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Andrew Watt

Professor Andrew Watt
Associate Professor of Materials

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

Andrew leads a group of 14 scientists on energy materials research from the synthesis of new nanomaterials through to the fabrication, characterization and application of devices. The group has considerable experience in the synthesis of nanomaterials, thin film device fabrication, optoelectronic materials characterisation and advanced transmission electron microscopy techniques. Recent highlights include, the demonstration of vacuum thermal evaporation of conducting polymers for solar cells, high resolution TEM imaging of polymer lamellae in bulk heterojunction photovoltaic devices,  and the initial demonstration of a SnS nanocrystal heterojunction thin film photovoltaic devices.

Current Research Projects

Vacuum deposition of polymer photovoltaic devices
N. Klein, 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

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.

2 public active projects

Research Publications

Visit http://scholar.google.co.uk/citations?user=X3qNsJkAAAAJ&hl=en for full publication list.

Key publications:

1. Low temperature phase selective synthesis of Cu 2 ZnSnS 4 quantum dots CA Cattley et al. Chemical Communications 49, p3745 (2013).

2. Morphology control in co-evaporated bulk heterojunction solar cells P Kovacik et al. Solar Energy Materials and Solar Cells 117, p22 (2013).

3. The transitional heterojunction behavior of PbS/ZnO colloidal quantum dot solar cells SM Willis, Nano letters 12, p1522-1526 (2012).

4. The Molecular Structure of Polymer− Fullerene Composite Solar Cells and Its Influence on Device Performance, RM Beal et al. Macromolecules 43, p2343 (2010).

5. Vacuum-deposited planar heterojunction polymer solar cells, P Kovacik et al. ACS applied materials & interfaces 3, p11 (2010).

6. SnS/PbS nanocrystal heterojunction photovoltaics A Stavrinadis. Nanotechnology 21, p185202 (2010).

7. The supramolecular structure of melanin. AAR Watt et al. Soft Matter 5, p3754 (2009).

8. Lead sulfide nanocrystal: conducting polymer solar cells, AAR Watt et al. Journal of Physics D: Applied Physics 38 , p2006 (2005).

Projects Available

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.

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