Hot swap

The deployment of large-scale solar energy utilities could be made more economically viable with photovoltaic (PV) materials that are being developed in Oxford.

The technology has been developed by researchers at ISIS Innovation, Oxford University’s technology transfer company.

Andrew Watt, from Oxford’s Department of Materials, explained that the new ISIS photovoltaic system is based on visible-light-absorbing metal oxides commonly used as pigments in paints.

‘Current PV technologies are costly, around $0.25/kilowatt hour compared to oil, gas, coal, nuclear and wind, which come in around $0.05/kilowatt,’ he said. ‘The reason for this is partly associated with the cost of manufacture and partly the materials used.’

Scientists have looked for a number of years for replacements for silicon, which is commonly used in photovoltaic systems.

Watt said a number of thin-film inorganic systems are commercially available. Those include CIGS (copper indium gallium diselenide) or Cadmium Tellurium devices, which offer good solar-power conversion efficiencies. However, the systems rely on rare elements and contain highly toxic materials.

‘There is now a resurgence looking at cheaper and more environmentally friendly semiconductor technologies that do not use Cadmium or expensive metals such as Indium, which has a projected supply of 20 years,’ he added.

Watt said the challenge for the ISIS team in its new photovoltaic system was changing the semiconducting nature of its material for photovoltaic devices. To accomplish this, he explained that the team had to reconfigure the crystal structure of the photovoltaic system, adjust its chemistry and create a new doping process.

Otherwise the design of the device is similar to existing technologies, which include a metal anode-cathode with p- and n-type semiconductors in between them.

Watt added that the inorganic thin-film photovoltaic system is not yet ready to compete with silicon on a performance level. ‘At the moment, our power conversion efficiencies are lower than standard silicon devices,’ he said. ‘We hope to push efficiencies to between 6-8 per cent in the next three years.’

Yet Watt said it offers other advantages. ‘The real advantage comes from cost of processing,’ he added. ‘A ten-fold decrease in efficiency makes devices 100 times cheaper. So if space is not an issue the material is ideal. Think solar farms in desert area converting sunlight to electricity to hydrogen for distribution around the world.’

The ISIS team points out that its system has good photochemical stability relative to other low-cost organic systems. It is compatible with existing industrial coating methods and the system’s metal oxides offer aesthetic advantages such as transparency and the possibility to create a variety of colours.

Stuart Wilkinson, project manager with Isis Innovation, said the technology is patented and the group hopes to attract investors and development partners.

‘We aim to develop a suite of materials with bespoke semiconducting and light-absorbing properties,’ he added. ‘Then using a device modelling package we can optimise the device’s design and generate the highest efficiency devices possible.’

Siobhan Wagner