New designs for thin film solar cells
Lead Research Organisation:
University of Liverpool
Department Name: Physics
Abstract
To limit global warming to 2degC by 2050, renewable power generation must increase from 15 to 65% (Int Renewable Energy Association [1]), and all scenarios concur that solar photovoltaic electricity generation will play a large part in this: The International Energy Agency (IEA) World Energy Outlook forecasts that solar electricity production should increase from 430 Tw-h in 2017 to 6,410 Tw-h in 2040 in its 'Sustainable Scenario' [2].
Solar PV (photovoltaics) is making a strong contribution, with a 24% year on year increase in sales from 2010 to 2017. This has been driven by the tumbling costs of the leading solar PV technology, wafer silicon, which has seen massive production expansion in the Far East. It accounts for 95% of the market. Costs continue to fall by about 25% for each doubling of cumulative installed capacity ('Moore's law for solar').
Low cost thin film competitors to silicon have the advantage that they use thin coatings of highly absorbing compound semiconductors rather than sliced wafers. They are big business in themselves, with a turnover of an estimated $1,000 million per annum for CdTe alone. Nevertheless, the thin film technologies must continually improve their cost/performance ratio in order to stay ahead of the ever-falling costs of wafer silicon production. For example, the largest thin film PV manufacturer worldwide, First Solar, has just doubled the size of its CdTe modules and changed its junction design in order to maintain its market position as having the lowest cost PV available.
Despite the commercial success of thin film PV, there are relatively few large commercial players. One of the reasons for this is the technological risk, and the amount of know-how required to produce the solar cells. In the case of the market leader, CdTe for example, the basic design of the semiconductor p-n junction has remained unchanged for 40 yrs. However, it contains some basic materials weaknesses that cannot be overcome. In particular, the CdTe absorber is p-type so as to make it compatible with the n-type transparent electrode. For fundamental materials reasons this limits the voltage achievable, and it makes true Ohmic contacting impossible. Both of these factors act to limit the energy conversion performance of the solar cells in practice.
In this programme we will design and fabricate a new type of thin film solar cell architecture that avoids these issues and has the potential for higher efficiency performance with simplified manufacturing protocols. We will use n-type CdTe absorbers, which do not suffer from either the doping limitations or contacting issues of p-type. The work programme will centre on re-designing the solar cell architecture in order to accommodate the n-type CdTe and to realize its advantages.
We expect that the new design will be capable of generating open circuit voltages of 1 V compared to the 0.87 V of present day structures. This will push solar energy conversion efficiencies up to about 25%. Moreover, since the device processing and contacting will not need to rely on 'black box' processes and know how, the new design will be more producible and will present an attractive alternative to manufacturers.
[1] Renewable Power Generation Costs in 2017
https://www.irena.org/publications/2018/Jan/Renewable-power-generation-costs-in-2017
[2] International Energy Agency (IEA) World Energy Outlook 'Sustainable Scenario'
https://www.iea.org/weo2018/
Solar PV (photovoltaics) is making a strong contribution, with a 24% year on year increase in sales from 2010 to 2017. This has been driven by the tumbling costs of the leading solar PV technology, wafer silicon, which has seen massive production expansion in the Far East. It accounts for 95% of the market. Costs continue to fall by about 25% for each doubling of cumulative installed capacity ('Moore's law for solar').
Low cost thin film competitors to silicon have the advantage that they use thin coatings of highly absorbing compound semiconductors rather than sliced wafers. They are big business in themselves, with a turnover of an estimated $1,000 million per annum for CdTe alone. Nevertheless, the thin film technologies must continually improve their cost/performance ratio in order to stay ahead of the ever-falling costs of wafer silicon production. For example, the largest thin film PV manufacturer worldwide, First Solar, has just doubled the size of its CdTe modules and changed its junction design in order to maintain its market position as having the lowest cost PV available.
Despite the commercial success of thin film PV, there are relatively few large commercial players. One of the reasons for this is the technological risk, and the amount of know-how required to produce the solar cells. In the case of the market leader, CdTe for example, the basic design of the semiconductor p-n junction has remained unchanged for 40 yrs. However, it contains some basic materials weaknesses that cannot be overcome. In particular, the CdTe absorber is p-type so as to make it compatible with the n-type transparent electrode. For fundamental materials reasons this limits the voltage achievable, and it makes true Ohmic contacting impossible. Both of these factors act to limit the energy conversion performance of the solar cells in practice.
In this programme we will design and fabricate a new type of thin film solar cell architecture that avoids these issues and has the potential for higher efficiency performance with simplified manufacturing protocols. We will use n-type CdTe absorbers, which do not suffer from either the doping limitations or contacting issues of p-type. The work programme will centre on re-designing the solar cell architecture in order to accommodate the n-type CdTe and to realize its advantages.
We expect that the new design will be capable of generating open circuit voltages of 1 V compared to the 0.87 V of present day structures. This will push solar energy conversion efficiencies up to about 25%. Moreover, since the device processing and contacting will not need to rely on 'black box' processes and know how, the new design will be more producible and will present an attractive alternative to manufacturers.
[1] Renewable Power Generation Costs in 2017
https://www.irena.org/publications/2018/Jan/Renewable-power-generation-costs-in-2017
[2] International Energy Agency (IEA) World Energy Outlook 'Sustainable Scenario'
https://www.iea.org/weo2018/
Planned Impact
1. Society in general as a beneficiary:
Society in general stands to benefit from all activity that reduces CO2 emissions: the Intergovernmental Panel on Climate Change's "Special Report on Global Warming of 1.5 degrees" (2018) highlights the importance of limiting further anthropomorphic climate change [1]. Its mitigation pathways analysis highlights the growing contribution that solar photovoltaics can make going forward to 2050 and 2100.
2. UK perspective on climate change impacts and actions:
The UK Government's "Stern Review on the Economics of Climate Change" makes it clear that the cost of early action and investment to stem climate change is very much lower than the cost penalty of delaying [2]. This proposal speaks to new opportunities for solar electricity generation that will contribute to reducing CO2 emissions at an early stage.
3. Western manufacturing economies as a beneficiary:
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. Presently the manufacture of solar photovoltaic modules is dominated by the Far East, where mass production has realised the economies of scale and the resulting cost reduction. Production has largely shipped out of Europe. This proposal aims to stimulate a new design of low cost solar cell that can undercut the costs of wafer silicon technology. The aim is to use a technological innovation to increase the competitiveness of advanced new technologies to gain a manufacturing advantage over Far East dominance. An alternative view is that thin film PV has to continually re-invent itself to stay in the game - this proposal addresses that need.
4. Particular industries as beneficiaries:
a) NSG - Pilkington is the largest supplier of coated glass to the world solar PV industry. Its European Technical Centre is based at Lathom, Lancs, UK, and it also has manufacturing plants in the North West. The proposed design of solar cell will use coated glass and therefore have a direct benefit to the glass industry, not least NSG - Pilkington
b) Solar cell manufacturers - it is likely that the existing major manufacturers of thin film PV will have a direct interest in new technology licences. For example, Calyxo and CT Solar in Germany, and First Solar in the USA: They have the manufacturing experience to be able to take advantage of a new opportunity.
c) PV installation industries - a new wave of low cost PV products will act to stimulate the installation market and associated industries.
Academics as beneficiaries.
See "Academic Beneficiaries" statement
[1] https://www.ipcc.ch/sr15/chapter/2-0/ - accessed 20 Feb 2019
[2] https://en.wikipedia.org/wiki/Stern_Review - accessed 20 Feb 2019
Society in general stands to benefit from all activity that reduces CO2 emissions: the Intergovernmental Panel on Climate Change's "Special Report on Global Warming of 1.5 degrees" (2018) highlights the importance of limiting further anthropomorphic climate change [1]. Its mitigation pathways analysis highlights the growing contribution that solar photovoltaics can make going forward to 2050 and 2100.
2. UK perspective on climate change impacts and actions:
The UK Government's "Stern Review on the Economics of Climate Change" makes it clear that the cost of early action and investment to stem climate change is very much lower than the cost penalty of delaying [2]. This proposal speaks to new opportunities for solar electricity generation that will contribute to reducing CO2 emissions at an early stage.
3. Western manufacturing economies as a beneficiary:
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. Presently the manufacture of solar photovoltaic modules is dominated by the Far East, where mass production has realised the economies of scale and the resulting cost reduction. Production has largely shipped out of Europe. This proposal aims to stimulate a new design of low cost solar cell that can undercut the costs of wafer silicon technology. The aim is to use a technological innovation to increase the competitiveness of advanced new technologies to gain a manufacturing advantage over Far East dominance. An alternative view is that thin film PV has to continually re-invent itself to stay in the game - this proposal addresses that need.
4. Particular industries as beneficiaries:
a) NSG - Pilkington is the largest supplier of coated glass to the world solar PV industry. Its European Technical Centre is based at Lathom, Lancs, UK, and it also has manufacturing plants in the North West. The proposed design of solar cell will use coated glass and therefore have a direct benefit to the glass industry, not least NSG - Pilkington
b) Solar cell manufacturers - it is likely that the existing major manufacturers of thin film PV will have a direct interest in new technology licences. For example, Calyxo and CT Solar in Germany, and First Solar in the USA: They have the manufacturing experience to be able to take advantage of a new opportunity.
c) PV installation industries - a new wave of low cost PV products will act to stimulate the installation market and associated industries.
Academics as beneficiaries.
See "Academic Beneficiaries" statement
[1] https://www.ipcc.ch/sr15/chapter/2-0/ - accessed 20 Feb 2019
[2] https://en.wikipedia.org/wiki/Stern_Review - accessed 20 Feb 2019
Organisations
People |
ORCID iD |
| Ken Durose (Principal Investigator) | |
| Jonathan Major (Co-Investigator) |
Publications
Don C
(2023)
Multi-Phase Sputtered TiO 2 -Induced Current-Voltage Distortion in Sb 2 Se 3 Solar Cells
in Advanced Materials Interfaces
Herklotz F
(2022)
Oxygen in antimony triselenide: An IR absorption study
in Applied Physics Letters
Hobson T
(2022)
N-type CdTe Thin Films via In-Situ Indium Doping
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
Shiel H
(2021)
Band alignment of Sb2O3 and Sb2Se3
in Journal of Applied Physics
Smiles MJ
(2022)
GeSe photovoltaics: doping, interfacial layer and devices.
in Faraday discussions
Thomas L
(2022)
An investigation into the optimal device design for selenium solar cells
in Energy Reports
Thomas L
(2022)
Insights into post-growth doping and proposals for CdTe:In photovoltaic devices
in Journal of Physics: Energy
| Description | The aim of the project was to redesign the already successful solar cell based on cadmium telluride in order to take advantage of some basic materials properties with the aim of paving the way to further improvements in its potential for solar electricity generation. In particular we started from the hypothesis that the present day limits to the voltage achievable (which are lower than expected) can be overcome by moving from the ubiquitous p-type conductivity to n-type. The detail is that the doping limit achievable for n-type is higher than for p-type and that should enable an increase in voltage. We demonstrated that n-type doping of thin film CdTe materials is indeed possible by two different routes, these being post-growth diffusion and in-situ growth of doped films using a pre-doped source material. The dopant was indium. While traditional transport based measurement of the carrier type failed due to the grain boundaries, it was nevertheless possible to determine that n-type conduction operated by the use of hard x-ray photoemission spectroscopy. This determined the Fermi level position which indicated that the materials were indeed n-type. A new fact about doping was also discovered and it was related to the universal use of chloride processing in order to achieve high efficiency conventional p-type cells: use of chlorides was found to compensate the n-type doping making the material intrinsic. Usually the chlorine is considered essential to cause electrical passivation of the grain boundaries. However, here we demonstrated it to be a powerful compensation agent. Photovoltaic devices formed using indium doping have, at present, low performances. Since conductivity in CdTe is known to arise from a combination of both extrinsic (impurity) and intrinsic (vacancy) doping, it is likely that the performances achieved so far have been limited by the stoichiometry of the material. |
| Exploitation Route | The findings represent a foundation of knowledge that will be useful in the development of n-type CdTe solar cells and also to seed the idea to make other kinds of solar cells using n-type absorbers. |
| Sectors | Energy |