Jacek Jasieniak | Monash University (original) (raw)

Papers by Jacek Jasieniak

Journal of the American Chemical Society, Mar 8, 2017

In this work, we present a combined experimental and theoretical analysis of two-component ligand... more In this work, we present a combined experimental and theoretical analysis of two-component ligand shells passivating CdSe quantum dots. Using nuclear magnetic resonance spectroscopy, we first show that exposing oleate-capped quantum dots to primary carboxylic acids results in a one-for-one exchange that preserves the overall ligand surface concentration. Exposure to straight-chain acids leads to a binary ligand shell that behaves as an ideal mixture and that has a composition matching the overall acid composition of the dispersion. In the case of branched-chain acids, the exchange is restricted to about 25% of the original ligands. Based on molecular dynamics simulations, we argue that this behavior reflects the more favorable packing of oleates compared to branched carboxylates on the (100) facets of CdSe quantum dots.

Chemistry of Materials, 2010

... JJ acknowledges the CSIRO OCE Postdoctoral Fellowship scheme for funding. We thank Sven Fjast... more ... JJ acknowledges the CSIRO OCE Postdoctoral Fellowship scheme for funding. We thank Sven Fjastad for help with the ICP-AES data, Carl Braybrook for help with the mass spectrometry, and Matthias Haeussler for help with GPC. ...

Journal of Physical Chemistry B, 2005

High quality CdSe nanocrystals have been prepared using elemental selenium as the chalcogenide pr... more High quality CdSe nanocrystals have been prepared using elemental selenium as the chalcogenide precursor dispersed in 1-octadecene (ODE). The conditions used to prepare the Se precursor were found to be critical for successful nanocrystal synthesis. Systematic titration of the Se precursor solution with tri-n-octylphosphine (TOP) allowed the Se reactivity to be tuned and the final particle size to be controlled. Band-edge and surface related emission were observed for samples prepared in the presence and absence of added TOP. In the absence of a selenium passivant, the crystal structure of CdSe nanocrystals could be altered from zinc blende to wurtzite by the addition of bis(2,2,4-trimethylpentyl)phosphinic acid (TMPPA).

Advanced Energy Materials, 2013

ABSTRACT It is demonstrated that a combination of microsecond transient photocurrent measurements... more ABSTRACT It is demonstrated that a combination of microsecond transient photocurrent measurements and film morphology characterization can be used to identify a charge-carrier blocking layer within polymer:fullerene bulk-heterojunction solar cells. Solution-processed molybdenum oxide (s-MoOx) interlayers are used to control the morphology of the bulk-heterojunction. By selecting either a low- or high-temperature annealing (70 °C or 150 °C) for the s-MoOx layer, a well-performing device is fabricated with an ideally interconnected, high-efficiency morphology, or a device is fabricated in which the fullerene phase segregates near the hole extracting contact preventing efficient charge extraction. By probing the photocurrent dynamics of these two contrasting model systems as a function of excitation voltage and light intensity, the optoelectronic responses of the solar cells are correlated with the vertical phase composition of the polymer:fullerene active layer, which is known from dynamic secondary-ion mass spectroscopy (DSIMS). Numerical simulations are used to verify and understand the experimental results. The result is a method to detect poor morphologies in operating organic solar cells.

Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications IX, 2010

abstract In the last years inorganic semiconductor (particularly CdSe and CdS) quantum dots (QDs)... more abstract In the last years inorganic semiconductor (particularly CdSe and CdS) quantum dots (QDs) have received great attention for their important optical properties. The possibility to tune the emission wavelength, together with their high fluorescence quantum efficiency and photostability, can be exploited in photonic and optoelectronic technological applications. The design of DFB devices, based on QDs as active optical material, leads to the realization of compact laser systems. In this work we explore the use of an inorganic/ ...

NATO Science for Peace and Security Series B: Physics and Biophysics, 2010

... Alexander Heisterkamp Biophotonics Group Department of Biomedical Optics Hollerithallee 8 D-3... more ... Alexander Heisterkamp Biophotonics Group Department of Biomedical Optics Hollerithallee 8 D-30419 Hannover, Germany Tel.:++ 49 511 2788-484; Fax.:++ 49 511 2788-100 E-mail: a ... Melanie Schwingel Universität Karlsruhe (TH) Zoologisches Institut I Haid-und-Neu-Str. ...

2010 Conference on Optoelectronic and Microelectronic Materials and Devices, 2010

We report on the use of sol-gel-processed amorphous oxides based on a (ZnxSny)Oz composition to d... more We report on the use of sol-gel-processed amorphous oxides based on a (ZnxSny)Oz composition to develop thin-film transistors (TFTs) with electron mobility exceeding 1 cm2/Vs and high on/off ratios (&gt;;106). These devices are aided by a high K dielectric developed by CSIRO, which enables reduced operating voltages to be achieved.

Journal of the American Chemical Society, Jan 14, 2007

We report a protocol for manipulating the surface composition of CdSe nanocrystals. By combining ... more We report a protocol for manipulating the surface composition of CdSe nanocrystals. By combining the successive ion layer adhesion and reaction (SILAR) method developed by Li et al. J. Am. Chem. Soc. 2003, 125, 12567 with a phosphine-free selenium precursor, the surface stoichiometry of CdSe can be tunably altered from Cd- to Se-rich. By changing the overall surface stoichiometry, we demonstrate ligand binding to specific surface sites. Tertiary phosphines produce a dramatic enhancement in photoluminescence quantum yield of CdSe particles with Se-rich surfaces but have little effect on Cd-rich surfaces. Unpassivated selenium surface sites are also shown to be a cause of the photobrightening behavior of CdSe nanocrystals.

Chemistry of Materials, 2015

ABSTRACT

ACS Applied Materials & Interfaces, 2014

Solution processing provides a versatile and inexpensive means to prepare functional materials wi... more Solution processing provides a versatile and inexpensive means to prepare functional materials with specifically designed properties. The current challenge is to mimic the structural, optical, and/or chemical properties of thin films fabricated by vacuum-based techniques using solution-based approaches. In this work we focus on ZnO to show that thin films grown using a simple, aqueous-based, chemical bath deposition (CBD) method can mimic the properties of sputtered coatings, provided that the kinetic and thermodynamic reaction parameters are carefully tuned. The role of these parameters toward growing highly oriented and dense ZnO thin films is fully elucidated through detailed microscopic and spectroscopic investigations. The prepared samples exhibit bulk-like optical properties, are intrinsic in their electronic characteristics, and possess negligible organic contaminants, especially when compared to ZnO layers deposited by sol-gel or from nanocrystal inks. The efficacy of our CBD-grown ZnO thin films is demonstrated through the effective replacement of sputtered ZnO buffer layers within high efficiency solution processed Cu2ZnSnS4xSe4(1-x) solar cells.

ACS Nano, 2014

Plasmonic metal oxide nanocrystals bridge the optoelectronic gap between semiconductors and metal... more Plasmonic metal oxide nanocrystals bridge the optoelectronic gap between semiconductors and metals. In this study, we report a facile, non-injection synthesis of ZnO nanocrystals doped with Al, Ga, or In. The reaction readily permits dopant/zinc atomic ratios of over 15%, is amenable to high precursor concentrations (0.2 M and greater), and provides high reaction yields (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;90%). The resulting colloidal dispersions exhibit high transparency in the visible spectrum and a wavelength-tunable infrared absorption, which arises from a dopant-induced surface plasmon resonance. Through a detailed investigation of reaction parameters, the reaction mechanism is fully characterized and correlated to the optical properties of the synthesized nanocrystals. The distinctive optical features of these doped nanocrystals are shown to be readily harnessed within thin films that are suitable for optoelectronic applications.

Highly luminescent CdSe-ZnS core-shell nanocrystals are utilized as dopant within ZrO 2 and HfO 2... more Highly luminescent CdSe-ZnS core-shell nanocrystals are utilized as dopant within ZrO 2 and HfO 2 hybrid sol-gel matrices. The emission properties of these hybrid materials are studied upon one-and two-photon excitation by fs laser pulses. Under these optical pumping regimes, lowthreshold amplified stimulated emission is observed. Furthermore, the optical gain characteristics of these QD hybrid materials within 1D and 2D distributed feedback laser architectures are explored.

ABSTRACT The effect of doping and porosity of the n-type ZnO layer on the performance of solution... more ABSTRACT The effect of doping and porosity of the n-type ZnO layer on the performance of solution-processed, sintered p-CdTe/n-ZnO nanocrystal photovoltaic (PV) devices is investigated. Amorphous sol-gel ZnO is found to be the best candidate with overall energy conversion efficiencies above 8% obtained if the ZnO is also indium doped. We demonstrate that when such PV devices are left under forward bias (in dark or light), the device efficiency values are raised to at least 9.8%, due to a substantially increased open-circuit voltage and fill-factor. This drastic enhancement is attributed to improved band alignment at the ITO/CdTe interface. The forward-bias treatment is slowly reversed over a period of days to weeks on standing under open circuit conditions, but is readily restored with further voltage treatment. The moderate processing conditions and high efficiency of such devices demonstrate that nanocrystal-based systems are a promising technology for photovoltaics.

ABSTRACT The chemical origin of the UV-enhanced conductivity of ZnO nanoparticle thin-films is st... more ABSTRACT The chemical origin of the UV-enhanced conductivity of ZnO nanoparticle thin-films is studied. Improved electrical properties are shown for organic photovoltaics, thin-film transistors and diodes utilizing UV-illuminated nanoparticle ZnO films. Using impedance spectroscopy we find that as prepared ZnO nanoparticle films exhibit clear signatures of grain boundary conduction, which is eliminated following UV illumination in nitrogen atmosphere. Exposure to ambient air is found to increase the grain boundary resistance to its original state after oxygen, then water, adsorb to the surface. Gas chromatography mass spectrometry confirms that, as with bulk ZnO, the UV illumination process results in desorption of oxygen as well as oxidation of carbonaceous species at the surface. Loss of photo-generated holes through this oxidative process results in excess electrons in the ZnO, which in turn produces the observed electronic changes.