J.Jasieniak, B.MacDonald, S.Watkins, P. Mulvaney
Nano Letters 11, 2856-64 (2011); (DOI: 10.1021/nl201282v)
Scientists at the Nanoscience Laboratory and CSIRO have published the first paper using wet chemical nanocrystals as a means to fabricate efficient photovoltaic devices. The devices incorporate a p-CdTe layer prepared by spin coating CdTe semiconductor nanocrystals or quantum dots and a colloidal ZnO n-type layer. The p-n heterojunction cells typically exhibit > 8% IPCE and champion devices have already exceeded 10%. The work has already led to a Du Pont Young Innovator Award for PhD student Brandon MacDonald and was highlighted at the recent MRS Meeting in San Francisco. The work is now in press in the premier nanoscience journal Nano Letters. One of the key investigators, Dr Jacek Jasieniak, who has just been awarded a Fulbright Fellowship to examine solar commercialisation in the US, says the new methods clearly show there are many materials and technologies which could be help lower the cost of PV electricity. The solution based processing technology has been jointly patented by the University of Melbourne and CSIRO.
IP: Contact Sabina Zahirovic at Melbourne Ventures (03 8344 3067, sabina.zahirovic@unimelb.edu.au)
Nano Letters dx.doi.org/10.1021/nl201282v
Jacek Jasieniak,*,†,§ Brandon I. MacDonald,‡,†,§ Scott E. Watkins,† and Paul Mulvaney*,‡
†CSIRO, Materials Science and Engineering, Bayview Avenue, Clayton, Victoria, 3168, Australia
‡School of Chemistry and Bio21 Institute, The University of Melbourne, Parkville, Victoria, 3010, Australia
Abstract:
Solar cells made by high temperature and vacuum processes from inorganic semiconductors are at a perceived cost disadvantage when compared with solution-processed systems such as organic and dye-sensitized solar cells. We demonstrate that totally solution processable solar cells can be fabricated from inorganic nanocrystal inks in air at temperature as low as 300 C. Focusing on a CdTe/ZnO thin-fi lm system, we report solar cells that achieve power conversion effi ciencies of 6.9% with greater than 90% internal quantum effi ciency. In our approach, nanocrystals are deposited from solution in a layer-by-layer process. Chemical and thermal treatments between layers induce large scale grain formation, turning the 4 nm CdTe particles into pinhole-free fi lms with an optimized average crystallite size of ∼ 70 nm. Through capacitance voltage measurements we demonstrate that the CdTe layer is fully depleted which enables the charge carrier collection to be maximized.
KEYWORDS: Solar cell, nanocrystal, CdTe, sintered, layer-by-layer, solution processed
DOI: 10.1002/adfm.201100432 Adv. Funct. Mater. 2011, 21, 2580–2586
Anthony J. Morfa , Alexandre M. Nardes , Sean E. Shaheen , Nikos Kopidakis , and Jao van de Lagemaat *
Dr. A. J. Morfa
School of Chemistry & Bio21 Institute
University of Melbourne
Parkville 3010, Victoria, Australia
Dr. A. M. Nardes , Prof. S. E. Shaheen , Dr. N. Kopidakis ,
Dr. J. van de Lagemaat
National Renewable Energy Laboratory
Golden, Colorado, 80401, USA
E-mail: jao.vandelagemaat@nrel.gov
Prof. S. E. Shaheen
Department of Physics and Astronomy
University of Denver
Denver, Colorado 80210, USA
Abstract:
The charge-collection dynamics in poly(3-hexylthiophene:[6,6]-phenyl- C 61 -butyric acid methyl ester (P3HT:PCBM) bulk heterojunctions are studiedin thick ( > 1 μ m) devices using time-of-fl ight measurements and external quantum-effi ciency measurements. The devices show Schottky-diode behavior with a large fi eld-free region in the device. Consequently, electron transport occurs by diffusion in the bulk of the active layer. At high applied biases where the depletion region spans the entire active layer, normal time-of-fl ight transients are observed from which the electron mobility can be determined. Here, the electron mobility follows Poole–Frenkel behavior as a function of fi eld. At lower applied biases, where the depletion region only spans a small portion of the active layer, due to a high density of dark holes, the recombination kinetics follow a fi rst-order rate law with a rate constant about two orders of magnitude lower than that predicted by Langevin recombination.
Scientists at the University of Melbourne have carried out the first true quantum measurements in living cells. The paper has just appeared in Nature Nanotechnology.
"Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells"
by L. P. McGuinness, Y. Yan, A. Stacey, D. A. Simpson, L. T. Hall, D. Maclaurin, S. Prawer, P. Mulvaney, J. Wrachtrup, F. Caruso, R. E. Scholten and L. C. L. Hollenberg Nat. Nanotech. 6, 358 (2011).
Abstract
Fluorescent particles are routinely used to probe biological processes. The quantum properties of single spins within fluorescent particles have been explored in the field of nanoscale magnetometry, but not yet in biological environments. Here, we demonstrate optically detected magnetic resonance of individual fluorescent nanodiamond nitrogen-vacancy centres inside living human HeLa cells, and measure their location, orientation, spin levels and spin coherence times with nanoscale precision. Quantum coherence was measured through Rabi and spin-echo sequences over long (>10 h) periods, and orientation was tracked with effective 18 angular precision over acquisition times of 89 ms. The quantum spin levels served as fingerprints, allowing individual centres with identical fluorescence to be identified and tracked simultaneously.Furthermore, monitoring decoherence rates in response to changes in the local environment may provide new information about intracellular processes. The experiments reported here demonstrate the viability of controlled single spin probes for nanomagnetometry in biological systems, opening up a host of new possibilities for quantum-based imaging in the life sciences.
JOURNAL OF APPLIED PHYSICS 109, 094305 doi: :10.1063/1.3579442
Benjamin Mashford, Julia Baldauf, Tich-Lam Nguyen, Alison M. Funston, and Paul Mulvaney
Abstract:
Semiconductor quantum dots (QDs) are used to dope wide-bandgap chalogenide glasses via sol-gel processing. Such chalcogenides enhance surface passivation of the quantum dots, as evidenced by the increased PL emissions of both core and core shell species used, while a ZnO glass leads to irreversible oxidation of the embedded quantum dots. The embedded QDs are photostable.
J. Mater. Chem., 2011, 21, 10823,DOI: 10.1039/c1jm10531k
Edin Nuhiji,*a Franc¸ois G. Amar,*b Hongxia Wang,a Nolene Byrne,a Tich-Lam Nguyenc and Tong Lina
Abstract:
Emission spectra from microdroplets doped with CdSe/ZnS quantum dots (QDs) have been recorded
on superhydrophobic coatings (water contact angle > 170). Whispering gallery modes (WGMs) with
Q-factors as high as 4.0 103 were discernible. Excitation parameters for optimal microdroplet WGM
response illumination and acquisition are also presented. Fluorescent QDs provide a robust WGM
reporting mechanism under extreme continuous wave microdroplet excitation (465.5 mW) for periods
greater than 15 minutes. In this format droplets could be optically tuned on demand using
combinations of QDs. Ionic liquid QD-doped droplet emission was found to be spectrally stable:
a >75% improvement in WGM blue-shift was recorded (due to droplet evaporation) compared to
QD-doped glycerol/water droplet emission. Theoretical analysis of emission spectra confirmed the
observed emission response curves correspond to Mie theory suggesting the droplets are extremely close
to spherical on the surface. This versatile liquid resonator system has direct implications in high
performance room-temperature laser development, telecommunications research and lab-on-a-chip
based diagnostics.
dx.doi.org/10.1021/la200166r | Langmuir 2011, 27, 6026–6030
Rico F. Tabor,†,^ Anthony J. Morfa,‡,§ Franz Grieser,§,^ Derek Y. C. Chan,||,^,# and Raymond R. Dagastine*,†,^
†Department of Chemical and Biomolecular Engineering, University of Melbourne, Parkville 3010, Australia
‡Bio21 Institute, University of Melbourne, Parkville 3010, Australia
§School of Chemistry, University of Melbourne, Parkville 3010, Australia
)Department of Applied Maths and Statistics, University of Melbourne, Parkville 3010, Australia
^Particulate Fluids Processing Centre, University of Melbourne, Parkville 3010, Australia
#Faculty of Life and Social Sciences, Swinburne University of Technology, Hawthorne, VIC 3122, Australia
ABSTRACT:
Atomic force microscopy, contact-angle, and spectroscopic ellipsometry
measurements were employed to investigate the presence and properties of
gold oxide on the surface of gold metal. It was found that, in agreement with
available literature, unoxidized gold surfaces were hydrophobic, whereas oxidation
rendered the surface highly hydrophilic. The oxide could be removed with ethanol
or base but appeared to be stable over long periods in water or salt solutions
between pH 3 and 7. After oxidation, the oxide layer thickness, determined using
ellipsometry, was consistent with an approximate monolayer of AuO bonds at
the gold surface. The presence of gold oxide was found to alter significantly the
electrical double-layer characteristics of the gold surface below pH 6 and may
explain the apparent inconsistencies in observed force behavior where gold is
employed as well as aiding in design of future microfluidic systems which
incorporate gold as a coating.
Lab on a Chip, 2011, 11, pages 921-928
DOI: 10.1039/c0lc00481b
Adam F. Chrimes, Aminuddin A. Kayani, Khashayar Khoshmanesh, Paul R. Stoddart, Paul Mulvaney, Arnan Mitchella and Kourosh Kalantar-zadeha.
A microfluidic dielectrophoresis platform consisting of curved microelectrodes was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a quartz substrate, which has insignificant Raman response, and integrated with a microfluidic channel that was imprinted in poly-dimethylsiloxane (PDMS). We will show that this novel integrated system can be efficiently used for the determination of suspended particle types and the direct mapping of their spatial concentrations. We will also illustrate the system’s unique advantages over conventional optical systems. Nanoparticles of tungsten trioxide (WO3) and polystyrene were used in the investigations, as they are Raman active and can be homogeneously suspended in water.
Physical Chemistry Chemical Physics, issue 13 2011, pages 5576-5578.
DOI: 10.1039/c0cp02494e
Sarah Jaber, Matthias Karg, Anthony Morfa and Paul Mulvaney
2D arrays of Au–PNIPAM core–shell nanocrystals were fabricated using convective deposition and spin-coating. The particle density and ordering were studied by AFM. Annealing at 700 1C removes the polymer shell, while retaining a monolayer of well-separated gold nanoparticles. The surface plasmon modes of the colloid monolayers could be measured by spectroscopic ellipsometry
The Journal of Physical Chemistry C, 2011, 115, pages 327-324,
DOI: 10.1021/jp104953z
Guoliang Zhen, Benjamin W. Muir, Bradford A. Moffat, Peter Harbour,
Keith S. Murray, Boujemaa Moubaraki, Kiyonori Suzuki, Ian Madsen,
Nicki Agron-Olshina, Lynne Waddington, Paul Mulvaney, and Patrick G. Hartley
A modified method for the production of cubic and spherical superparamagnetic nanoparticles is presented. Cubic nanoparticles can be made that are highly monodisperse down to a diameter of 8 nm. A detailed study is presented of the physical properties of these nanoparticles using high-resolution transmission electron microscopy analysis, X-ray powder diffraction, superconducting quantum interference device measurements, and relaxivity measurements performed in a magnetic resonance imaging scanner. It is found that cubic iron oxide nanoparticles have a higher degree of crystallinity and relaxivity (four times higher) than their spherical counterparts. These novel cubic iron oxide nanoparticles show great promise for use in biomedical imaging applications.