergistic effect between NH3+and the electron‐rich nitrogen atoms together with p‐p stacking capacity, likely contributes to enhance the PL by effectively passivating of the trap states of PNCs. Furthermore, melamine‐capped PNCs show high stability in protic solvents as a result of the steric bulkiness of the triazine rings, owing to the planar structure together with hydrogen bonding of melamine, which prevents solvent molecules from reaching and reacting with the core of PNCs. This study demonstrates a simple and effective approach for stabilizing PNCs for potential applications such as solar cells and LEDs.
As a class of semiconductor nanocrystals that exhibit high photoluminescence quantum yield (PLQY) at tunable wavelengths, perovskite nanocrystals (PNCs) are attractive candidates for optoelectronic and light‐emitting devices. However, attempts to optimize PNC integration into such applications suffer from PNC instability and loss of PL over time. Here, we describe the impact of organic and polymeric N‐oxides when used in conjunction with PNCs, whereby a significant increase in PNC quantum yield is observed in solution, and stable PL emission is obtained in polymeric nanocomposites. Specifically, when using aliphatic N‐oxides in ligand exchange with CsPbBr3PNCs in solution, a substantial boost in PNC brightness is observed (~40% or more PLQY increase), followed by an alteration of the perovskite chemistry. When N‐oxide substituents are positioned pendent to a poly(n‐butyl methacrylate) backbone, the optically clear flexible nanocomposite films obtained have bright PL emission and maintain optical clarity for months. X‐ray diffraction is useful for characterizing the PNC crystalline structure following exposure to aliphatic N‐oxides, while electron microscopy (EM) and small‐angle X‐ray scattering (SAXS) measurements of the PNC‐polymer nanocomposites show this polymeric N‐oxide platform to cleanly disperse PNCs in flexible polymer films.
A few unit cells of thick colloidal CsPbBr3nanoplatelets (NPLs) exhibit strong quantum confinement. However, due to the increased surface‐to‐volume ratio, they show poor photoluminescence quantum yield (PLQY) resulting from surface traps. Here, a unique, quantum‐confined core/crown perovskite is reported for the first time, where the CsPbBr3NPL surface is passivated by laterally grown thin FAPbBr3crown layers. Unlike regular core/shells, the FAPbBr3is coated around the core NPLs resulting in blue emission. Careful control of the growth kinetics while monitoring growth using in situ PL led to the formation of core/crown perovskites with nearly two times improvement in thin film PLQYs. HR‐TEM analyses show that the interplanar distances of the core match with CsPbBr3and the crown match with FAPbBr3. The XRD and TEM analyses revealed that their thickness remains the same even if Cs+to FA+ratios are varied, indicating lateral growth of FAPbBr3around the CsPbBr3core. Further, FA+ions in the crown lattice are confirmed by FTIR and1HNMR. Finally, considering their high PLQYs and narrow linewidths, the core/crown NPLs are employed as blue emitters in light‐emitting diodes, and a maximum external quantum efficiency of 0.4% at 2.71 eV (457 nm) with a luminance of 513 cd m−2is achieved.
Instability of colloidal iodine‐based inorganic perovskite CsPbX3(X = Cl, Br, I) nanocrystals (IPNCs) represents a major obstacle in lead‐halide IPNC research and application. Herein, a ligand‐anchoring process is reported that enables significantly improved colloidal stability of the iodine‐based IPNCs for over 10 months in ambient. Apart from the previous efforts in searching for strong binding ligands to cap the IPNCs to incrementally reduce the exposure of the IPNC surface to the harsh colloidal environment, the ligand‐anchoring method demonstrates that such an exposure can be reduced substantially by suppressing the dynamic ligand exchange around the colloidal IPNCs. In the IPNC synthesis solution with common oleic acid (OA) and oleylamine (OLA) ligands with relative weak binding to IPNCs, a systematic reduction of the ligand concentration using hexane by an order of magnitude has shown to be effective in achieving OA/OLA ligand‐anchored iodine‐based IPNCs with superior stability as confirmed in optical absorption, photoluminescence,1H solution nuclear magnetic resonance spectroscopy, and photoresponse. This result has revealed that the intermittent exposure of the IPNC surface during the dynamic ligand exchange is a primary mechanism underlying the colloidal IPNC instability, which can be resolved in the ligand‐anchoring process by suppressing such dynamic activities.