Gettering of impurities in silicon: delivering quantitative understanding to improve photovoltaics
Lead Research Organisation:
University of Warwick
Department Name: WMG
Abstract
Photovoltaics have the potential to supply all the world's energy needs. The market for photovoltaics is dominated by cells made from crystalline silicon, which account for more than 80% of today's production. Whilst other technologies are being researched, silicon's abundance, chemical stability, density, band gap and non-toxic nature mean that is certain to play a leading role in at least the medium term. More than half of bulk silicon solar cells are fabricated from multicrystalline silicon (mc-Si) wafers. Although mc-Si photovoltaics have lower efficiencies than their single-crystal counterparts, their substantially lower production costs means the technologies have equal commercial viability at present. Mc-Si is produced by casting, often using a low grade feedstock, and is consequently packed with extended defects (dislocations, grain boundaries and precipitates) and transition metal impurity point defects. Recombination of photogenerated charge carriers at such defects is a major reason for the reduced efficiency of mc-Si cells. Gettering processes are routinely used either to redistribute the defects or remove them from the material. However, such processes are not completely effective. One of the major reasons for this is that the interaction between defects prevents them being gettered. This project aims to further the fundamental understanding of defect interactions in mc-Si. The thermodynamics of interactions between transition metals (particularly iron) and extended defects (particularly dislocations and oxide precipitates) will be studied experimentally. Passivation of key extended defects will also be investigated. The fundamental knowledge obtained should allow the development of new or modified gettering processes with the ultimate aim of facilitating the use of dirtier (hence cheaper) feedstocks for silicon photovoltaics.
Planned Impact
There will be many beneficiaries in addition to those in the sizeable academic community in this field. It is clear that the £40bn solar cell industry - most of which is focused on silicon - will benefit directly by being able to produce more efficient products at a reduced cost. The UK has substantial activity in this area (including Sharp and PV Crystalox Solar) and so this research will provide economic benefits to UK industry. The scientific outcomes in the project will also be directly relevant to the £200bn semiconductor industry. Gettering in the production of silicon-based integrated circuits is ubiquitous and the fundamental knowledge gained will result in higher yield production of more reliable electronic devices.
It is generally accepted that global warming is now occurring and although its current extent and future impact are unclear, many scientists believe that a global crisis is a real possibility. Photovoltaics are able to supply all the world's energy needs with minimal carbon emissions. Whilst solar technologies other than silicon are being researched, silicon's abundance, chemical stability, density, band gap, and non-toxic nature mean that it is the only photovoltaic material currently available which is certain to be able to fulfil all our long-term energy needs. At present unsubsidised silicon photovoltaic technologies are marginally economically uncompetitive compared to electricity generated from fossil fuels. The improved understanding arising from my research has the potential to deliver substantial improvements in gettering processes in multicrystalline silicon, allowing more efficient solar cells to be produced from cheaper feedstocks. The impact of this would be more cost-effective solar cell modules which are better able to compete with conventional electricity sources. It is not unrealistic to think that this could be achieved in the next five years. The mass uptake of improved products would result in vastly reduced greenhouse gas emissions and may slow down, or even reverse, global warming. I feel my topic of research has the potential to have major impact in the field and in society.
It is generally accepted that global warming is now occurring and although its current extent and future impact are unclear, many scientists believe that a global crisis is a real possibility. Photovoltaics are able to supply all the world's energy needs with minimal carbon emissions. Whilst solar technologies other than silicon are being researched, silicon's abundance, chemical stability, density, band gap, and non-toxic nature mean that it is the only photovoltaic material currently available which is certain to be able to fulfil all our long-term energy needs. At present unsubsidised silicon photovoltaic technologies are marginally economically uncompetitive compared to electricity generated from fossil fuels. The improved understanding arising from my research has the potential to deliver substantial improvements in gettering processes in multicrystalline silicon, allowing more efficient solar cells to be produced from cheaper feedstocks. The impact of this would be more cost-effective solar cell modules which are better able to compete with conventional electricity sources. It is not unrealistic to think that this could be achieved in the next five years. The mass uptake of improved products would result in vastly reduced greenhouse gas emissions and may slow down, or even reverse, global warming. I feel my topic of research has the potential to have major impact in the field and in society.
People |
ORCID iD |
| John Murphy (Principal Investigator) |
Publications
Wratten A
(2023)
Hafnium oxide: A thin film dielectric with controllable etch resistance for semiconductor device fabrication
in AIP Advances
Zhu Y
(2021)
Electrical Characterization of Thermally Activated Defects in n -Type Float-Zone Silicon
in IEEE Journal of Photovoltaics
Grant N
(2021)
Gallium-Doped Silicon for High-Efficiency Commercial Passivated Emitter and Rear Solar Cells
in Solar RRL
Grant N
(2020)
Lifetime instabilities in gallium doped monocrystalline PERC silicon solar cells
in Solar Energy Materials and Solar Cells
Pointon A
(2020)
Sub-2 cm/s passivation of silicon surfaces by aprotic solutions
in Applied Physics Letters
Al-Amin M
(2019)
Iodine-Ethanol Surface Passivation for Measurement of Millisecond Carrier Lifetimes in Silicon Wafers with Different Crystallographic Orientations
in physica status solidi (a)
Hooper IR
(2019)
High efficiency photomodulators for millimeter wave and THz radiation.
in Scientific reports
Murphy J
(2019)
Minority carrier lifetime in indium doped silicon for photovoltaics
in Progress in Photovoltaics: Research and Applications
Mullins J
(2018)
Thermally activated defects in float zone silicon: Effect of nitrogen on the introduction of deep level states
in Journal of Applied Physics
Grant N
(2017)
Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications
in IEEE Journal of Photovoltaics
Al-Amin M
(2017)
Low-Temperature Saw Damage Gettering to Improve Minority Carrier Lifetime in Multicrystalline Silicon
in physica status solidi (RRL) - Rapid Research Letters
Al-Amin M
(2017)
Combining Low-Temperature Gettering With Phosphorus Diffusion Gettering for Improved Multicrystalline Silicon
in IEEE Journal of Photovoltaics
Al-Amin M
(2017)
Passivation Effects on Low-Temperature Gettering in Multicrystalline Silicon
in IEEE Journal of Photovoltaics
Al-Amin M
(2016)
Increasing minority carrier lifetime in as-grown multicrystalline silicon by low temperature internal gettering
in Journal of Applied Physics
Murphy J
(2015)
The effect of oxide precipitates on minority carrier lifetime in n -type silicon
in Journal of Applied Physics
Al-Amin M
(2015)
Low Temperature Internal Gettering of Bulk Defects in Silicon Photovoltaic Materials
in Solid State Phenomena
Leonard S
(2015)
Evidence for an iron-hydrogen complex in p-type silicon
in Applied Physics Letters
Rougieux F
(2015)
Influence of Annealing and Bulk Hydrogenation on Lifetime-Limiting Defects in Nitrogen-Doped Floating Zone Silicon
in IEEE Journal of Photovoltaics
Murphy J
(2014)
Competitive gettering of iron in silicon photovoltaics: Oxide precipitates versus phosphorus diffusion
in Journal of Applied Physics
Murphy J
(2014)
Minority carrier lifetime in silicon photovoltaics: The effect of oxygen precipitation
in Solar Energy Materials and Solar Cells
| Description | The project furthered the understanding of the fundamental science of the interaction between defects in silicon materials which are used in >90% of solar cells. This includes details of how transition metal impurities interact with extended defects, such as a precipitates, dislocations and grain boundaries. The project developed new low temperature processes for improve minority carrier lifetime in multicrystalline silicon materials, including internal gettering and external gettering to saw damage at the wafer surfaces. |
| Exploitation Route | The processes developed could be used by the silicon solar cell industry to develop lower cost photovoltaic modules. The processes are compatible with low quality (hence low cost) feedstocks which unless improved are currently discarded. Thus, the processes could be used to increase production yields and to improve efficiencies of solar cells. The overall impact will be most cost-effective solar cells. |
| Sectors | Energy |
| Description | Dark matter and the ultimate performance limit of semiconductor silicon |
| Amount | £222,147 (GBP) |
| Funding ID | RPG-2020-377 |
| Organisation | The Leverhulme Trust |
| Sector | Charity/Non Profit |
| Country | United Kingdom |
| Start | 04/2021 |
| End | 03/2024 |
| Description | EPSRC Global Challenges Research Fund (GCRF) |
| Amount | £342,394 (GBP) |
| Funding ID | EP/P511079/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | |
| End | 03/2017 |
| Description | EPSRC Supergen Solar Challenge |
| Amount | £1,293,323 (GBP) |
| Funding ID | EP/M024911/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 09/2015 |
| End | 11/2018 |
| Description | EPSRC Supergen Solar Hub: International and Industrial Engagement Fund |
| Amount | £8,320 (GBP) |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Department | SuperSolar Hub |
| Sector | Academic/University |
| Country | United Kingdom |
| Start | 04/2015 |
| Description | EPSRC Supergen Solar Hub: Supersolar International Conference Fund |
| Amount | £500 (GBP) |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Department | SuperSolar Hub |
| Sector | Academic/University |
| Country | United Kingdom |
| Start | |
| Description | EPSRC Supergen Solar Network+ |
| Amount | £1,020,414 (GBP) |
| Funding ID | EP/S000763/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 07/2018 |
| End | 06/2022 |
| Description | ISIS Facility Development and Utilisation Studentship |
| Amount | £33,501 (GBP) |
| Organisation | Science and Technologies Facilities Council (STFC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 10/2022 |
| End | 09/2026 |
| Description | Impact Acceleration Account |
| Amount | £26,368 (GBP) |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 12/2018 |
| End | 05/2019 |
| Description | Royal Society International Exchanges Scheme |
| Amount | £11,935 (GBP) |
| Funding ID | IE130110 |
| Organisation | The Royal Society |
| Sector | Charity/Non Profit |
| Country | United Kingdom |
| Start | 09/2013 |
| End | 08/2015 |
| Description | SuperSolar Hub: - Supergen Solar Hub: International and Industrial Engagement Fund |
| Amount | £7,100 (GBP) |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 02/2020 |
| End | 09/2020 |
| Description | Terabotics - terahertz robotics for surgery and medicine |
| Amount | £8,000,773 (GBP) |
| Funding ID | EP/V047914/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 08/2021 |
| End | 08/2026 |
| Description | ISFH |
| Organisation | Institute for Solar Energy Research |
| Country | Germany |
| Sector | Academic/University |
| PI Contribution | Scientific studies of the influence of defects on silicon materials for photovoltaics. |
| Collaborator Contribution | Access to surface passivation facilities, and intellectual input into scientific studies. |
| Impact | Many scientific papers, including some of those returned with this submission. |
| Start Year | 2009 |
| Description | SunEdison |
| Organisation | SunEdison Semiconductor |
| Country | United States |
| Sector | Private |
| PI Contribution | Experimental studies of defects in silicon materials for integrated circuits and photovoltaics. |
| Collaborator Contribution | Materials, characterisation and technical expertise. |
| Impact | Many academic papers, including those returned in this submission. |