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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

Tel: +44 1865 613456 (Room 352.10.45)
Tel: +44 1865 273777 (reception)
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 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).