Control over the nucleation and growth of lead-halide perovskite crystals is critical to obtain semiconductor films with high quantum yields in optoelectronic devices. In this report, we use the change in fluorescence brightness to image the transformation of individual lead bromide (PbBr 2 ) nanocrystals to methylammonium lead bromide (CH 3 NH 3 PbBr 3 ) via intercalation of CH 3 NH 3 Br. Analyzing this reaction one nanocrystal at a time reveals information that is masked when the fluorescence intensity is averaged over many particles. Sharp rises in the intensity of single nanocrystals indicate they transform much faster than the time it takes for the ensemble average to transform. While the ensemble reaction rate increases with increasing CH 3 NH 3 Br concentration, the intensity rises for individual nanocrystals are insensitive to the CH 3 NH 3 Br concentration. To explain these observations, we propose a phase-transformation model in which the reconstructive transitions necessary to convert a PbBr 2 nanocrystal into CH 3 NH 3 PbBr 3 initially create a high energy barrier for ion intercalation. A critical point in the transformation occurs when the crystal adopts the perovskite phase, at which point the activation energy for further ion intercalation becomes progressively smaller. Monte Carlo simulations that incorporate this change in activation barrier into the likelihood of reaction events reproduce key experimental observations for the intensity trajectories of individual particles. The insights gained from this study may be used to further control the crystallization of CH 3 NH 3 PbBr 3 and other solution-processed semiconductors.
more »
« less
Structural characterization of N-(4-carboxybenzyl)pyridinium bromide: Hydrogen bonding between bromide and a carboxylic acid
- Award ID(s):
- 1955648
- NSF-PAR ID:
- 10412479
- Date Published:
- Journal Name:
- Journal of Molecular Structure
- Volume:
- 1276
- Issue:
- C
- ISSN:
- 0022-2860
- Page Range / eLocation ID:
- 134727
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Free chlorine and free bromine ( e.g. , HOCl and HOBr) are employed as disinfectants in a variety of aqueous systems, including drinking water, wastewater, ballast water, recreational waters, and cleaning products. Yet, the most widely used methods for quantifying free halogens, including those employing N , N -diethyl- p -phenylenediamine (DPD), cannot distinguish between HOCl and HOBr. Herein, we report methods for selectively quantifying free halogens in a variety of aqueous systems using 1,3,5-trimethoxybenzene (TMB). At near-neutral pH, TMB reacted on the order of seconds with HOCl, HOBr, and inorganic bromamines to yield halogenated products that were readily quantified by liquid chromatography or, following liquid–liquid extraction, gas chromatography-mass spectrometry (GC-MS). The chlorinated and brominated products of TMB were stable, and their molar concentrations were used to calculate the original concentrations of HOCl (method quantitation limit (MQL) by GC-MS = 15 nmol L −1 = 1.1 μg L −1 as Cl 2 ) and HOBr (MQL by GC-MS = 30 nmol L −1 = 2 μg L −1 as Cl 2 ), respectively. Moreover, TMB derivatization was efficacious for quantifying active halogenating agents in drinking water, pool water, chlorinated surface waters, and simulated spa waters treated with 1-bromo-3-chloro-5,5-dimethylhydantoin. TMB was also used to quantify bromide as a trace impurity in 20 nominally bromide-free reagents (following oxidation of bromide by HOCl to HOBr). Several possible interferents were tested, and iodide was identified as impeding accurate quantitation of HOCl and HOBr. Overall, compared to the DPD method, TMB can provide lower MQLs, larger linear ranges, and selectivity between HOCl and HOBr.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.molstruc.2022.134727
