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Andrew Watt

Dr Andrew Watt
RCUK Academic Fellow

Department of Materials
University of Oxford
16 Parks Road
Oxford OX1 3PH
UK

Tel: +44 1865 613456 (Room 352.10.45)
Tel: +44 1865 273700 (switchboard)
Fax: +44 1865 273789 (general fax)

Solar Energy Materials Initiative

Summary of Interests

Dr Andrew Watt is a Research Councils of the United Kingdom Academic Fellow in the Department of Materials at the University of Oxford. He leads a group of 14 scientists interested in taking energy materials research from the synthesis of new nanomaterials through to the fabrication, characterization and application of devices. 

Current Research Projects

Coatings for enhanced light capture in solar cells
Dr. J. Moghal, Dr. A.A.R. Watt, Dr. J. Best*, Dr. M. Gardener*, Dr. G. Wakefield*
This work focuses on the design and development of anti-reflectance coatings for a variety of solar cell architectures. A solution processed nanoparticle coating has been developed which increases transmission by at least 6% and reduce reflection per surface to <0.5%. We integrate these optical layers into solar cell devices and quantify performance enhancement in terms of reflectance and power conversion efficiency. (*Oxford Advanced Surfaces)

Low cost and toxicity solar cells
C. Smallwood, L. Droessler, E.X. Zou, Dr. A.A.R. Watt, Professor C.R.M. Grovenor. Dr. C. Blandford*
The leading second generation thin film solar cells are made of copper indium gallium diselenide and cadmium telluride. Significant market penetration of these systems is hampered by their toxicity and use of expensive rare earth metals. There is growing need to develop new second generation thin film photovoltaic materials which are robust, low energy cost, lower toxicity and recyclable. This project develops new visible light absorbing metal oxide thin films using sol-gel chemistry. 

Enhancing the efficiency of thin film solar cells using optical confinement
M. Wincott, A. Powell, Dr. H.E. Assender, Dr. A.A.R. Watt, Dr. J.M. Smith
Thin film solar cells offer an inexpensive means to generate clean energy, but current efficiencies are limited to around five percent, about three times lower than commercial polycrystalline silicon cells. One of the main reasons behind the low efficiency is that a tension exists between the desire to absorb as much as possible of the incident light, in which case the optical path length should be thick (at least several hundred nanometres), and the desire to extract the photogenerated charge carriers efficiently from the cell, in which case the exciton transport path length should be short (no more than a few tens of nanometers). Most attempts to solve this problem involve using a thick cell, and focusing the advanced aspects of cell design on building in some means for ensuring a short transport path length. Here we take the opposite viewpoint; that the optical path can be elongated for a given cell geometry by the use of wave guiding and cavitation, thereby reducing the burden placed on the transport related features of the device. This new project involves the design, fabrication, and testing of devices that explore this theme by employing inexpensive approaches to encourage light to propagate in the plane of the film.

Energy harvesting in biomimetic systems
Dr. B.W. Lovett*, Dr. A.A.R.Watt
Light is converted to chemical energy with extremely high efficiency in photosynthetic systems. Part of the reason for this is that light can create exciton states in protein antenna structures, and these antenae are arranged such that the exciton energy can be transferred to a specific site quickly and efficiently. In my work, I aim to understand this efficiency as the result of an interplay between exciton trasnfer interactions and environmental coupling to phonons. In particular, I aim to design synthetic systems that can mimic biological efficiencies, thus providing a route to optimized solar cells. (*Heriot-Watt University)

Multi band-gap metal oxide photovoltaic materials
L. Droessler, Dr. A.A.R. Watt, Dr. H.E. Assender
There is growing need to develop new second generation thin film photovoltaic materials which are robust, low energy cost, low toxicity and recyclable. The project examines visible light absorbing metal oxide semiconductors in all inorganic multi-junction thin film solar cells. A number of vaccum processing methods are being trialled suitable for high-throughput processing including reactive evaporation and sputtering.

Advanced optoelectronic characterisation of solar cells
J. Holder, Dr. A.A.R. Watt, Dr. H.E. Assender
Understanding the optoelectronic nature of solar cells is crucial to optimising fabrication processes and enhancing device efficiency. This project utilises a range of characterisation techniques to extract device parameters such as charge carrier mobility, material interface potential, and trap state density in an effort to better understand the underlying physics of solar cells. A number of techniques are available within the lab including impedance spectroscopy, time of flight, electroabsorption and Hall Effect.

Vacuum deposition of polymer photovoltaic devices
P. Kovacik, Dr. A.A.R. Watt, Dr. H.E. Assender
Conjugated polymers have demonstrated enhanced properties in terms of light absorption and hole-transport, and in combination with fullerene electron-acceptors the highest power conversion efficiency organic solar cells. However, the use of solvents substantially limits the complexity of the devices as the coating solutions interfere with already deposited layers. Vacuum deposition is a solvent-free process, advantageous for its simplicity and ability to evaporate unlimited number of layers with well controlled thickness and composition. Although some polymer materials have been deposited by physical vapour deposition techniques, there have not been any attempts to deposit conjugated polymers in the same way. This project will involves the comparison of evaporated polymer-based photovoltaic devices with those deposited by solution casting, and development of the vacuum deposition processesElectroabsoprtion of nanocomposite photovoltaic materials

Roll-to-roll processing of organic electronics
Dr G.A.W. Abbas, Z. Ding, Dr. H.E. Assender
Electronics components that can be manufactured using roll-to-roll processing offer the possibility of lower cost devices as well as those that might be mechanically flexible in use.  Roll-to-roll (R2R) processing, using a flexible substrate (typically a polymer film) allows for cheap production of many components very rapidly, with low energy requirements.  Key areas of exploitation of this technology include flexible displays, but there is also a wealth of lower-cost applications. Tagging and tracking of fast moving consumer goods is an example technology that truly exploit the very low-cost nature of the production and in which the manufacturing is closely linked to the manufacturing routes currently exploited for e.g. packaging technologies.  This project seeks to exploit the existing industrialised technology of vacuum R2R processing, widely used for example in the packaging industry, to develop the manufacture of very low cost organic field-effect transistor (OFET)-based devices and circuits.  This manufacturing route, like solvent based systems, is cheap and provides flexible product, and we can exploit high electrical mobility molecular semiconductors. Additional advantages of the solvent-free vacuum processes include: a) likely enhanced web-speed, b) integration with vacuum-based metal deposition for conducting channels, and metal or ceramic deposition for barrier layers and possible interfacial modification, and c) the ability to deposit multiple thin layers to build up device structures without solvent interactions with underlying layers.  The project will exploit our existing R2R web processing facility to explore the principal manufacturing challenges to R2R vacuum production of OFET devices: 1) selection and adaptation of materials to vacuum deposition integrated with design of suitable circuitry, 2) patterning of the semiconductor and insulator layers to allow the formation of circuit connections between devices and 3) reliability of manufacture to be able to produce arrays of multiple transistors for circuits.  It will allow us to explore and develop the deposition of molecular semiconductor and dielectric materials and then the subsequent reliability and thermo-mechanical resilience of the resulting product such that it might need to withstand, for example, during a lamination process.

Excitons in semiconductor nano-heterostructures
E. Tyrrell, S. Fairclough, Dr. A.A.R. Watt, Dr. J.M. Smith
Semiconductor nanocrystals with strong optical transitions are becoming increasingly important in a wide range of applications in fields as diverse as medicine, renewable energy, and telecommunications. In nanocrystals made from a single constituent material choosing the size also determines other important optical properties, such as the luminescence lifetime and linewidth. However it is also possible to grow heterostructures of different materials, to explore different quantum confinement geometries which modify the behaviour in both quantitative and qualitative fashion. In this project we focus on a particular design of nanocrystal - the 'type II' nano heterostructure - in which electrons and holes are spatially separated in different core and shell regions, all within a few-nanometres diameter crystal! These nanocrystals are particularly attractive for use in solar cells, and in optical amplifiers and lasers. The project involves both experimental and theoretical approaches to determine the design rules and optical properties of these materials.

Solution processed transparent conductors
E.X. Zou, Dr. A.A.R. Watt, Professor C.R.M. Grovenor
Transparent conductive electrodes (TCE) have been developed with a combination of high optical transparency and electrical conductivity. In the field of organic photovoltaics there is a need to develop TCE which are electronically tailored to enhance charge extraction and transport. Development of alternatives to the current leading TCE indium tin oxide is also crucial for electronic, environmental and economic reasons. Aluminium doped zinc oxide (AZO) is one promising alternative due to its abundance, ease of manufacturing and excellent electronic properties. This project uses simple and cost effective sol-gel methods to fabricate doped metal oxide thin films on a variety of substrates. The TCE is then used in bulk heterojunction nanocomposite solar cells.

10 public active projects

Research Publications

  1. "Vacuum-Deposited Planar Heterojunction Polymer Solar Cells", ACS Applied Materials and Interfaces, Peter Kovacik, Giuseppe Sforazzini, Andrew G. Cook,Shawn M. Willis,Patrick S. Grant, Hazel E. Assender,and Andrew A. R. Watt, http://pubs.acs.org/doi/abs/10.1021/am1008985
  2. "Colloidal Synthesis of Lead Oxide Nanocrystal for Photovoltaics" Christopher A. Cattley, Alexandros Stavrinadis, Richar  Beal, Jonathan Moghal, Andrew G. Cook, Patrick S. Grant, Jason M. Smith, Hazel Assender and Andrew A. R. Watt CHEMICAL COMMUNICATIONS, 2010, 46, 2802 – 2804.
  3. “SnS/PbS nanocrystal heterojunction photovoltaics” Alexandros Stavrinadis, Jason M Smith, Christopher A Cattley, Andrew G Cook, Patrick S Grant and Andrew A R Watt.  NANOTECHNOLOGY 21(18):185202, 2010.
  4. "The Molecular Structure of Polymer−Fullerene Composite Solar Cells and Its Influence on Device Performance" Richard M. Beal, Alexandros Stavrinadis, Jamie H. Warner, Jason M. Smith, Hazel E. Assender and Andrew A. R. Watt MACROMOLECULES, 2010, 43 (5), pp 2343–2348
  5. "Ultrahigh secondary electron emission of carbon nanotubes" Luo, J, Warner, JH, Feng, CQ Yao, YG Jin, Z Wang, HL Pan, CF Wang, S Yang, LJ Li, Y Zhang, J Watt, AAR Peng, LM Zhu, J Briggs, GAD. Appl. Phys. Lett. 96, 213113 (2010)
  6. Watt, AAR; Bothma, JP; Meredith, P. 2009. The supramolecular structure of melanin. SOFT MATTER 5 (19):3754-3760
  7. Keeble, DJ; Thomsen, EA; Stavrinadis, A; Samuel, IDW; Smith, JM; Watt, AAR. 2009. Paramagnetic Point Defects and Charge Carriers in PbS and CdS Nanocrystal Polymer Composites. JOURNAL OF PHYSICAL CHEMISTRY C 113 (40):17306-17312
  8. Stavrinadis, Alexandros; Xu, Sen; Warner, Jamie H; Hutchison, John L; Smith, Jason M; Watt, Andrew A R. 2009. Superstructures of PbS nanocrystals in a conjugated polymer and the aligning role of oxidation. NANOTECHNOLOGY 20 (44):445608.
  9. Cao, HQ; Wang, GZ; Warner, JH; Watt, AAR. 2008. Amino-acid-assisted synthesis and size-dependent magnetic behaviors of hematite nanocubes. APPLIED PHYSICS LETTERS 92 (1), art.no.-013110.
  10. Xiang, JH; Cao, HQ; Wu, QZ; Zhang, SC; Zhang, XR; Watt, AAR. 2008. L-cysteine-assisted synthesis and optical properties of Ag2S nanospheres. JOURNAL OF PHYSICAL CHEMISTRY C 112 (10):3580-3584.
  11. Warner, JH; Watt, AAR; Ge, L; Porfyrakis, K; Akachi, T; Okimoto, H; Ito, Y; Ardavan, A; Montanari, B; Jefferson, JH; Harrison, NM; Shinohara, H; Briggs, GAD. 2008. Dynamics of paramagnetic metallofullerenes in carbon nanotube peapods. NANO LETTERS 8 (4):1005-1010.
  12. Wu, QZ; Cao, HQ; Luan, QY; Zhang, JY; Wang, Z; Warner, JH; Watt, AAR. 2008. Biomolecule-assisted synthesis of water-soluble silver nanoparticles and their biomedical applications. INORGANIC CHEMISTRY 47 (13):5882-5888.
  13. Buitelaar, MR; Fransson, J; Cantone, AL; Smith, CG; Anderson, D; Jones, GAC; Ardavan, A; Khlobystov, AN; Watt, AAR; Porfyrakis, K; Briggs, GAD. 2008. Pauli spin blockade in carbon nanotube double quantum dots. PHYSICAL REVIEW B 77 (24), art.no.-245439.
  14. Warner, JH; Ito, Y; Zaka, M; Ge, L; Akachi, T; Okimoto, H; Porfyrakis, K; Watt, AAR; Shinohara, H; Briggs, GAD. 2008. Rotating fullerene chains in carbon nanopeapods. NANO LETTERS 8 (8):2328-2335.
  15. Stavrinadis, A; Beal, R; Smith, JM; Assender, HE; Watt, AAR. 2008. Direct formation of PbS nanorods in a conjugated polymer. ADVANCED MATERIALS

Projects Available

Biomimetic Energy Storage Devices
Dr Andrew Watt

Melanins are macromolecules found throughout the biosphere. Eumelanin is found in skin pigment and act as a photoprotectant and has been implicated in the development of deadly malignant melanoma. This project will seek to understand the optoelectronic properties of melanin using materials science techniques and fabricate supercapacitor structures using squid ink courtesy of the Japanese fishing industry. The project will involve, fabrication of melanin composite films, fabrication of supercapacitor devices, measurement of impedance and electrochemical properties and some physicochemical characterization eg XRD, SEM, XPS, TEM.

Also see homepages: Andrew Watt

Metal Oxide Photovoltaics
Dr Andrew Watt

The leading second generation thin film solar cells are made of copper indium gallium diselenide and cadmium telluride. Significant market penetration of these systems is hampered by their toxicity and use of expensive rare earth metals. There is growing need to develop new second generation thin film photovoltaic materials which are robust, low energy cost, lower toxicity and recyclable. The project will examine visible light absorbing metal oxide semiconductors which we have developed and proven to work effectively in solar cell devices. The project will involve, deposition of thin films visible light absorbing ternary metal oxide, fabrication of solar cell devices, power conversion efficiency and spectral response measurements and some physicochemical characterization eg XRD, SEM, XPS, TEM. There is a commercial license associated with this project and close industrial collaboration and further IP generation is expected.

Also see homepages: Andrew Watt

Engineering excitons in semiconductor nanocrystals
Dr Jason Smith and Dr Andrew Watt

The ability to grow heterostructured semiconductor nanocrystals using wet chemical techniques opens up a plethora of new possibilities for engineering their optical and electrical properties. For instance (i) in type II heterostructures, the electron and hole that form the ‘exciton’ are separated spatially, so that optical gain can be generated; and (ii) alloyed structures have recently been grown in which luminescence blinking is absent – a discovery that may hold the key to developing nanocrystal-based LEDs, sensors, and even quantum optical devices. The aim of this project will be to investigate the excitonic behaviour of heterostructured and alloyed nanocrystals. In particular, low temperature spectroscopy of single nanocrystals will be used to gain information free from inhomogeneous and thermal broadening. Experimental results will be compared with theory developed in-house. Applicants interested in the synthesis of alloyed and heterostructured nanocrystals will also be considered.

Also see homepages: Jason Smith Andrew Watt

Reactive Metal Nanoparticles for Batteries
Dr Andrew Watt

Recently we discovered a new method for producing highly reactive metal nanoparticles (eg aluminum, lithium) in large volumes and under environmentally friendly conditions. The process overcomes the major barriers for using reactive metals as materials in batteries or hydrogen generators; (1) there is no surface oxide to prevent reaction, and (2) the nanoparticles are so small that once the reaction has taken place all metal has been reacted so there is no waste. The objective of this project is to utilize Aluminum’s superior energy density to weight ratio, zero emissions potential and minimal toxicity to produce a hydrocarbon replacement fuel source.

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Metal-Organic-Semiconductor Nano-composites Transparent Conductors
Dr Andrew Watt

Transparent conductors are part of life from iPod touch screens to solar cells. Current technologies utilise doped metal oxides, however the constituent materials and processing method are expensive and not applicable to a wide range of substrates (eg plastics). This project will involve the synthesis of percolated networks of metal nano-particles in a porous hosts, thin film processing on a variety of substrates, conductivity and mobility measurements along with some physicochemical characterization eg XRD, SEM, XPS, TEM. There is IP generated within the research group associated with this project and close industrial collaboration and further IP generation is expected.

Also see homepages: Andrew Watt

Also see a full listing of New projects available within the Department of Materials.