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

Lead Research Organisation: University of Liverpool
Department Name: Physics

Abstract

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.

Planned Impact

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.

Publications

10 25 50
 
Description CAMREG Flexi Fund projects
Amount £44,240 (GBP)
Organisation University of Edinburgh 
Sector Academic/University
Country United Kingdom
Start 08/2018 
End 07/2019
 
Description EPSRC Capital Award emphasising support for Early Career Researchers
Amount £225,000 (GBP)
Funding ID EP/S017623/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2018 
End 04/2020
 
Description Studentship - Industry Top-Up
Amount £10,000 (GBP)
Funding ID 148952 
Organisation NSG Nippon Sheet Glass Pilkington 
Sector Private
Country Japan
Start 10/2017 
End 10/2021
 
Description Brine Solar 
Organisation Exigosolar Ltd
Country United Kingdom 
Sector Private 
PI Contribution Providing expertise on processing CdTe solar cells with non-toxic salts
Collaborator Contribution Expertise in recovery of salts from wast salt-water brines
Impact Joint application Climate-KIC Accelerator application
Start Year 2016
 
Description NSG partnership - Band alignments and Silver based transparent conductors 
Organisation NSG Nippon Sheet Glass Pilkington
Country Japan 
Sector Private 
PI Contribution Awarded NPF PhD studentship on band alignments. Work will focus on new Sb2Se3 solar cell platform developed by my research team. Additionally I have suggested the concept to develop a Silver based TCO for inorganic PV which is now an ongoing project with NSG Ltd
Collaborator Contribution £10K contribution to studentship.Provided bespoke coated glass.
Impact Papers in preparation
Start Year 2017
 
Description Article for Physics World 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Article on materials development for solar cells "The Generation Game" written for Physics World magazine
Year(s) Of Engagement Activity 2018
 
Description Hi-Py workshops 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact Laurie Phillips involved in running "Hi-Py" introduction to the Python programming language workshops. These have been initially targeted at UoL undergrads but have been further extended to the local community.
This is an ongoing series with monthly workshops of around 50+ attendees.
Year(s) Of Engagement Activity 2016,2017
URL http://www.hipy.uk/
 
Description IOP Northwest Talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Invited talk on photovoltaics for Institute of Physics north west branch
Year(s) Of Engagement Activity 2018
 
Description Mining/PV news article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I wrote an article on deep sea mining and PV for the conversation website which was then featured on the independent website and in the i-newspaper.
Year(s) Of Engagement Activity 2017
URL http://www.independent.co.uk/news/science/deep-sea-mining-could-help-develop-mass-solar-energy-is-it...
 
Description Presentation at Merseyside sceince teachers conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Gave talk on solar energy to local science teachers and discussed current research focus and ways this could be implemented in teaching.
Year(s) Of Engagement Activity 2017
 
Description Tate Liverpool presentation 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Talk at Tate Liverpool's "Made from light" event
Year(s) Of Engagement Activity 2018
 
Description University of Liverpool Podcast 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I was interviewed for the University of Liverpool Podcast discuss my work
Year(s) Of Engagement Activity 2017
URL https://www.online.liverpool.ac.uk/resource/tofu-solar-panels-vs-big-business