An official website of the United States government
We have synthesized inherently chiral cesium lead halide perovskite magic-sized clusters (PMSCs) and ligand-assisted metal halide molecular clusters (MHMCs) using the achiral ligands octanoic acid (OCA) and octylamine (OCAm). UV–vis electronic absorption was used to confirm characteristic absorption bands while circular dichroism (CD) spectroscopy was utilized to determine their chiroptical activity in the 412–419 and 395–405 nm regions, respectively. In contrast, the larger sized counterpart of PMSCs, namely, perovskite quantum dots (PQDs), do not show chirality. The inherent chirality of the clusters is tentatively attributed to a twisted chiral layered structure, defect-induced chiral structure, or twisted Pb–Br octahedra
more »
« less
Distinguishing metal halide molecular clusters from perovskite magic sized clusters in the synthesis of metal halide perovskite nanostructures
Abstract BackgroundResearch 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. ObjectiveThis 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. ResultsCompared 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. ConclusionRecent 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.
more »
« less
- Award ID(s):
- 2203633
- PAR ID:
- 10441426
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of the Chinese Chemical Society
- Volume:
- 70
- Issue:
- 8
- ISSN:
- 0009-4536
- Page Range / eLocation ID:
- p. 1609-1617
- Format(s):
- 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
-
Mn2+doping of CsPbBr3perovskite magic‐sized clusters (PMSCs) has been reported previously, where PMSCs with first excitonic absorption and photoluminescence (PL) around 425 nm were reported originally, followed by Mn2+‐doped PMSCs with host absorption and PL around 400 nm. There, the observed 25 nm blueshift was attributed to smaller PMSCs or the Cl−ions introduced by MnCl2as dopant precursor. However, subsequent studies suggest that the 400 nm band may instead be due to ligand‐assisted metal halide molecular clusters (MHMCs), which lack the A component of perovskite. This raises the question whether the originally claimed Mn2+‐doped PMSCs are actually MHMCs. To unambiguously address this issue, Mn2+‐doped CH3NH3PbBr3PMSCs were synthesized with PL at both 440 nm, attributed to the PMSC, and at 600 nm, attributed to Mn2+. Blueshifting of the host absorption and PL bands due to Cl−codoping is avoided by selecting MnBr2as dopant precursor rather than MnCl2. Dopant incorporation into PMSCs is further supported by PL excitation, time‐resolved PL, and electron paramagnetic resonance studies. This work provides direct and strong evidence of successful Mn2+doping in PMSCs.more » « less
-
Ligand‐assisted perovskite nanoclusters (PNCs) have been synthesized using oleylamine and L‐ or D‐cysteine as confirmed based on their characteristic electronic absorption bands around 430 nm based on ultraviolet‐visible spectra. Circular dichroism (CD) spectra show distinct chiroptical bands in the 430–440 nm region, revealing the chirality of the PNCs. Interestingly, the sign of the CD signal is always negative, independent of the chirality for L‐ or D‐cystine. This 430–440 nm CD band is tentatively attributed to the formation of new chiral stereocenters within the PNCs with an uneven ratio of two enantiomers induced by the asymmetric liquid–liquid interface from the solvent and antisolvent used during synthesis.more » « less
-
The excited state dynamics of ligand-passivated PbBr2 molecular clusters (MCs) in solution have been investigated for the first time using femtosecond transient absorption spectroscopy. The results uncover a transient bleach (TB) feature peaked around 404 nm, matching the ground state electronic absorption band peaked at 404 nm. The TB recovery signal can be fitted with a triple exponential with fast (10 ps), medium (350 ps), and long (1.8 ns) time constants. The medium and long time constants are very similar to those observed in the timeresolved photoluminescence (TRPL) decay monitored at 412 nm. The TB fast component is attributed to vibrational relaxation in the excited electronic state while the medium component with dominant amplitude is attributed to recombination between the relaxed electron and hole. The small amplitude slow component is assigned to electrons in a relatively long-lived excited electronic state, e.g., triplet state, or shallow trap state due to defects. This study provides new insights into the excited state dynamics of metal halide MCs.more » « less
