Novel solar cells capture audience's imagination
IFM's Gayathri Devi Rajmohan has won the People's Prize in Deakin's Three Minute Thesis competition for 2013.
New world of plasma research
Meet the team at Deakin making it happen.
Dr Xiujuan Jane Dai
+61 3 522 72427
Energy (from generation to storage)
The challenge in the field is the efficiency. To produce functional nanosemiconductors as electrodes has been the main focus for us to improve the efficiency of energy devices. A unique Plasma + Thermal technology has been developed. This system combines plasma and thermal energy to fabricate nanosemiconductors. Several plasma sources have been designed to enable different types of nano-fabrication.
Three key strategies to this approach are:
- nano-structuring (to increase surface area) including by top down (plasma etching) and bottom up (nanomaterial growth), as well as in combination with electro-chemical and chemical methods.
- element doping (to reduce band-gap and to produce multi-functional materials.)
- surface cleaning / functionalization.
Supplementing cold plasma with heat enables doping and nano-structuring of metal oxides
- D. Rubín de Celis, Z. Chen, M. M. Rahman, T. Tao, D. G. McCulloch, M. R. Field, P. R. Lamb, Y. Chen, X. J. Dai. Plasma Process. Polym. 2014, 11: 897-902.
Nitrogen doped SnO₂ polycrystalline nanostructures were produced from commercial SnO powders in a new system that combines a low-temperature plasma with heating. The method has the potential to improve the initial efficiency and the cycling performance of SnO₂ anodes in Li-ion batteries. With this system, the temperature of the SnO to SnO₂ conversion was lowered from 430 to 320°C, up to 5% of doped nitrogen was detected and a nano-scale polycrystalline structure was observed in the product. Combining heat and low-pressure plasma is a promising approach for the production and treatment of enhanced energy storage materials.
Modifying TiO₂ surface architecture by oxygen plasma to increase dye sensitized solar cell efficiency
- G. D. Rajmohan, X. J. Dai, T. Tsuzuki, P. R. Lamb, J. du Plessis, F. Huang, Y. B. Cheng, Thin Solid Films, 2013, 545: 521.
Oxygen plasma treatment of TiO₂ films has been used to improve the efficiency of dye sensitized solar cells. Both a commercial TiO₂ sample and a TiO₂ thin film synthesized by a sol-gel technique were treated using a custom built inductively coupled plasma apparatus. X-ray photoelectron spectroscopy revealed that oxygen-plasma treatment increased the number of oxygen functional groups (hydroxyl groups) and introduced some Ti³⁺ species on the surface of TiO₂.
A sample solar cell with plasma treated TiO₂ showed an overall solar-to-electricity conversion efficiency of 4.3%, about a 13% increase over untreated TiO₂. The photon conversion efficiency for the plasma treated TiO₂ was 34% higher than untreated TiO₂. This enhanced cell-performance is partly due to increased dye adsorption from an increase in surface oxygen functional groups and also may be partly due to Ti³⁺ states on the surface of TiO₂
|Absorption spectra of the desorbed dye solution of the untreated and plasma treated commercial TiO₂||I-V curves for DSSC assembled with untreated and plasma treated commercial TiO₂ electrodes.|
Clusters of alpha-LiFeO₂ nanoparticles incorporated into multi-walled carbon nanotubes: a lithium-ion battery cathode with enhanced lithium storage properties
- M.M. Rahman, A. M. Glushenkov, Z. Chen, X. J. Dai, T. Ramireddy and Y. Chen, Physical Chemistry Chemical Physics, 2013, 15: 20371-20378.
We report the preparation of a novel nanocomposite architecture of alpha-LiFeO₂-MWCNT based on clusters of alpha-LiFeO₂ nanoparticles incorporated into multiwalled carbon nanotubes (MWCNTs). The composite represents a promising cathode material for lithium-ion batteries. The preparation of the nanocomposite is achieved by combining a molten salt precipitation process and a radio frequency oxygen plasma for the first time. We demonstrate that clusters of alpha-LiFeO₂ nanoparticles incorporated into MWCNTs are capable of delivering a stable and high reversible capacity of 147 mA h g⁻¹ at 1 C after 100 cycles with the first cycle Coulombic efficiency of ~95%. The rate capability of the composite is significantly improved and its reversible capacity is measured to be 101 mA h g⁻¹ at a high current rate of 10 C. Both rate capability and cycling stability are not simply a result of introduction of functionalized MWCNTs but most likely originate from the unique composite structure of clusters of alpha-LiFeO₂ nanoparticles integrated into a network of MWCNTs. The excellent electrochemical performance of this new nanocomposite opens up new opportunities in the development of high-performance electrode materials for energy storage application using the radio frequency oxygen plasma technique.
(a) X-ray diffraction patterns of a-LiFeO₂ and a-LiFeO₂-MWCNT nanocomposite; SEM images of (b) agglomerated nanoclusters of a-LiFeO₂ (c) an individual cluster of a-LiFeO₂ nanoparticles; (d) a-LiFeO₂-MWCNT (with plasma) nanocomposite.
A vein-like nanoporous network of Nb₂O₅ with a higher lithium intercalation discharge cut-off voltage
- M.M. Rahman, R.A. Rani, A. Z. Sadek, A.S. Zoolfakar, M.R. Field, T. Ramireddy, K. Kalantar-zadeh, and Y. Chen, Journal of Materials Chemistry A, 2013, 1 (36): 11019-11025.
A novel morphology of a criss-cross vein-like nanoporous network of Nb₂O₅ produced using a simple electrochemical anodization method is presented as a superior electrode for safe lithium-ion batteries. Scanning electron microscopy (SEM) observations demonstrate that the synthesised Nb₂O₅ is made of a continuous and highly packed vein-like nanoporous network with many lateral interconnections, which provides excellent channels for the fast transfer of both Li⁺ ions and electrons. Even without surface coating or cation doping, the porous Nb₂O₅ electrode could deliver durable capacity within the operating voltage window of 1.0-3.0 V vs. Li/Li⁺, with a reversible capacity of 201 mAh g⁻¹ after 300 cycles at a current density of 0.4 A g⁻¹. At the higher discharge cut-off voltage window of 1.2-3.0 V, the reversible capacity decreased to 175 mAh g⁻¹. The first cycle Coulombic efficiency was above 94% for both operating voltage windows with a negligible capacity fading up to 300 cycles. The porous Nb₂O₅ electrode demonstrates several advantages as an anode including: (i) Improved cell safety due to a higher, V >= 1.0, discharge cut-off voltage which reduces dangerous high-temperature reactions; (ii) low level of irreversibility in the first cycle by preventing the formation of a solid electrolyte interface layer; (iii) high Coulombic efficiency due to sufficient infiltration of the electrolyte and fast diffusion of Li⁺ ions and (iv) high rate capability. Moreover, the synthesis method reports a novel smart design of nanostructured anode electrode materials capable of overcoming the existing limitations.
SEM images of the commercial Nb₂O₅ (a) and the porous network of Nb₂O₅ (b) with possible fast pathways for Li ions and electrons.
Chemically synthesized one-dimensional zinc oxide nanorods for ethanol sensing
- M. Z. Ahmad, A. Z. Sadek, K. Latham, J. Kita, R. Moos, W. Wlodarski, Sensors and Actuators B: Chemical, 2013, 187: 295.
One-dimensional (1D), single-phase (0 0 2) crystalline zinc oxide (ZnO) nanorod (NR) based conductometric sensors have been developed and investigated toward ethanol (C₂H₅OH) vapor. The ZnO NRs were chemically deposited onto conductometric transducer of alumina substrates employing a simple hydrothermal method. To facilitate the nucleation of ZnO NRs for oriented growth from the substrate, a seed layer of ZnO nanoparticles was pre-deposited employing plasma deposition technique onto the substrate containing pre-patterned interdigital electrodes (IDTs). Microcharacterization studies revealed that the NRs have a single crystal 1D structure with an average diameter of 30-50 nm. At optimum temperature range (280 to 310°C), high sensitivity, fast response and fast recovery in conjunction with a stable baseline occur.
Approach to improve dye sensitized solar cells efficiency by using plasma technology
- G. D. Rajmohan, X. J. Dai, T. Tsuzuki, ACMM 22/APMC 10/ICONN 2012: Combined conference proceedings for the 10th Asia-Pacific Micropscopy Conference, the 2012 International Conference on Nanoscience and Nanotechnology and the 22nd Australian Conference on Microscopy and Microanalysis.
The surface of TiO₂ working electrode in dye sensitized solar cells was modified using O₂ plasma. The cell efficiency was increased by 13%. Surface characterization revealed the changes in the surface charge state and the chemical composition after the plasma treatment
Controlled surface modification of boron nitride nanotubes
- X. J. Dai, Y. Chen, Z. Chen, P. R. Lamb, L. H. Li, J. du Plessis, D. G McCulloch, X. Wang, Nanotechnology. 2011; 22: 245301.
Controlled surface modification of boron nitride nanotubes has been achieved by gentle plasma treatment. Firstly, it was shown that an amorphous surface layer found on the outside of the nanotubes can be removed without damaging the nanotube structure. Secondly, it was shown that an oxygen plasma creates nitrogen vacancies that then allow oxygen atoms to be successfully substituted onto the surface of BNNTs. The percentage of oxygen atoms can be controlled by changing the input plasma energy and by the Ar plasma pre-treatment time. Finally, it has been demonstrated that nitrogen functional groups can be introduced onto the surface of BNNTs using an N2 + H2 plasma. The N2 + H2 plasma also created nitrogen vacancies, some of which led to surface functionalization while some underwent oxygen healing.
(a) amorphous layer (~5-10 nm) in an untreated BNNT; (b) after O₂ plasma treatment, showing removal of the a-BN layer without damage to the nanotubes.
Anodization of Ti thin film deposited on ITO
- A.Z. Sadek, H. Zheng, K. Latham, W. Wlodarski, K. Kalantar-zadeh, Langmuir.2009; 25(1): 509.
We have investigated several key aspects for the self-organization of nanotubes in RF sputtered titanium (Ti) thin films formed by the anodization process in fluoride-ion-containing neutral electrolytes. Ti films were deposited on indium tin oxide (ITO) glass substrates at room temperature and 300°C, and then anodized. The films were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-vis spectrometry before and after anodization. It was observed that anodization of high temperature deposited films resulted in nanotube type structures with diameters in the range of 10-45 nm for an applied voltage of 5-20 V. In addition, the anatase form of TiO₂ is formed during the anodization process which is also confirmed using photocurrent measurements. However, the anodization of room temperature deposited Ti films resulted in irregular pores or holes.
High temperature anodized WO₃ nanoplatelet films for photosensitive devices
- A. Z. Sadek, H. Zheng, M. Breedon, V. Bansal, S. K. Bhargava, K. Latham, P. Spizzirri, W. Wlodarski, K. Kalantar-zadeh, Langmuir.2009; 25(16): 9545.
Anodization at elevated temperatures in nitric acid has been used for the production of highly porous and thick tungsten trioxide nanostructured films for photosensitive device applications. The anodization process resulted in platelet crystals with thicknesses of 20-60 nm and lengths of 100-1000 nm. Maximum thicknesses of 2.4 μm were obtained after 4 h of anodization at 20 V. X-ray diffraction analysis revealed that the as-prepared anodized samples contain predominantly hydrated tungstite phases depending on voltage, while films annealed at 400°C for 4 h are predominantly orthorhombic WO₃ phase. Photocurrent measurements revealed that the current density of the 2.4 μm nanostructured anodized film was 6 times larger than the nonanodized films. Dye-sensitized solar cells developed using these films produced 0.33 V and 0.65 mA/cm² in open- and short-circuit conditions.
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