Capacitance spectroscopy led process innovations to improve VOC in CdTe thin film solar cells

An alternative solar cell technology: Cadmium telluride (CdTe) solar cells offer an alternative to the current market leading Silicon based photovoltaic (PV) modules. CdTe solar cells have lower materials costs and generate less CO2 during production that Si. These modules are now in mass production and are already one of the lowest cost-per-watt solar technologies. Their continued development is however being limited by a failure to improve the generated voltage. This limit needs to be overcome in order reduce the cost per watt of power generation from solar and help end the need for a subsidised PV market. This fellowship seeks to identify a way to overcome this limitation.

A new methodology: The standard way to improve solar cell performance is through empirical process developments, optimising deposition conditions and techniques. This fellowship seeks to develop a different approach by using powerful capacitance spectroscopy techniques to identify routes to new process innovations. Capacitance spectroscopy allows electrically active defects, which are the cause of the voltage loss in CdTe solar cells, to be identified. By monitoring the number and position of these defects, linked to cell production and performance, we can identify both their source and their impact. This allows the key defects which most harm cell performance to be determined and thus process innovations to eliminate them can be developed. Through this physics-led approach to cell production we can overcome the voltage limitation in CdTe solar cells.

Wider impact: Whilst this project focuses on CdTe solar cells, the methodology established will have wider implications. There are a number of other solar cell technologies that have similar limitations and can benefit from the application of the techniques developed during this fellowship. The work undertaken in this project will benefit an entire generation of solar cells.

The research team: The fellowship applicant Dr Jon Major will lead the research team working on the project. Dr Major has over ten years' experience working with CdTe solar cells and is one of the country's leading young PV researchers. The project will be carried out at the University of Liverpool's Stephenson Institute for Renewable Energy, a cross-disciplinary research centre working on numerous aspects of renewable energy.

This fellowship proposal has three key aims;
- Overcome the voltage limitation in CdTe solar cells.
- Establish a capacitance spectroscopy led approach to solar cell development.
- Accelerate the career progression of one of the UK's leading young PV researchers.

PV market growth - The current solar photovoltaics (PV) market is driven by subsidies. In order to maintain the rapid market growth of PV further cost reductions are required. The work proposed in this fellowship aims to improve the performance and thereby lower the cost of PV power generation from CdTe solar cells. Furthermore, it seeks to establish a new capacitance spectroscopy led methodology by which other solar cell technologies may likewise be improved. PV power generation is widely expected to be a major low-carbon technology in the future energy mix and thus key to achieving the governmental target of 15% renewable energy generation by 2020. This work contributes to the fundamental knowledge and development of PV and thus to the continued growth of the PV market. This will have impact on a number of areas;

Environmental: The need to move to low-carbon renewable energy sources is beyond dispute. The long term impacts of climate change are liable to devastating and to severely impact everyone on the planet. By moving to renewable low-carbon energy sources, such as PV, the environmental impact of power generation can be minimised. In order to achieve this, the cost reduction of PV to ensure it is competitive with other sources of power generation is essential.This fellowship targets a reduction in the cost of PV via increased cell performance.

Energy security: A shift towards a more PV based power generation model will enhance the UK's energy security. PV allows power to be generated domestically without the reliance on oil or gas from international sources.

UK and global economy: It has been estimated that around 48 jobs are created in the manufacturing and installation sectors of the PV industry for every MW of installed capacity (EPIA - "Solar Generation V", Sep 08). Continued growth of the PV market will create new jobs and ensure future UK and global economic prosperity.

Industrial manufacture: The UK has particular strength in the PV supply chain through NSG ltd (formerly Pilkington), who are the world's largest supplier of coated glass for PV. Further market growth will increase the demand. Solar cell module manufacturers will also naturally benefit as a result of this work and two of the largest CdTe manufacturers, First Solar and Calyxo GmbH, are involved with the project.

UK skills base: This fellowship will train skilled postdoctoral and PhD researchers thereby contributing to the UK knowledge and skills base. These researchers are anticipated to contribute to the future knowledge economy through leading roles in academia or industry.

Engagement with research: Renewable energy is a highly emotive subject for a large number of people and as a result PV research generates widespread interest outside the scientific community. This fellowship will demonstrate a route whereby fundamental research may inform and improve large scale industrial production. This will help to inspire the next generation of scientists by showing a clear link between fundamental materials science and real world impact. This work will also help maintain the high public approval of PV and renewable energy, which impacts on future energy policy.