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).
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Doping and ion substitution in colloidal metal halide perovskite nanocrystals
The past decade has witnessed tremendous advances in synthesis of metal halide perovskites and their use for a rich variety of optoelectronics applications. Metal halide perovskite has the general formula ABX 3 , where A is a monovalent cation (which can be either organic ( e.g. , CH 3 NH 3 + (MA), CH(NH 2 ) 2 + (FA)) or inorganic ( e.g. , Cs + )), B is a divalent metal cation (usually Pb 2+ ), and X is a halogen anion (Cl − , Br − , I − ). Particularly, the photoluminescence (PL) properties of metal halide perovskites have garnered much attention due to the recent rapid development of perovskite nanocrystals. The introduction of capping ligands enables the synthesis of colloidal perovskite nanocrystals which offer new insight into dimension-dependent physical properties compared to their bulk counterparts. It is notable that doping and ion substitution represent effective strategies for tailoring the optoelectronic properties ( e.g. , absorption band gap, PL emission, and quantum yield (QY)) and stabilities of perovskite nanocrystals. The doping and ion substitution processes can be performed during or after the synthesis of colloidal nanocrystals by incorporating new A′, B′, or X′ site ions into the A, B, or X sites of ABX 3 perovskites. Interestingly, both isovalent and heterovalent doping and ion substitution can be conducted on colloidal perovskite nanocrystals. In this review, the general background of perovskite nanocrystals synthesis is first introduced. The effects of A-site, B-site, and X-site ionic doping and substitution on the optoelectronic properties and stabilities of colloidal metal halide perovskite nanocrystals are then detailed. Finally, possible applications and future research directions of doped and ion-substituted colloidal perovskite nanocrystals are also discussed.
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- Award ID(s):
- 1914713
- PAR ID:
- 10226170
- Date Published:
- Journal Name:
- Chemical Society Reviews
- Volume:
- 49
- Issue:
- 14
- ISSN:
- 0306-0012
- Page Range / eLocation ID:
- 4953 to 5007
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Lead halide perovskite (LHP) nanocrystals (NCs) are considered an emerging class of advanced functional materials with numerous outstanding optoelectronic characteristics. Despite their success in the field, their precision synthesis and fundamental mechanistic studies remain a challenge. The vast colloidal synthesis and processing parameters of LHP NCs in combination with the batch‐to‐batch and lab‐to‐lab variation problems further complicate their progress. In response, a self‐driving fluidic micro‐processor is presented for accelerated navigation through the complex synthesis and processing parameter space of NCs with multistage chemistries. The capability of the developed autonomous experimentation strategy is demonstrated for a time‐, material‐, and labor‐efficient search through the sequential halide exchange and cation doping reactions of LHP NCs. Next, a machine learning model of the modular fluidic micro‐processors is autonomously built for accelerated fundamental studies of the in‐flow metal cation doping of LHP NCs. The surrogate model of the sequential halide exchange and cation doping reactions of LHP NCs is then utilized for five closed‐loop synthesis campaigns with different target NC doping levels. The precise and intelligent NC synthesis and processing strategy, presented herein, can be further applied toward the autonomous discovery and development of novel impurity‐doped NCs with applications in next‐generation energy technologies.
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null (Ed.)Lead-free perovskites and their analogues have been extensively studied as a class of next-generation luminescent and optoelectronic materials. Herein, we report the synthesis of new colloidal Cs 4 M( ii )Bi 2 Cl 12 (M( ii ) = Cd, Mn) nanocrystals (NCs) with unique luminescence properties. The obtained Cs 4 M( ii )Bi 2 Cl 12 NCs show a layered double perovskite (LDP) crystal structure with good particle stability. Density functional theory calculations show that both samples exhibit a wide, direct bandgap feature. Remarkably, the strong Mn–Mn coupling effect of the Cs 4 M( ii )Bi 2 Cl 12 NCs results in an ultra-short Mn photoluminescence (PL) decay lifetime of around 10 μs, around two orders of magnitude faster than commonly observed Mn 2+ dopant emission in NCs. Diluting the Mn 2+ ion concentration through forming Cs 4 (Cd 1−x Mn x )Bi 2 Cl 12 (0 < x < 1) alloyed LDP NCs leads to prolonged PL lifetimes and enhanced PL quantum yields. Our study provides the first synthetic example of Bi-based LDP colloidal NCs with potential for serving as a new category of stable lead-free perovskite-type materials for various applications.more » « less
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Abstract Organic–inorganic hybrid perovskites have emerged as promising optoelectronic materials for applications in photovoltaic and optoelectronic devices. Particularly, 2D layer‐structured hybrid perovskites are of great interest due to their remarkable optical and electrical properties, which can be easily tuned by selecting suitable organic and inorganic moieties during the material synthesis. Here, the solution‐phase growth of a large square‐shaped single‐crystalline 2D hybrid perovskite, phenethylammonium lead bromide (C6H5C2H4NH3)2PbBr4(PEPB), with thickness as few as 3 unit cell layers is demonstrated. Compared to bulk crystals, the 2D PEPB nanocrystals show a major blueshifted photoluminescence (PL) peak at 409 nm indicating an increase in bandgap of 40 meV. Besides the major peak, two new PL peaks located at 480 and 525 nm are observed from the hybrid perovskite nanocrystals. PEPB nanocrystals with different thicknesses show different colors, which can be used to estimate the thickness of the nanocrystals. Time‐resolved reflectance spectroscopy is used to investigate the exciton dynamics, which exhibits a biexponential decay with an amplitude‐weighted lifetime of 16.7 ps. The high‐quality 2D (C6H5C2H4NH3)2PbBr4nanocrystals are expected to have high PL quantum efficiency and potential applications for light‐emitting devices.
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Lead halide perovskite nanocrystals possess incredible potential as next generation emitters due to their stellar set of optoelectronic properties. Unfortunately, their instability towards many ambient conditions and reliance on batch processing hinder their widespread utilities. Herein, we address both challenges by continuously synthesizing highly stable perovskite nanocrystals via integrating star-like block copolymer nanoreactors into a house-built flow reactor. Perovskite nanocrystals manufactured in this strategy display significantly enhanced colloidal, UV, and thermal stabilities over those synthesized with conventional ligands. Such scaling up of highly stable perovskite nanocrystals represents an important step towards their eventual use in many practical applications in optoelectronic materials and devices.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9CS00790C
