Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)
Letter 3
Au-CsPbBr Hybrid Architecture. Anchoring Gold Nanoparticles on Cubic Perovskite Nanocrystals Subila K Balakrishnan, and Prashant V. Kamat ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.6b00592 • Publication Date (Web): 29 Nov 2016 Downloaded from http://pubs.acs.org on November 30, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Energy Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Energy Letters
Au-CsPbBr3 Hybrid Architecture; Anchoring Gold Nanoparticles on Cubic Perovskite Nanocrystals
Subila K. Balakrishnan and Prashant V. Kamat* Radiation Laboratory Department of Chemistry & Biochemistry Notre Dame, IN 46556
Address correspondence to this author:
[email protected] or kamatlab.com
ACS Paragon Plus Environment
ACS Energy Letters
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 12
2 Abstract A selective growth of gold (Au) nanoparticles on the corners of CsPbBr3 nanocrystals (NCs) is made possible with the treatment of Au (III) salts such as Au (III) bromide and Au (III) chloride in solution. The surface bound oleylamine ligands not only stabilize NCs but also facilitate reduction of the Au(III) salts followed by nucleation of the Au nanoparticles on the corners of the perovskite NCs. The luminescence quantum yield of NCs is decreased when Au nanoparticles are formed on the corners of CsPbBr3 NCs suggesting interaction between the two systems. Formation of Au nanoparticles as well as an anion exchange is seen when Au(III) bromide was replaced with Au(III) chloride as a precursor. This simple strategy of designing perovskite-gold hybrid nanostructures with good colloidal stability offers new opportunities to explore their photocatalytic properties.
TOC Graphics
ACS Paragon Plus Environment
Page 3 of 12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Energy Letters
3 Organic and inorganic metal halide perovskites have been explored in recent years for photovoltaic applications.1-4 A certified power conversion efficiency of 22 % has been achieved for MAPbI3 perovskite based photovoltaic devices. The excellent optical and electronic properties of lead halide perovskites allow the use of this material, not only for the photovoltaic devices but also for LED and other optoelectronic devices.5-10 Efforts have been made recently to synthesize perovskite nanocrystals (NCs) of different size and composition so that their band gap can be tuned to match the desired spectrum.11-12 Additionally, the band gap of the perovskite, ABX3 (A: Monovalent cation; B: divalent cation and X: halide ions), can be tuned over the entire visible-IR spectral region by changing the all the three A, B and X ions in the crystal lattice.13-17 Banin and co-workers have developed a simple method for the selective growth of gold (Au) dots (1.5 nm size) onto the tips of colloidal semiconductor nanorods (CdSe-Au tipped rods) as these metalsemiconductor heterojunctions provide new functionality to the nanostructures.18 Such gold-tipped nanostructures provide natural contact points which can be used for nanoscale device fabrication. The presence of Au metal at the semiconductor nanostructure is known to induce plasmonic field effects thus influencing their photocatalytic and photovoltaic performance.19-20 Exciton-plasmon interactions can also influence the excited state deactivation as evident from the decreased photoluminescence quantum yield in such semiconductor-metal hybrid systems.21 The possibility of synthesizing highly luminescent CsPbBr3 nanocrystals has enabled researchers to investigate many interesting optical and electronic properties.22-25 Yet, their interaction with metal nanoparticles are yet to be explored. We have recently shown the conversion of cubic phase CsPbBr3 films into cubic CsPbI3 through halide ion exchange.26 Herein we show a simple strategy to anchor gold (Au) nanoparticles on the corner of cubic CsPbBr3 nanocrystals without destroying the lattice structure while maintaining a good colloidal stability. CsPbBr3
NCs were synthesised by reacting Cs-oleate with Pb (II)-bromide using a modified
methodology reported earlier.22-26 The PbBr2 (0.19 mmol) was dissolved first in octadecene (high boiling point solvent, 5 ml) in a three-neck flask. Oleylamine (1.52 mmol) and oliec acid (1.58 mmol) were introduced into the flask under argon atmosphere (details are included in the supporting information). Cs-oleate (0.046 mmol) was injected into the flask at 150oC. CsPbBr3 formed in the flask was separated by precipitation with butanol-acetone mixture followed by centrifugation. The purified NCs were then redispersed in the toluene for further studies. The elemental analyses by energy dispersive x-ray (EDX) spectroscopy confirmed the 1:1:3 atomic ratios for the sample prepared using this method (EDX spectra and atomic composition is included in the supporting information, section 3).
ACS Paragon Plus Environment
ACS Energy Letters
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 12
4 The absorption and emission spectra of colloidal CsPbBr3 in toluene are presented in Figure 1. The NCs show a bright photoluminescence (Quantum yield: 80%; vs Rhodamine 6G in ethanol (0.95)) with emission maximum at 515nm. A narrow full-width at half maximum (23 nm) confirmed the monodispersity of CsPbBr3 NCs. TEM (transmission electron microscopy) analyses indicate that the cubic CsPbBr3 NCs are monodisperse and their size is estimated to be 7nm (Figure 2A). The colloidal stability of CsPbBr3 NCs in organic solvents depends on the surface chemistry of ligands coordinated to the nanocrystals. In the case of CsPbBr3 NCs, the surface chemistry is dictated by oleylamine and oleic acid. Recently, Hens and co-workers have illustrated the chemical reactivity such ligands bound to the surface of NCs.27 The termination of the CsPbBr3 NCs with PbBr64- anions leaves the surface negatively charged. Furthermore, a dynamic equilibrium between the coordinated and uncoordinated ligands on the surface influences the binding of oleic acid and oleylamine ligands, thus providing stability to the NC suspension. Au-CsPbBr3 Hybrid Nanocrystals. We have designed a simple strategy of utilizing the ligand surface chemistry to reduce Au salts directly on the NCs and create Au-CsPbBr3 hybrid structures. As shown earlier alkyl and aryl amines are capable of reducing Au(III) ions in organic solvents and to form Au0 and subsequent formation of Au nanoparticles.28 In order to execute this approach, we incorporated known amount (1 mmol) of AuBr3 crystals into the toluene solution (3 ml) containing CsPbBr3 NCs under ambient conditions. (The concentration of CsPbBr3 was 40 µM and was calculated based using reported molar extinction coefficient. The details are included in the supporting information section
Au Au CsPbBr3
CsPbBr3
Au CsPb(Br1-xClx)3 Au R-NH2, Oleylamine
Au
R-COOH, Oleic acid RNH2 & [R-NH3]+BrAu (III) (AuBr3/AuCl3)
Au (0)nuclei Room temperature, < 1 min
Au (0)nuclei
Au (NP)
Scheme 1. Surface chemistry of ligands leading to the reduction of Au(III) at CsPbBr3 NCs to ACS Paragon Plus Environment provide Au-CsPbBr3 hybrid structures
Page 5 of 12
5 S12.) The reaction was spontaneous (
