251
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Liu X, Zhou J, Zheng J, Becker ML, Gong X. Water-soluble CdTe quantum dots as an anode interlayer for solution-processed near infrared polymer photodetectors. NANOSCALE 2013; 5:12474-12479. [PMID: 24166538 DOI: 10.1039/c3nr03602b] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Water-soluble cadmium telluride (CdTe) quantum dots (QDs) used as an anode interlayer in solution-processed near infrared (NIR) polymer photodetectors (PDs) were demonstrated. Polymer PDs incorporated with CdTe QDs as an anode interlayer exhibited 10-fold suppressed dark current density and analogous photocurrent density relative to poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which resulted in enhanced detectivities over 10(11) Jones in the spectral range from 350 nm to 900 nm. Moreover, with the substitution of PEDOT:PSS by CdTe QDs, the stability of unencapsulated NIR polymer PDs was extended up to 650 hours, which is more than 3 times longer than those with PEDOT:PSS as an anode interlayer. These results indicated that CdTe QDs can be utilized as a solution-processable alternative to PEDOT:PSS as an anode interlayer for high performance NIR polymer PDs.
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Affiliation(s)
- Xilan Liu
- College of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH 44325, USA.
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252
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Anderson NC, Hendricks MP, Choi JJ, Owen JS. Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: spectroscopic observation of facile metal-carboxylate displacement and binding. J Am Chem Soc 2013; 135:18536-48. [PMID: 24199846 PMCID: PMC4102385 DOI: 10.1021/ja4086758] [Citation(s) in RCA: 430] [Impact Index Per Article: 39.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
We demonstrate that metal carboxylate complexes (L-M(O2CR)2, R = oleyl, tetradecyl, M = Cd, Pb) are readily displaced from carboxylate-terminated ME nanocrystals (ME = CdSe, CdS, PbSe, PbS) by various Lewis bases (L = tri-n-butylamine, tetrahydrofuran, tetradecanol, N,N-dimethyl-n-butylamine, tri-n-butylphosphine, N,N,N',N'-tetramethylbutylene-1,4-diamine, pyridine, N,N,N',N'-tetramethylethylene-1,2-diamine, n-octylamine). The relative displacement potency is measured by (1)H NMR spectroscopy and depends most strongly on geometric factors such as sterics and chelation, although also on the hard/soft match with the cadmium ion. The results suggest that ligands displace L-M(O2CR)2 by cooperatively complexing the displaced metal ion as well as the nanocrystal. Removal of up to 90% of surface-bound Cd(O2CR)2 from CdSe and CdS nanocrystals decreases the Cd/Se ratio from 1.1 ± 0.06 to 1.0 ± 0.05, broadens the 1S(e)-2S(3/2h) absorption, and decreases the photoluminescence quantum yield (PLQY) from 10% to <1% (CdSe) and from 20% to <1% (CdS). These changes are partially reversed upon rebinding of M(O2CR)2 at room temperature (∼60%) and fully reversed at elevated temperature. A model is proposed in which electron-accepting M(O2CR)2 complexes (Z-type ligands) reversibly bind to nanocrystals, leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, but are instead dynamic structures with concentration-dependent compositions. The importance of these findings to the synthesis and purification of nanocrystals as well as ligand exchange reactions is discussed.
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Affiliation(s)
- Nicholas C. Anderson
- Department of Chemistry, Columbia University, 3000 Broadway, MC 3121, New York, NY 10027
| | - Mark P. Hendricks
- Department of Chemistry, Columbia University, 3000 Broadway, MC 3121, New York, NY 10027
| | - Joshua J. Choi
- Department of Chemistry, Columbia University, 3000 Broadway, MC 3121, New York, NY 10027
| | - Jonathan S. Owen
- Department of Chemistry, Columbia University, 3000 Broadway, MC 3121, New York, NY 10027
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253
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Wang H, McNellis ER, Kinge S, Bonn M, Cánovas E. Tuning electron transfer rates through molecular bridges in quantum dot sensitized oxides. NANO LETTERS 2013; 13:5311-5315. [PMID: 24093529 DOI: 10.1021/nl402820v] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Photoinduced electron transfer processes from semiconductor quantum dots (QDs) molecularly bridged to a mesoporous oxide phase are quantitatively surveyed using optical pump-terahertz probe spectroscopy. We control electron transfer rates in donor-bridge-acceptor systems by tuning the electronic coupling strength through the use of n-methylene (SH-[CH2]n-COOH) and n-phenylene (SH-[C6H4](n)-COOH) molecular bridges. Our results show that electron transfer occurs as a nonresonant quantum tunneling process with characteristic decay rates of β(n) = 0.94 ± 0.08 and β(n) = 1.25 per methylene and phenylene group, respectively, in quantitative agreement with reported conductance measurements through single molecules and self-assembled monolayers. For a given QD donor-oxide acceptor separation distance, the aromatic n-phenylene based bridges allow faster electron transfer processes when compared with n-methylene based ones. Implications of these results for QD sensitized solar cell design are discussed.
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Affiliation(s)
- Hai Wang
- Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany
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254
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Axnanda S, Scheele M, Crumlin E, Mao B, Chang R, Rani S, Faiz M, Wang S, Alivisatos AP, Liu Z. Direct work function measurement by gas phase photoelectron spectroscopy and its application on PbS nanoparticles. NANO LETTERS 2013; 13:6176-6182. [PMID: 24175587 DOI: 10.1021/nl403524a] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Work function is a fundamental property of a material's surface. It is playing an ever more important role in engineering new energy materials and efficient energy devices, especially in the field of photovoltaic devices, catalysis, semiconductor heterojunctions, nanotechnology, and electrochemistry. Using ambient pressure X-ray photoelectron spectroscopy (APXPS), we have measured the binding energies of core level photoelectrons of Ar gas in the vicinity of several reference materials with known work functions (Au(111), Pt(111), graphite) and PbS nanoparticles. We demonstrate an unambiguously negative correlation between the work functions of reference samples and the binding energies of Ar 2p core level photoelectrons detected from the Ar gas near the sample surface region. Using this experimentally determined linear relationship between the surface work function and Ar gas core level photoelectron binding energy, we can measure the surface work function of different materials under different gas environments. To demonstrate the potential applications of this ambient pressure XPS technique in nanotechnology and solar energy research, we investigate the work functions of PbS nanoparticles with various capping ligands: methoxide, mercaptopropionic acid, and ethanedithiol. Significant Fermi level position changes are observed for PbS nanoparticles when the nanoparticle size and capping ligands are varied. The corresponding changes in the valence band maximum illustrate that an efficient quantum dot solar cell design has to take into account the electrochemical effect of the capping ligand as well.
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Affiliation(s)
- Stephanus Axnanda
- Advanced Light Source Division and ‡Material Science Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720
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255
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Malicki M, Knowles KE, Weiss EA. Gating of hole transfer from photoexcited PbS quantum dots to aminoferrocene by the ligand shell of the dots. Chem Commun (Camb) 2013; 49:4400-2. [PMID: 22684304 DOI: 10.1039/c2cc32895j] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Photoinduced hole transfer from PbS quantum dots (QDs) to aminoferrocene only occurs if the ligand shell of the QD allows aminoferrocene to gain direct access to the inorganic core of the QD; the permeability of the ligand shell is therefore more important than its conductivity in determining the probability of interfacial charge transfer.
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Affiliation(s)
- Michał Malicki
- Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, IL 60208-3113, USA
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256
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Koh WK, Koposov AY, Stewart JT, Pal BN, Robel I, Pietryga JM, Klimov VI. Heavily doped n-type PbSe and PbS nanocrystals using ground-state charge transfer from cobaltocene. Sci Rep 2013; 3:2004. [PMID: 23774224 PMCID: PMC3684816 DOI: 10.1038/srep02004] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Accepted: 05/30/2013] [Indexed: 12/23/2022] Open
Abstract
Colloidal nanocrystals (NCs) of lead chalcogenides are a promising class of tunable infrared materials for applications in devices such as photodetectors and solar cells. Such devices typically employ electronic materials in which charge carrier concentrations are manipulated through “doping;” however, persistent electronic doping of these NCs remains a challenge. Here, we demonstrate that heavily doped n-type PbSe and PbS NCs can be realized utilizing ground-state electron transfer from cobaltocene. This allows injecting up to eight electrons per NC into the band-edge state and maintaining the doping level for at least a month at room temperature. Doping is confirmed by inter- and intra-band optical absorption, as well as by carrier dynamics. Finally, FET measurements of doped NC films and the demonstration of a p-n diode provide additional evidence that the developed doping procedure allows for persistent incorporation of electrons into the quantum-confined NC states.
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Affiliation(s)
- Weon-kyu Koh
- Center for Advanced Solar Photophysics, Los Alamos National Laboratory, New Mexico 87545, United States
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257
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Kawawaki T, Tatsuma T. Enhancement of PbS quantum dot-sensitized photocurrents using plasmonic gold nanoparticles. Phys Chem Chem Phys 2013; 15:20247-51. [DOI: 10.1039/c3cp53625d] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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258
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Chiu SC, Jhang JS, Chen JF, Fang J, Jian WB. Effects of cross-sectional area on the tunneling-junction array in octahedral PbSe colloidal-nanocrystal solids. Phys Chem Chem Phys 2013; 15:16127-31. [PMID: 23985927 DOI: 10.1039/c3cp52083h] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Octahedral PbSe colloidal nanocrystals (NCs) are used to assemble a solid. Because of the special feature of the apexes of the octahedrons, the cross-sectional area of the inter-dot tunneling junctions is much smaller than that formed between spherical NCs. The inter-dot separation between NCs is easily adjusted by mild thermal treatment. Like a spherical NC-solid, the resistance of the octahedral NC-solid is exponentially dependent on the inter-dot separation. On the contrary, due to the difference in the cross-sectional area between the NCs, electron transport in the octahedral NC-solid does not follow the same model used for the explanation of electron transport in a spherical NC-solid. Through analyses of current-voltage and resistance-temperature behaviors, we have confirmed that the model of fluctuation-induced tunneling conduction fits very well with all of the data and explains the variation in the electrical properties of octahedral PbSe colloidal NC-solids after thermal annealing.
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Affiliation(s)
- Shao-Chien Chiu
- Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan.
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259
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Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange. Proc Natl Acad Sci U S A 2013; 110:16716-23. [PMID: 24082134 DOI: 10.1073/pnas.1316755110] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Unique tripodal S-donor capping agents with an attached carboxylate are found to bind tightly to the surface of CdSe nanocrystals (NCs), making the latter water soluble. Unlike that in similarly solubilized CdSe NCs with one-sulfur or two-sulfur capping agents, dissociation from the NC surface is greatly reduced. The impact of this behavior is seen in the photochemical generation of H2 in which the CdSe NCs function as the light absorber with metal complexes in aqueous solution as the H2-forming catalyst and ascorbic acid as the electron donor source. This precious-metal-free system for H2 generation from water using [Co(bdt)2](-) (bdt, benzene-1,2-dithiolate) as the catalyst exhibits excellent activity with a quantum yield for H2 formation of 24% at 520 nm light and durability with >300,000 turnovers relative to catalyst in 60 h.
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260
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Elward JM, Chakraborty A. Effect of Dot Size on Exciton Binding Energy and Electron-Hole Recombination Probability in CdSe Quantum Dots. J Chem Theory Comput 2013; 9:4351-9. [PMID: 26589152 DOI: 10.1021/ct400485s] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Jennifer M Elward
- Department of Chemistry, Syracuse University , Syracuse, New York 13244, United States
| | - Arindam Chakraborty
- Department of Chemistry, Syracuse University , Syracuse, New York 13244, United States
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261
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Luber EJ, Mobarok MH, Buriak JM. Solution-processed zinc phosphide (α-Zn3P2) colloidal semiconducting nanocrystals for thin film photovoltaic applications. ACS NANO 2013; 7:8136-8146. [PMID: 23952612 DOI: 10.1021/nn4034234] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Zinc phosphide (Zn3P2) is a promising earth-abundant material for thin film photovoltaic applications, due to strong optical absorption and near ideal band gap. In this work, crystalline zinc phosphide nanoparticles are synthesized using dimethylzinc and tri-n-octylphosphine as precursors. Transmission electron microscopy and X-ray diffraction data show that these nanoparticles have an average diameter of ∼8 nm and adopt the crystalline structure of tetragonal α-Zn3P2. The optical band gap is found to increase by 0.5 eV relative to bulk Zn3P2, while there is an asymmetric shift in the conduction and valence band levels. Utilizing layer-by-layer deposition of Zn3P2 nanoparticle films, heterojunction devices consisting of ITO/ZnO/Zn3P2/MoO3/Ag are fabricated and tested for photovoltaic performance. The devices are found to exhibit excellent rectification behavior (rectification ratio of 600) and strong photosensitivity (on/off ratio of ∼10(2)). X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy analyses reveal the presence of a thin 1.5 nm phosphorus shell passivating the surface of the Zn3P2 nanoparticles. This shell is believed to form during the nanoparticle synthesis.
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Affiliation(s)
- Erik J Luber
- National Institute for Nanotechnology (NINT), National Research Counci l, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada
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262
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Chiu SC, Jhang JS, Lin YF, Hsu SY, Fang J, Jian WB. Nanocrystal shape and nanojunction effects on electron transport in nanocrystal-assembled bulks. NANOSCALE 2013; 5:8555-8559. [PMID: 23892514 DOI: 10.1039/c3nr01418e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Bulk nanostructured materials are made from the assembly of octahedral PbSe nanocrystals. After thermal annealing, the artificial bulk demonstrates a large difference in behavior depending on the temperature, and a large variation of room-temperature resistivity of up to seven orders of magnitude. This variation originates from the high-indexed sharp edges of the octahedral nanocrystals. As the nanocrystals are arranged in the edge-to-edge configuration, which was observed in scanning electron microscopy images, the inter-nanocrystal capacitance is small due to the small parallel area between the nanocrystals. The small capacitance results in a high thermal fluctuation voltage and drives electron transport. The temperature-dependent resistivity and the electric field-dependent current are highly in agreement with the model of fluctuation-induced tunneling conduction. Thermal annealing reduces the inter-nanocrystal separation distance, creating a large variation in the electrical properties. Specifically, octahedral-shaped PbSe nanocrystals are employed in tailoring the electron transport in bulk nanostructured materials.
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Affiliation(s)
- Shao-Chien Chiu
- Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan, ROC
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263
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Kramer IJ, Sargent EH. The Architecture of Colloidal Quantum Dot Solar Cells: Materials to Devices. Chem Rev 2013; 114:863-82. [DOI: 10.1021/cr400299t] [Citation(s) in RCA: 401] [Impact Index Per Article: 36.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Illan J. Kramer
- Edward S. Rogers Department of Electrical & Computer Engineering, University of Toronto, 10 King’s College Road, Toronto, Ontario M5S 3G4, Canada
| | - Edward H. Sargent
- Edward S. Rogers Department of Electrical & Computer Engineering, University of Toronto, 10 King’s College Road, Toronto, Ontario M5S 3G4, Canada
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264
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Sashchiuk A, Yanover D, Rubin-Brusilovski A, Maikov GI, Čapek RK, Vaxenburg R, Tilchin J, Zaiats G, Lifshitz E. Tuning of electronic properties in IV-VI colloidal nanostructures by alloy composition and architecture. NANOSCALE 2013; 5:7724-7745. [PMID: 23857167 DOI: 10.1039/c3nr02141f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Colloidal lead chalcogenide (IV-VI) quantum dots and rods are of widespread scientific and technological interest, owing to their size tunable energy band gap at the near-infrared optical regime. This article reviews the development and investigation of IV-VI derivatives, consisting of a core (dot or rod) coated with an epitaxial shell, when either the core or the shell (or both) has an alloy composition, so the entire structure has the chemical formula PbSexS1-x/PbSeyS1-y (0 ≤ x(y) ≤ 1). The article describes synthesis procedures and an examination of the structures' chemical and temperature stability. The investigation of the optical properties revealed information about the quantum yield, radiative lifetime, emission's Stokes shift and electron-phonon interaction, on the variation of composition, core-to-shell division, temperature and environment. The study reflected the unique properties of core-shell heterostructures, offering fine electronic tuning (at a fixed size) by changing their architecture. The optical observations are supported by the electronic band structure theoretical model. The challenges related to potential applications of the colloidal lead chalcogenide quantum dots and rods are also briefly addressed in the article.
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Affiliation(s)
- Aldona Sashchiuk
- Schulich Faculty of Chemistry, Russell Berrie Nanotechnology Institute, Solid State Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel
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265
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Peterson MD, Holbrook RJ, Meade TJ, Weiss EA. Photoinduced electron transfer from PbS quantum dots to cobalt(III) Schiff base complexes: light activation of a protein inhibitor. J Am Chem Soc 2013; 135:13162-7. [PMID: 23931454 DOI: 10.1021/ja4065393] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
This paper describes the activation of a biologically inert Co(III) Schiff base [Co(III)-SB] complex to its protein inhibitor form by photoinduced electron transfer (PET) from a colloidal PbS quantum dot (QD, radii of 1.5-1.7 nm) to the cobalt center, with a charge separation time constant of 125 ns. Reduction of the Co(III)-SB complex initiates release of the native axial ligands, promoting replacement with the histidine mimic 4-methylimidazole. The rate of ligand displacement increases by a factor of approximately 8 upon exposure of the PbS QD/Co(III)-SB mixture to light with an energy greater than the energy of the first excitonic state of the QDs, from which PET occurs. These results suggest an approach for the preparation of inorganic therapeutic agents that can be specifically coupled to a biologically active site by cooperative redox binding ligation.
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Affiliation(s)
- Mark D Peterson
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
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266
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King PW. Designing interfaces of hydrogenase–nanomaterial hybrids for efficient solar conversion. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:949-57. [DOI: 10.1016/j.bbabio.2013.03.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Accepted: 03/18/2013] [Indexed: 11/28/2022]
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267
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Pan Z, Zhao K, Wang J, Zhang H, Feng Y, Zhong X. Near infrared absorption of CdSe(x)Te(1-x) alloyed quantum dot sensitized solar cells with more than 6% efficiency and high stability. ACS NANO 2013; 7:5215-5222. [PMID: 23705771 DOI: 10.1021/nn400947e] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
CdSe0.45Te0.55 alloyed quantum dots (QDs) with excitonic absorption onset at 800 nm and particle size of 5.2 nm were prepared via a noninjection high-temperature pyrolysis route and used as a sensitizer in solar cells. A postsynthesis assembly approach with use of bifunctional linker molecule mercaptopropionic acid (MPA) capped water-soluble QDs, obtained via ex situ ligand exchange from the initial oil-dispersible QDs, was adopted for tethering QDs onto mesoporous TiO2 film. With the combination of high loading of the QD sensitizer and intrinsic superior optoelectronic properties (wide absorption range, high conduction band edge, high chemical stability, etc., relative to their constituents CdSe and CdTe) of the adopted CdSe0.45Te0.55 QD sensitizer, the resulting CdSexTe1-x alloyed QD-based solar cells exhibit a record conversion efficiency of 6.36% (Jsc = 19.35 mA/cm(2), Voc = 0.571 V, FF = 0.575) under full 1 sun illumination, which is remarkably better than that of the reference CdSe and CdTe QD based ones. Furthermore, the solar cells with Cu2S counter electrodes based on eletrodeposition of Cu on conductive glass show long-term (more than 500 h) stability.
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Affiliation(s)
- Zhenxiao Pan
- State Key Laboratory of Bioreactor Engineering, Institute of Applied Chemistry, East China University of Science and Technology, Shanghai 200237, China
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268
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Son JS, Lee JS, Shevchenko EV, Talapin DV. Magnet-in-the-Semiconductor Nanomaterials: High Electron Mobility in All-Inorganic Arrays of FePt/CdSe and FePt/CdS Core-Shell Heterostructures. J Phys Chem Lett 2013; 4:1918-23. [PMID: 26283129 DOI: 10.1021/jz400612d] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We report a colloidal synthesis and electrical and magnetotransport properties of multifunctional "magnet-in-the-semiconductor" nanostructures composed of FePt core and CdSe or CdS shell. Thin films of all-inorganic FePt/CdSe and FePt/CdS core-shell nanostructures capped with In2Se4(2-) molecular chalcogenide (MCC) ligands exhibited n-type charge transport with high field-effect electron mobility of 3.4 and 0.02 cm(2)/V·s, respectively. These nanostructures also showed a negative magnetoresistance characteristic for spin-dependent tunneling. We discuss the mechanism of charge transport and gating in the arrays of metal/semiconductor core-shell nanostructures.
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Affiliation(s)
- Jae Sung Son
- †Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Jong-Soo Lee
- †Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
- ‡Department of Energy Systems Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu 711-873, South Korea
| | - Elena V Shevchenko
- §Center for Nanoscale Materials, Argonne National Lab, Argonne, Illinois 60439, United States
| | - Dmitri V Talapin
- †Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
- §Center for Nanoscale Materials, Argonne National Lab, Argonne, Illinois 60439, United States
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269
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Jean J, Chang S, Brown PR, Cheng JJ, Rekemeyer PH, Bawendi MG, Gradečak S, Bulović V. ZnO nanowire arrays for enhanced photocurrent in PbS quantum dot solar cells. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2013; 25:2790-6. [PMID: 23440957 DOI: 10.1002/adma.201204192] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2012] [Revised: 11/24/2012] [Indexed: 05/11/2023]
Abstract
Vertical arrays of ZnO nanowires can decouple light absorption from carrier collection in PbS quantum dot solar cells and increase power conversion efficiencies by 35%. The resulting ordered bulk heterojunction devices achieve short-circuit current densities in excess of 20 mA cm(-2) and efficiencies of up to 4.9%.
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Affiliation(s)
- Joel Jean
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA
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270
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Califano M, Gómez-Campos FM. Universal trapping mechanism in semiconductor nanocrystals. NANO LETTERS 2013; 13:2047-2052. [PMID: 23627433 DOI: 10.1021/nl4003014] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Size tunability of the optical properties and inexpensive synthesis make semiconductor nanocrystals one of the most promising and versatile building blocks for many modern applications such as lasers, single-electron transistors, solar cells, and biological labels. The performance of these nanocrystal-based devices is however compromised by efficient trapping of the charge carriers. This process exhibits different features depending on the nanocrystal material, surface termination, size, and trap location, leading to the assumption that different mechanisms are at play in each situation. Here we revolutionize this fragmented picture and provide a unified interpretation of trapping dynamics in semiconductor nanocrystals by identifying the origins of this so far elusive detrimental process. Our findings pave the way for a general suppression strategy, applicable to any system, which can lead to a simultaneous efficiency enhancement in all nanocrystal-based technologies.
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Affiliation(s)
- Marco Califano
- Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom.
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271
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Knowles KE, Malicki M, Parameswaran R, Cass LC, Weiss EA. Spontaneous Multielectron Transfer from the Surfaces of PbS Quantum Dots to Tetracyanoquinodimethane. J Am Chem Soc 2013; 135:7264-71. [DOI: 10.1021/ja4003074] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kathryn E. Knowles
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Michał Malicki
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Radha Parameswaran
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Laura C. Cass
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Emily A. Weiss
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States
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272
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Akhavan S, Gungor K, Mutlugun E, Demir HV. Plasmonic light-sensitive skins of nanocrystal monolayers. NANOTECHNOLOGY 2013; 24:155201. [PMID: 23519189 DOI: 10.1088/0957-4484/24/15/155201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We report plasmonically coupled light-sensitive skins of nanocrystal monolayers that exhibit sensitivity enhancement and spectral range extension with plasmonic nanostructures embedded in their photosensitive nanocrystal platforms. The deposited plasmonic silver nanoparticles of the device increase the optical absorption of a CdTe nanocrystal monolayer incorporated in the device. Controlled separation of these metallic nanoparticles in the vicinity of semiconductor nanocrystals enables optimization of the photovoltage buildup in the proposed nanostructure platform. The enhancement factor was found to depend on the excitation wavelength. We observed broadband sensitivity improvement (across 400-650 nm), with a 2.6-fold enhancement factor around the localized plasmon resonance peak. The simulation results were found to agree well with the experimental data. Such plasmonically enhanced nanocrystal skins hold great promise for large-area UV/visible sensing applications.
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Affiliation(s)
- Shahab Akhavan
- UNAM-Institute of Materials Science and Nanotechnology, Department of Electrical and Electronics Engineering and Department of Physics, Bilkent University, Ankara, Turkey
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273
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Zhang Z, Li D, Xie R, Yang W. Insights into the Energy Levels of Semiconductor Nanocrystals by a Dopant Approach. Angew Chem Int Ed Engl 2013; 52:5052-5. [DOI: 10.1002/anie.201210080] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 02/21/2013] [Indexed: 11/08/2022]
Affiliation(s)
- Zhuolei Zhang
- College of Chemistry, Jilin University, Changchun, 130012 (P.R. China)
| | - Dongze Li
- College of Chemistry, Jilin University, Changchun, 130012 (P.R. China)
| | - Renguo Xie
- College of Chemistry, Jilin University, Changchun, 130012 (P.R. China)
| | - Wensheng Yang
- College of Chemistry, Jilin University, Changchun, 130012 (P.R. China)
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274
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Insights into the Energy Levels of Semiconductor Nanocrystals by a Dopant Approach. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201210080] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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275
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Boehme SC, Wang H, Siebbeles LDA, Vanmaekelbergh D, Houtepen AJ. Electrochemical charging of CdSe quantum dot films: dependence on void size and counterion proximity. ACS NANO 2013; 7:2500-8. [PMID: 23398747 DOI: 10.1021/nn3058455] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Films of colloidal quantum dots (QDs) show great promise for application in optoelectronic devices. Great advances have been made in recent years in designing efficient QD solar cells and LEDs. A very important aspect in the design of devices based on QD films is the knowledge of their absolute energy levels. Unfortunately, reported energy levels vary markedly depending on the employed measurement technique and the environment of the sample. In this report, we determine absolute energy levels of QD films by electrochemical charge injection. The concomitant change in optical absorption of the film allows quantification of the number of charges in quantum-confined levels and thereby their energetic position. We show here that the size of voids in the QD films (i.e., the space between the quantum dots) determines the amount of charges that may be injected into the films. This effect is attributed to size exclusion of countercharges from the electrolyte solution. Further, the energy of the QD levels depends on subtle changes in the QD film and the supporting electrolyte: the size of the cation and the QD ligand length. These nontrivial effects can be explained by the proximity of the cation to the QD surface and a concomitant lowering of the electrochemical potential. Our findings help explain the wide range of reported values for QD energy levels and redefine the limit of applicability of electrochemical measurements on QD films. Finally, the finding that the energy of QD levels depends on ligand length and counterion size may be exploited in optimized designs of QD sensitized solar cells.
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Affiliation(s)
- Simon C Boehme
- Chemical Engineering, Optoelectronic Materials, TU Delft, Julianalaan 136, 2628 BL Delft, The Netherlands
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276
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Nanayakkara SU, Cohen G, Jiang CS, Romero MJ, Maturova K, Al-Jassim M, van de Lagemaat J, Rosenwaks Y, Luther JM. Built-in potential and charge distribution within single heterostructured nanorods measured by scanning Kelvin probe microscopy. NANO LETTERS 2013; 13:1278-1284. [PMID: 23379602 DOI: 10.1021/nl4000147] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The electrostatic potential distribution across single, isolated, colloidal heterostructured nanorods (NRs) with component materials expected to form a p-n junction within each NR has been measured using scanning Kelvin probe microscopy (SKPM). We compare CdS to bicomponent CdS-CdSe, CdS-PbSe, and CdS-PbS NRs prepared via different synthetic approaches to corroborate the SKPM assignments. The CdS-PbS NRs show a sharp contrast in measured potential across the material interface. We find the measured built-in potential within an individual NR to be attenuated by long-range electrostatic forces between the sample substrate, cantilever, and the measuring tip. Surface potential images were deconvoluted to yield built-in potentials ranging from 375 to 510 meV in the heterostructured NRs. We deduce the overall built-in potential as well as the charge distribution across each segment of the heterostructured NRs by combining SKPM data with simulations of the system.
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Affiliation(s)
- Sanjini U Nanayakkara
- National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado, United States
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277
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Maier-Flaig F, Rinck J, Stephan M, Bocksrocker T, Bruns M, Kübel C, Powell AK, Ozin GA, Lemmer U. Multicolor silicon light-emitting diodes (SiLEDs). NANO LETTERS 2013; 13:475-80. [PMID: 23320768 DOI: 10.1021/nl3038689] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We present highly efficient electroluminescent devices using size-separated silicon nanocrystals (ncSi) as light emitting material. The emission color can be tuned from the deep red down to the yellow-orange spectral region by using very monodisperse size-separated nanoparticles. High external quantum efficiencies up to 1.1% as well as low turn-on voltages are obtained for red emitters. In addition, we demonstrate that size-separation of ncSi leads to drastically improved lifetimes of the devices and much less sensitivity of the emission wavelength to the applied drive voltage.
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Affiliation(s)
- Florian Maier-Flaig
- Light Technology Institute (LTI) and DFG Center for Functional Nanostructures, Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany.
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278
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Frederick MT, Amin VA, Swenson NK, Ho AY, Weiss EA. Control of exciton confinement in quantum dot-organic complexes through energetic alignment of interfacial orbitals. NANO LETTERS 2013; 13:287-292. [PMID: 23244048 DOI: 10.1021/nl304098e] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
This paper describes a method to control the quantum confinement, and therefore the energy, of excitonic holes in CdSe QDs through adsorption of the hole-delocalizing ligand phenyldithiocarbamate, PTC, and para substitutions of the phenyl ring of this ligand with electron-donating or -withdrawing groups. These substitutions control hole delocalization in the QDs through the energetic alignment of the highest occupied orbitals of PTC with the highest density-of-states region of the CdSe valence band, to which PTC couples selectively.
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Affiliation(s)
- Matthew T Frederick
- Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208-3113, USA
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279
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Pazhanivel T, Devarajan VP, Bharathi G, Senthil K, Ganapathy V, Yong K, Nataraj D. Systematic investigation of the structure and photophysical properties of CdSe, CdSe/ZnS QDs and their hybrid with β-carotene. RSC Adv 2013. [DOI: 10.1039/c3ra41482e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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280
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Selinsky RS, Ding Q, Faber MS, Wright JC, Jin S. Quantum dot nanoscale heterostructures for solar energy conversion. Chem Soc Rev 2013; 42:2963-85. [DOI: 10.1039/c2cs35374a] [Citation(s) in RCA: 192] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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281
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Watanabe H, Fujikata K, Oaki Y, Imai H. Band-gap expansion of tungsten oxide quantum dots synthesized in sub-nano porous silica. Chem Commun (Camb) 2013; 49:8477-9. [DOI: 10.1039/c3cc44264k] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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282
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Jadhav PJ, Brown PR, Thompson N, Wunsch B, Mohanty A, Yost SR, Hontz E, Van Voorhis T, Bawendi MG, Bulović V, Baldo MA. Triplet exciton dissociation in singlet exciton fission photovoltaics. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:6169-6174. [PMID: 22968762 DOI: 10.1002/adma.201202397] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 07/23/2012] [Indexed: 06/01/2023]
Abstract
Triplet exciton dissociation in singlet exciton fission devices with three classes of acceptors are characterized: fullerenes, perylene diimides, and PbS and PbSe colloidal nanocrystals. Using photocurrent spectroscopy and a magnetic field probe it is found that colloidal PbSe nanocrystals are the most promising acceptors, capable of efficient triplet exciton dissociation and long wavelength absorption.
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Affiliation(s)
- Priya J Jadhav
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA
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283
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Grandhi GK, Tomar R, Viswanatha R. Study of surface and bulk electronic structure of II-VI semiconductor nanocrystals using Cu as a nanosensor. ACS NANO 2012; 6:9751-9763. [PMID: 23075251 DOI: 10.1021/nn304149s] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Efficiency of the quantum dots based solar cells relies on charge transfer at the interface and hence on the relative alignment of the energy levels between materials. Despite a high demand to obtain size specific band offsets, very few studies exist where meticulous methods like photoelectron spectroscopy are used. However, semiconductor charging during measurements could result in indirect and possibly inaccurate measurements due to shift in valence and conduction band position. Here, in this report, we devise a novel method to study the band offsets by associating an atomic like state with the conduction band and hence obtaining an internal standard. This is achieved by doping copper in semiconductor nanocrystals, leading to the development of a characteristic intragap Cu-related emission feature assigned to the transition from the conduction band to the atomic-like Cu d state. Using this transition we determine the relative band alignment of II-VI semiconductor nanocrystals as a function of size in the below 10 nm size regime. The results are in excellent agreement with the available photoelectron spectroscopy data as well as the theoretical data. We further use this technique to study the excitonic band edge variation as a function of temperature in CdSe nanocrystals. Additionally, surface electronic structure of CdSe nanocrystals have been studied using quantitative measurements of absolute quantum yield and PL decay studies of the Cu related emission and the excitonic emission. The role of TOP and oleic acid as surface passivating ligand molecules has been studied for the first time.
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Affiliation(s)
- G Krishnamurthy Grandhi
- New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, P.O., Jakkur, Bangalore 560064, India
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284
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Han Z, Qiu F, Eisenberg R, Holland PL, Krauss TD. Robust Photogeneration of H2 in Water Using Semiconductor Nanocrystals and a Nickel Catalyst. Science 2012; 338:1321-4. [DOI: 10.1126/science.1227775] [Citation(s) in RCA: 655] [Impact Index Per Article: 54.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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285
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Liang J, Zhang G. TiO₂ nanotip arrays: anodic fabrication and field-emission properties. ACS APPLIED MATERIALS & INTERFACES 2012; 4:6053-6061. [PMID: 23106725 DOI: 10.1021/am301690f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In contrast to the main-stream strategy of growing convex nanostructures upward from the substrates and using them as cold electron sources, it is illustrated in this article that growing concave nanostructures downward into substrates also results in configurations suitable for field emission. Well-ordered TiO₂ nanotube arrays were developed on the titanium foils in two-step anodizations. Simultaneously, arrays of sharp nanotips, which resembled the Spindt emitter arrays in appearance, also manifested themselves on the outmost surface of the foils. These nanotips were actually the remainder of the titanium foil surfaces that survived dissolution during anodization. Annealing transformed the amorphous TiO₂ nanotips into anatase crystals and further to rutile. Despite the lack of an overall large aspect ratio, the sharpness of these nanotips guaranteed sufficiently strong electric fields for electron extraction. As a result, field emission was readily obtained from the TiO₂ nanotip arrays, either before or after annealing. Photoelectron spectroscopy of the samples demonstrated that the majority of the emitted electrons came from local states in the band gap. Annealing at an appropriate temperature increased these local states and improved the field-emission capability of the samples.
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Affiliation(s)
- Jia Liang
- Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China
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286
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Cordones AA, Scheele M, Alivisatos AP, Leone SR. Probing the Interaction of Single Nanocrystals with Inorganic Capping Ligands: Time-Resolved Fluorescence from CdSe–CdS Quantum Dots Capped with Chalcogenidometalates. J Am Chem Soc 2012; 134:18366-73. [DOI: 10.1021/ja3071732] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Amy A. Cordones
- Department
of Chemistry, and ‡Department of Physics, University of California, Berkeley, California 94720, United States
- Material
Sciences Division and #Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720,
United States
| | - Marcus Scheele
- Department
of Chemistry, and ‡Department of Physics, University of California, Berkeley, California 94720, United States
- Material
Sciences Division and #Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720,
United States
| | - A. Paul Alivisatos
- Department
of Chemistry, and ‡Department of Physics, University of California, Berkeley, California 94720, United States
- Material
Sciences Division and #Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720,
United States
| | - Stephen R. Leone
- Department
of Chemistry, and ‡Department of Physics, University of California, Berkeley, California 94720, United States
- Material
Sciences Division and #Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720,
United States
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287
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ten Cate S, Schins JM, Siebbeles LDA. Origin of low sensitizing efficiency of quantum dots in organic solar cells. ACS NANO 2012; 6:8983-8988. [PMID: 22950740 DOI: 10.1021/nn303058u] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Organic semiconductors are of great interest for application in cheap and flexible solar cells. They have a typical absorption onset in the visible. Infrared light can be harvested by use of lead-chalcogenide quantum dot sensitizers. However, bulk-heterojunction solar cells with quantum-dot sensitizers are inefficient. Here we use ultrafast transient absorption and time-domain terahertz spectroscopy to show that charge localization on the quantum dot leads to enhanced coulomb attraction of its counter charge in the organic semiconductor. This localization-enhanced coulomb attraction is the fundamental cause of the poor efficiency of these photovoltaic architectures. It is of prime importance for improving solar cell efficiency to directly photogenerate spatially separated charges. This can be achieved when both charges are delocalized. Our findings provide a rationalization in the development of photovoltaic architectures that exploit quantum dots to harvest the near-infrared part of the solar spectrum more efficiently.
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Affiliation(s)
- Sybren ten Cate
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
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288
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Tang J, Liu H, Zhitomirsky D, Hoogland S, Wang X, Furukawa M, Levina L, Sargent EH. Quantum junction solar cells. NANO LETTERS 2012; 12:4889-94. [PMID: 22881834 DOI: 10.1021/nl302436r] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Colloidal quantum dot solids combine convenient solution-processing with quantum size effect tuning, offering avenues to high-efficiency multijunction cells based on a single materials synthesis and processing platform. The highest-performing colloidal quantum dot rectifying devices reported to date have relied on a junction between a quantum-tuned absorber and a bulk material (e.g., TiO(2)); however, quantum tuning of the absorber then requires complete redesign of the bulk acceptor, compromising the benefits of facile quantum tuning. Here we report rectifying junctions constructed entirely using inherently band-aligned quantum-tuned materials. Realizing these quantum junction diodes relied upon the creation of an n-type quantum dot solid having a clean bandgap. We combine stable, chemically compatible, high-performance n-type and p-type materials to create the first quantum junction solar cells. We present a family of photovoltaic devices having widely tuned bandgaps of 0.6-1.6 eV that excel where conventional quantum-to-bulk devices fail to perform. Devices having optimal single-junction bandgaps exhibit certified AM1.5 solar power conversion efficiencies of 5.4%. Control over doping in quantum solids, and the successful integration of these materials to form stable quantum junctions, offers a powerful new degree of freedom to colloidal quantum dot optoelectronics.
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Affiliation(s)
- Jiang Tang
- Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, China
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289
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In situ measurement of exciton energy in hybrid singlet-fission solar cells. Nat Commun 2012; 3:1019. [DOI: 10.1038/ncomms2012] [Citation(s) in RCA: 157] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Accepted: 07/17/2012] [Indexed: 12/23/2022] Open
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290
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Dai Q, Chen J, Lu L, Tang J, Wang W. Pulsed laser deposition of CdSe Quantum dots on Zn2SnO4 nanowires and their photovoltaic applications. NANO LETTERS 2012; 12:4187-4193. [PMID: 22823557 DOI: 10.1021/nl301761w] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In this work we report a physical deposition-based, one-step quantum dot (QD) synthesis and assembly on ternary metal oxide nanowires for photovoltaic applications. Typical solution-based synthesis of colloidal QDs for QD sensitized solar cells involves nontrivial ligand exchange processing and toxic wet chemicals, and the effect of the ligands on carrier transport has not been fully understood. In this research using pulsed laser deposition, CdSe QDs were coated on Zn(2)SnO(4) nanowires without ligand molecules, and the coverage could be controlled by adjusting the laser fluence. Growth of QDs in dense nanowire network structures was also achieved, and photovoltaic cells fabricated using this method exhibited promising device performance. This approach could be further applied for the assembly of QDs where ligand exchange is difficult and could possibly lead to reduced fabrication cost and improved device performance.
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Affiliation(s)
- Qilin Dai
- Department of Physics & Astronomy, University of Wyoming, Laramie, Wyoming 82071, USA
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291
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MacDonald BI, Martucci A, Rubanov S, Watkins SE, Mulvaney P, Jasieniak JJ. Layer-by-layer assembly of sintered CdSe(x)Te1-x nanocrystal solar cells. ACS NANO 2012; 6:5995-6004. [PMID: 22690798 DOI: 10.1021/nn3009189] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Alloying is a versatile tool for engineering the optical and electronic properties of materials. Here, we explore the use of CdTe and CdSe nanocrystals in developing sintered CdSe(x)Te(1-x) alloys as bandgap tunable, light-absorbing layers for solution-processed solar cells. Using a layer-by-layer approach, we incorporate such alloyed materials into single- and graded-composition device architectures. Nanostructured solar cells employing CdSe(x)Te(1-x) layers are found to exhibit a spectral response deeper into the IR region than bulk CdTe devices as a result of optical bowing and achieve power conversion efficiencies as high as 7.1%. The versatility of the layer-by-layer approach is highlighted through the fabrication of compositionally graded solar cells in which the [Se]:[Te] ratio is varied across the device. Each of the individual layers can be clearly resolved through cross-sectional imaging and show limited interdiffusion. Such devices demonstrate the importance of band-alignment in the development of highly efficient, nanostructured solar cells.
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Affiliation(s)
- Brandon I MacDonald
- School of Chemistry and Bio21 Institute, The University of Melbourne, Parkville, Victoria 3010, Australia
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292
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Greaney MJ, Das S, Webber DH, Bradforth SE, Brutchey RL. Improving open circuit potential in hybrid P3HT:CdSe bulk heterojunction solar cells via colloidal tert-butylthiol ligand exchange. ACS NANO 2012; 6:4222-30. [PMID: 22537193 DOI: 10.1021/nn3007509] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Organic ligands have the potential to contribute to the reduction potential, or lowest unoccupied molecular orbital (LUMO) energy, of semiconductor nanocrystals. Rationally introducing small, strongly binding, electron-donating ligands should enable improvement in the open circuit potential of hybrid organic/inorganic solar cells by raising the LUMO energy level of the nanocrystal acceptor phase and thereby increasing the energy offset from the polymer highest occupied molecular orbital (HOMO). Hybrid organic/inorganic solar cells fabricated from blends of tert-butylthiol-treated CdSe nanocrystals and poly(3-hexylthiophene) (P3HT) achieved power conversion efficiencies of 1.9%. Compared to devices made from pyridine-treated and nonligand exchanged CdSe, the thiol-treated CdSe nanocrystals are found to consistently exhibit the highest open circuit potentials with V(OC) = 0.80 V. Electrochemical determination of LUMO levels using cyclic voltammetry and spectroelectrochemistry suggest that the thiol-treated CdSe nanocrystals possess the highest lying LUMO of the three, which translates to the highest open circuit potential. Steady-state and time-resolved photoluminescence quenching experiments on P3HT:CdSe films provide insight into how the thiol-treated CdSe nanocrystals also achieve greater current densities in devices relative to pyridine-treated nanocrystals, which are thought to contain a higher density of surface traps.
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Affiliation(s)
- Matthew J Greaney
- Department of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California 90089-0744, USA
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293
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Elward JM, Hoffman J, Chakraborty A. Investigation of electron–hole correlation using explicitly correlated configuration interaction method. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.03.050] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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294
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Osedach TP, Zhao N, Andrew TL, Brown PR, Wanger DD, Strasfeld DB, Chang LY, Bawendi MG, Bulović V. Bias-stress effect in 1,2-ethanedithiol-treated PbS quantum dot field-effect transistors. ACS NANO 2012; 6:3121-7. [PMID: 22480161 DOI: 10.1021/nn3008788] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
We investigate the bias-stress effect in field-effect transistors (FETs) consisting of 1,2-ethanedithiol-treated PbS quantum dot (QD) films as charge transport layers in a top-gated configuration. The FETs exhibit ambipolar operation with typical mobilities on the order of μ(e) = 8 × 10(-3) cm(2) V(-1) s(-1) in n-channel operation and μ(h) = 1 × 10(-3) cm(2) V(-1) s(-1) in p-channel operation. When the FET is turned on in n-channel or p-channel mode, the established drain-source current rapidly decreases from its initial magnitude in a stretched exponential decay, manifesting the bias-stress effect. The choice of dielectric is found to have little effect on the characteristics of this bias-stress effect, leading us to conclude that the associated charge-trapping process originates within the QD film itself. Measurements of bias-stress-induced time-dependent decays in the drain-source current (I(DS)) are well fit to stretched exponential functions, and the time constants of these decays in n-channel and p-channel operation are found to follow thermally activated (Arrhenius) behavior. Measurements as a function of QD size reveal that the stressing process in n-channel operation is faster for QDs of a smaller diameter while stress in p-channel operation is found to be relatively invariant to QD size. Our results are consistent with a mechanism in which field-induced nanoscale morphological changes within the QD film result in screening of the applied gate field. This phenomenon is entirely recoverable, which allows us to repeatedly observe bias stress and recovery characteristics on the same device. This work elucidates aspects of charge transport in chemically treated lead chalcogenide QD films and is of relevance to ongoing investigations toward employing these films in optoelectronic devices.
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Affiliation(s)
- Timothy P Osedach
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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295
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Fu H, Tsang SW. Infrared colloidal lead chalcogenide nanocrystals: synthesis, properties, and photovoltaic applications. NANOSCALE 2012; 4:2187-201. [PMID: 22382898 DOI: 10.1039/c2nr11836j] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Simple solution phase, catalyst-free synthetic approaches that offer monodispersed, well passivated, and non-aggregated colloidal semiconductor nanocrystals have presented many research opportunities not only for fundamental science but also for technological applications. The ability to tune the electrical and optical properties of semiconductor nanocrystals by manipulating the size and shape of the crystals during the colloidal synthesis provides potential benefits to a variety of applications including photovoltaic devices, light-emitting diodes, field effect transistors, biological imaging/labeling, and more. Recent advances in the synthesis and characterization of colloidal lead chalcogenide nanocrystals and the achievements in colloidal PbS or PbSe nanocrystals solar cells have demonstrated the promising application of infrared-emitting colloidal lead chalcogenide nanocrystals in photovoltaic devices. Here, we review recent progress in the synthesis and optical properties of colloidal lead chalcogenide nanocrystals. We focus in particular upon the size- and shape-controlled synthesis of PbS, PbSe, and PbTe nanocrystals by using different precursors and various stabilizing surfactants for the growth of the colloidal nanocrystals. We also summarize recent advancements in the field of colloidal nanocrystals solar cells based on colloidal PbS and PbSe nanocrystals.
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Affiliation(s)
- Huiying Fu
- Department of Materials Science, Fudan University, Shanghai, 200433, China.
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296
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Near-Infrared Fluorescent Nanoprobes for in Vivo Optical Imaging. NANOMATERIALS 2012; 2:92-112. [PMID: 28348298 PMCID: PMC5327900 DOI: 10.3390/nano2020092] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Revised: 02/23/2012] [Accepted: 03/26/2012] [Indexed: 11/30/2022]
Abstract
Near-infrared (NIR) fluorescent probes offer advantages of high photon penetration, reduced light scattering and minimal autofluorescence from living tissues, rendering them valuable for noninvasive mapping of molecular events, assessment of therapeutic efficacy, and monitoring of disease progression in animal models. This review provides an overview of the recent development of the design and optical property of the different classes of NIR fluorescent nanoprobes associated with in vivo imaging applications.
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297
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Saunders BR. Hybrid polymer/nanoparticle solar cells: Preparation, principles and challenges. J Colloid Interface Sci 2012; 369:1-15. [DOI: 10.1016/j.jcis.2011.12.016] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Revised: 12/04/2011] [Accepted: 12/05/2011] [Indexed: 11/16/2022]
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298
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Ehrler B, Wilson MWB, Rao A, Friend RH, Greenham NC. Singlet exciton fission-sensitized infrared quantum dot solar cells. NANO LETTERS 2012; 12:1053-7. [PMID: 22257168 DOI: 10.1021/nl204297u] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We demonstrate an organic/inorganic hybrid photovoltaic device architecture that uses singlet exciton fission to permit the collection of two electrons per absorbed high-energy photon while simultaneously harvesting low-energy photons. In this solar cell, infrared photons are absorbed using lead sulfide (PbS) nanocrystals. Visible photons are absorbed in pentacene to create singlet excitons, which undergo rapid exciton fission to produce pairs of triplets. Crucially, we identify that these triplet excitons can be ionized at an organic/inorganic heterointerface. We report internal quantum efficiencies exceeding 50% and power conversion efficiencies approaching 1%. These findings suggest an alternative route to circumvent the Shockley-Queisser limit on the power conversion efficiency of single-junction solar cells.
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Affiliation(s)
- Bruno Ehrler
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 0HE, United Kingdom
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299
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Fischer SA, Crotty AM, Kilina SV, Ivanov SA, Tretiak S. Passivating ligand and solvent contributions to the electronic properties of semiconductor nanocrystals. NANOSCALE 2012; 4:904-914. [PMID: 22170563 DOI: 10.1039/c2nr11398h] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We examine in detail the impact of passivating ligands (i.e., amines, phosphines, phosphine oxides and pyridines) on the electronic and optical spectra of Cd(33)Se(33) quantum dots (QDs) using density functional theory (DFT) and time-dependent DFT (TDDFT) quantum-chemical methodologies. Most ligand orbitals are found deep inside in the valence and conduction bands of the QD, with pyridine being an exception by introducing new states close to the conduction band edge. Importantly, all ligands contribute states which are highly delocalized over both the QD surface and ligands, forming hybridized orbitals rather than ligand-localized trap states. In contrast, the states close to the band gap are delocalized over the QD atoms only and define the lower energy absorption spectra. The random detachment of one of ligands from the QD surface results in the appearance of a highly localized unoccupied state inside the energy gap of the QD. Such changes in the electronic structure are correlated with the respective QD-ligand binding energy and steric ligand-ligand interactions. Polar solvent significantly reduces both effects leading to delocalization and stabilization of the surface states. Thus, trap and surface states are substantially eliminated by the solvent. Polar solvent also blue-shifts (e.g., 0.3-0.4 eV in acetonitrile) the calculated absorption spectra. This shift increases with an increase of the dielectric constant of the solvent. We also found that the approximate single-particle Kohn-Sham (KS) approach is adequate for calculating the absorption spectra of the ligated QDs. Besides a systematic blue-shift, the KS spectra are in very good agreement with their respective counterparts calculated with the more accurate TDDFT method.
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Affiliation(s)
- Sean A Fischer
- Department of Chemistry, University of Washington, Seattle, WA 98102, USA
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300
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Buso D, Jasieniak J, Lay MDH, Schiavuta P, Scopece P, Laird J, Amenitsch H, Hill AJ, Falcaro P. Highly luminescent metal-organic frameworks through quantum dot doping. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2012; 8:80-88. [PMID: 22009888 DOI: 10.1002/smll.201100710] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Revised: 06/09/2011] [Indexed: 05/31/2023]
Abstract
The incorporation of highly luminescent core-shell quantum dots (QDs) within a metal-organic framework (MOF) is achieved through a one-pot method. Through appropriate surface functionalization, the QDs are solubilized within MOF-5 growth media. This permits the incorporation of the QDs within the evolving framework during the reaction. The resulting QD@MOF-5 composites are characterized using X-ray fluorescence, cross-sectional confocal microscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and small-angle X-ray scattering. The synergistic combination of luminescent QDs and the controlled porosity of MOF-5 in the QD@MOF-5 composites is harnessed within a prototype molecular sensor that can discriminate on the basis of molecular size.
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Affiliation(s)
- Dario Buso
- CSIRO, Materials Science and Engineering, Locked Bag 33, Clayton Sth MDC, VIC 3169, Australia
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