Overcoming the grain size limit to Voc in sustainable photovoltaics
Lead Research Organisation:
University of Liverpool
Department Name: Physics
Abstract
Solar electricity based on wafer silicon is a mature technology that is in widespread use. Although it is getting cheaper due to mass production in China, the international market is still driven by government subsidies. Alternative 'thin film' materials are the best chance of competition, but they have three problems:
a) their voltages are lower than expected due to the small size of the crystal grains in them (several millionths of a meter typically),
b) the materials presently used for thin film solar cells contain rare elements that will pose supply issues as the PV industry expands by several hundred fold over the next 40 years, and
c) production methods must become cheaper and more effective in order to compete in the global market
We will test a new method to make solar cells that promises to overcome all of these limitations. We will work on the archetypal earth abundant semiconductor Cu2ZnSn(S,Se)4 (CZTSS). Solar cells made from it suffer from the typical problems: It underperforms on voltage and has very small crystal grains. It is also difficult to make since it is prone to lose sulphur and selenium (the most successful research labs resort to complex methods involving nanoparticles and dangerous reducing solvents). The efficiency has been limited to 12% for some years now, and this is preventing CZTSS from becoming a production technology.
In this project we will test an alternative method to grow CZTSS. We will explore the possibility of growing large grains of CZTSS on cheap metal sheet with small grains -we expect this could become a workable production route. We will make some hundreds of solar cells to test the hypotheses.
Overall the idea has the potential to increase the efficiency of CZTSS from 12% to 16%, or even higher, making it feasible to open up a pathway for new PV products. A technological lead in this area could give the UK the opportunity to grab back a share of the expanding global PV business.
a) their voltages are lower than expected due to the small size of the crystal grains in them (several millionths of a meter typically),
b) the materials presently used for thin film solar cells contain rare elements that will pose supply issues as the PV industry expands by several hundred fold over the next 40 years, and
c) production methods must become cheaper and more effective in order to compete in the global market
We will test a new method to make solar cells that promises to overcome all of these limitations. We will work on the archetypal earth abundant semiconductor Cu2ZnSn(S,Se)4 (CZTSS). Solar cells made from it suffer from the typical problems: It underperforms on voltage and has very small crystal grains. It is also difficult to make since it is prone to lose sulphur and selenium (the most successful research labs resort to complex methods involving nanoparticles and dangerous reducing solvents). The efficiency has been limited to 12% for some years now, and this is preventing CZTSS from becoming a production technology.
In this project we will test an alternative method to grow CZTSS. We will explore the possibility of growing large grains of CZTSS on cheap metal sheet with small grains -we expect this could become a workable production route. We will make some hundreds of solar cells to test the hypotheses.
Overall the idea has the potential to increase the efficiency of CZTSS from 12% to 16%, or even higher, making it feasible to open up a pathway for new PV products. A technological lead in this area could give the UK the opportunity to grab back a share of the expanding global PV business.
Planned Impact
1. Who will benefit:
- Society in general - from CO2 reductions.
The report of the 40th Session of the International Panel on Climate Change (01 Nov 2014) states: There is a 95% chance that climate change is anthropogenic - continued emissions will increase the likelihood of severe irreversible impacts. It recommends substantial emissions reductions over the next few decades and near zero emissions of CO2 by the end of the century. www.ipcc.ch
- UK and EU industrial capacity - by recovering a share of the growing market for PV from the Far East
- Traditional industries in the UK- by diversifying to high value added products from large volume cheap products such as galvanized sheet.
- New and existing solar electricity module producers - will gain from new manufacturing opportunities.
- Research community for earth abundant PV - gain a new approach to creating viable PV device technologies.
- PV materials and packaging supply chain - gains from increase in production
- PV installation industries - from increased deployment resulting from low cost manufacture.
2. How the benefits will arise:
Increasing the UK market share. Market disruption is the only way to win back PV manufacturing from Far Eastern dominance. We propose a radical shift in technology that could re-invent the industry and allow the UK and Europe to reclaim a market share in a growing industry from China and Taiwan who have led massive expansion of conventional technology.
Transformation of traditional industries to a value added model. e.g. the UK manufactures coated steel sheet at 200,000,000 m2 per annum at <10p/m2, but there is presently no direct manufacturing industry for thin film solar cells - that would sell at £50 - 100 £/m2. Our innovations will a) create a pathway for the transformation to high added value using existing industrial expertise and b) create a new market for low cost sheet and foil materials in high tech manufacture
PV expansion without subsidies. A new route to a revised mass market for PV will eliminate the dependency of the international market on subsidies hence allowing a natural market - led expansion of solar electricity.
Meeting CO2 targets. Expansion of from GWp to TWp production levels, will have a substantial contribution to CO2 targets and the economy. In simple terms, the production of 1 TW of solar electricity will take out the equivalent of ten typical fossil fuel power stations that produce CO2
Training of an essential workforce for advanced industry. We will link the project to the EPSRC Centre for Doctoral Training in New and Sustainable PV - there is an excellent fit. In particular a CDT student at Liverpool, Mr Peter Yates, will work on transmission electron microscope characterisation of the crystal quality of the layers and PV devices. He started in October 2014 and so his post will outlast this research project. We will seek an additional student from the CDT, although this will of course require the approval of the Management Board.
- Society in general - from CO2 reductions.
The report of the 40th Session of the International Panel on Climate Change (01 Nov 2014) states: There is a 95% chance that climate change is anthropogenic - continued emissions will increase the likelihood of severe irreversible impacts. It recommends substantial emissions reductions over the next few decades and near zero emissions of CO2 by the end of the century. www.ipcc.ch
- UK and EU industrial capacity - by recovering a share of the growing market for PV from the Far East
- Traditional industries in the UK- by diversifying to high value added products from large volume cheap products such as galvanized sheet.
- New and existing solar electricity module producers - will gain from new manufacturing opportunities.
- Research community for earth abundant PV - gain a new approach to creating viable PV device technologies.
- PV materials and packaging supply chain - gains from increase in production
- PV installation industries - from increased deployment resulting from low cost manufacture.
2. How the benefits will arise:
Increasing the UK market share. Market disruption is the only way to win back PV manufacturing from Far Eastern dominance. We propose a radical shift in technology that could re-invent the industry and allow the UK and Europe to reclaim a market share in a growing industry from China and Taiwan who have led massive expansion of conventional technology.
Transformation of traditional industries to a value added model. e.g. the UK manufactures coated steel sheet at 200,000,000 m2 per annum at <10p/m2, but there is presently no direct manufacturing industry for thin film solar cells - that would sell at £50 - 100 £/m2. Our innovations will a) create a pathway for the transformation to high added value using existing industrial expertise and b) create a new market for low cost sheet and foil materials in high tech manufacture
PV expansion without subsidies. A new route to a revised mass market for PV will eliminate the dependency of the international market on subsidies hence allowing a natural market - led expansion of solar electricity.
Meeting CO2 targets. Expansion of from GWp to TWp production levels, will have a substantial contribution to CO2 targets and the economy. In simple terms, the production of 1 TW of solar electricity will take out the equivalent of ten typical fossil fuel power stations that produce CO2
Training of an essential workforce for advanced industry. We will link the project to the EPSRC Centre for Doctoral Training in New and Sustainable PV - there is an excellent fit. In particular a CDT student at Liverpool, Mr Peter Yates, will work on transmission electron microscope characterisation of the crystal quality of the layers and PV devices. He started in October 2014 and so his post will outlast this research project. We will seek an additional student from the CDT, although this will of course require the approval of the Management Board.
Organisations
People |
ORCID iD |
Ken Durose (Principal Investigator) |
Publications
Birkett M
(2018)
Band gap temperature-dependence of close-space sublimation grown Sb2Se3 by photo-reflectance
in APL Materials
Hobson T
(2020)
Defect properties of Sb2Se3 thin film solar cells and bulk crystals
in Applied Physics Letters
Hobson T
(2021)
Protocols for the Miller indexing of Sb2Se3 and a non-x-ray method of orienting its single crystals
in Materials Science in Semiconductor Processing
Hobson T
(2020)
Vegard Relation and Raman Band Reference Data Generated from Bulk Crystals of Kesterite-Phase Composition Series Cu 2 ZnSnS 4 x Se 4-4 x (CZTSSe, 0 = x = 1)
in Crystal Growth & Design
Hutter O
(2018)
6.6% efficient antimony selenide solar cells using grain structure control and an organic contact layer
in Solar Energy Materials and Solar Cells
Keeble DJ
(2021)
Identification of lead vacancy defects in lead halide perovskites.
in Nature communications
Peccerillo E
(2018)
Copper-antimony and copper-bismuth chalcogenides-Research opportunities and review for solar photovoltaics
in MRS Energy & Sustainability
Phillips L
(2019)
Current Enhancement via a TiO2 Window Layer for CSS Sb2Se3 Solar Cells: Performance Limits and High V oc
in IEEE Journal of Photovoltaics
Shiel H
(2020)
Natural Band Alignments and Band Offsets of Sb 2 Se 3 Solar Cells
in ACS Applied Energy Materials
Shiel H
(2019)
Chemical etching of Sb 2 Se 3 solar cells: surface chemistry and back contact behaviour
in Journal of Physics: Energy
Shiel H
(2021)
Band alignment of Sb2O3 and Sb2Se3
in Journal of Applied Physics
Description | Sb2Se3 has been developed as a thin film solar cell material. We have evaluated its fundamental properties from single crystals grown in our lab, and have also developed prototype PV devices from it up to about 6%. |
Exploitation Route | This is the starting point for evolution of Sb2Se3 into a viable material for solar photovoltaics. |
Sectors | Electronics Energy |
Description | 1/ The project generated fundamental data for use in R&D of thin film solar cell materials, namely CZTSSe, copper zinc tin sulpho-selenide. This is a solid solution series for which the S/Se ratio is important since it controls the semiconductor bandgap and the lattice parameter of the material. The bandgap has a direct impact on the solar cell efficiency and so it is important to be able to measure the composition accurately. In this work we grew large grained crystal samples across the whole composition range. These crystals were then used to produce an accurate calibration graph of the lattice parameter vs composition. 2/ We evaluated the feasibility of forming large grained CZTSe films by liquid phase epitaxy in an attempt to increase the peformance of photovoltaic devices made from them. The outcome was that the method was not successful and we ascribed this to the inability of the method to go slowly enough to avoid a peritectic reaction. 3/ Given the outcome of (2) also investigated single crystals of Sb2se3, another emerging solar energy material. Again we were able to determine fundamental data including new information about the Raman bands and the conductivity due to native defects and extrinsic dopants. |
Sector | Energy |
Impact Types | Economic |
Description | MRS Fall Meeting 2017 O Hutter |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Presentation of research results entitled "Growth and Characterisation of Highly Crystalline CZTSSe" at the Fall MRS Conf November 2017. |
Year(s) Of Engagement Activity | 2018 |
URL | http://www.mrs.org/fall2017 |
Description | RS Conference London 2018 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | Presentation of a research talk "Growth and Characterisation of Crystalline Cu2ZnSn(S,Se)4 (CZTSSe) for Fundamental Studies" at the Royal Society of Chemistry's Jan 2018 conference Next Generation Materials for Solar Photovoltaics. The outcome was to disseminate the results of the RCUK funded research. |
Year(s) Of Engagement Activity | 2018 |
URL | http://www.rsc.org/events/detail/28000/next-generation-materials-for-solar-photovoltaics-2018 |