Doped Emitters to Unlock Lowest Cost Solar Electricity
Lead Research Organisation:
SWANSEA UNIVERSITY
Department Name: College of Engineering
Abstract
Solar PV is on the cusp of becoming the lowest cost source of electricity for many regions of the world, displacing fossil fuels, with the prospect of dramatically reducing carbon emissions. The second generation thin film PV based on CdTe has lower manufacturing cost and lower carbon footprint than silicon PV. This proposal will enable the solar energy conversion efficiency of thin film CdTe PV modules to equal or exceed that of silicon and enabling more rapid and wider adoption of solar PV electricity.
This proposal brings fresh thinking to the front emitter layer that is widely recognised in the CdTe PV community as being the limiting factor in realising the potential of the arsenic doped CdTe and CdSeTe absorber layers. This is predicted to achieve over 25% cell efficiency and over 22% module efficiency. To achieve this goal we have put together a world leading team to work on a new n-type emitter layer. The teams at Swansea-CSER and Loughborough-CREST have combined expertise on As doping of the CdTe absorber layer along with sputter deposition of oxide layers. The world leading team includes project partners - Colorado State University (leading academic team in the USA), First Solar (leading thin film PV manufacturer) and NSG Pilkington (leading coated glass products for thin film PV).
The challenge for realising the potential for arsenic doped CdTe (pioneered by the Swansea team) is to combine the acceptor doped CdTe layer with a transparent emitter layer where the n-type doping concentration exceeds the acceptor doping concentration of the CdTe layer. For an acceptor doping of >1x1016 cm-3, the emitter donor doping needs to be >1x1017 cm-3. In addition the conduction band alignment must give a small positive step for electron collection which will reduce non-radiative recombination. To achieve this exacting specification we will explore a wide range of potential oxides and their alloys with different dopants using combinatorial techniques. This will be matched to the optimised alloy composition and doping of the CdSeTe absorber layer using MOCVD. Stability of candidate doped emitters will be tested from an early stage with regard to air exposure and exposure to process steps in fabricating the complete thin film PV device. Extensive materials and device characterisation will be used to understand the relationship between the novel doped emitters and improved PV cell efficiency.
This proposal brings fresh thinking to the front emitter layer that is widely recognised in the CdTe PV community as being the limiting factor in realising the potential of the arsenic doped CdTe and CdSeTe absorber layers. This is predicted to achieve over 25% cell efficiency and over 22% module efficiency. To achieve this goal we have put together a world leading team to work on a new n-type emitter layer. The teams at Swansea-CSER and Loughborough-CREST have combined expertise on As doping of the CdTe absorber layer along with sputter deposition of oxide layers. The world leading team includes project partners - Colorado State University (leading academic team in the USA), First Solar (leading thin film PV manufacturer) and NSG Pilkington (leading coated glass products for thin film PV).
The challenge for realising the potential for arsenic doped CdTe (pioneered by the Swansea team) is to combine the acceptor doped CdTe layer with a transparent emitter layer where the n-type doping concentration exceeds the acceptor doping concentration of the CdTe layer. For an acceptor doping of >1x1016 cm-3, the emitter donor doping needs to be >1x1017 cm-3. In addition the conduction band alignment must give a small positive step for electron collection which will reduce non-radiative recombination. To achieve this exacting specification we will explore a wide range of potential oxides and their alloys with different dopants using combinatorial techniques. This will be matched to the optimised alloy composition and doping of the CdSeTe absorber layer using MOCVD. Stability of candidate doped emitters will be tested from an early stage with regard to air exposure and exposure to process steps in fabricating the complete thin film PV device. Extensive materials and device characterisation will be used to understand the relationship between the novel doped emitters and improved PV cell efficiency.
Publications
Blakesley J
(2024)
Roadmap on established and emerging photovoltaics for sustainable energy conversion
in Journal of Physics: Energy
Blakesley J
(2023)
Roadmap on Photovoltaic Absorber Materials for Sustainable Energy Conversion
Clayton A
(2022)
MOCVD of II-VI HRT/Emitters for Voc Improvements to CdTe Solar Cells
in Coatings
Clayton A
(2021)
MOCVD of II-VI HRT/emitters for Voc improvements to CdTe solar cells
Clayton A
(2021)
MOCVD of II-VI HRT/emitters for Voc improvements to CdTe solar cells
Davis R
(2024)
Comparative study of cadmium telluride solar cell performance on different TCO-coated substrates under concentrated light intensities
in Progress in Photovoltaics: Research and Applications
Hall R
(2021)
Back contacts materials used in thin film CdTe solar cells-A review
in Energy Science & Engineering
Irvine S
(2023)
Creating metal saturated growth in MOCVD for CdTe solar cells
in Journal of Crystal Growth
Kartopu G
(2023)
A facile photolithography process enabling pinhole-free thin film photovoltaic modules on soda-lime glass
in Solar Energy Materials and Solar Cells
| Description | Optimizing Material Composition and Growth Conditions: the project has explored the effects of growing CdTe absorber layers under cadmium-rich (Cd-rich) conditions using metal-organic chemical vapor deposition (MOCVD). This approach resulted in smoother surfaces and larger crystal grains, which are beneficial for enhancing the efficiency of solar cells. Another aspect to the project examined the impact of different cadmium sources on the properties of CdTe thin films, highlighting the importance of controlling composition and stoichiometry during deposition to achieve desired electrical and optical characteristics. Additionally, research into the use of high-resistance transparent (HRT) layers, such as ZnO, demonstrated that these layers can withstand higher annealing temperatures during the chlorine heat treatment process, leading to improved open-circuit voltage and overall device performance. The project has also focused on the structural aspects of CdTe films, revealing that higher substrate temperatures during deposition lead to larger grain sizes and improved crystallinity. This structural enhancement correlates with better electrical properties, such as increased carrier concentration and reduced resistivity. Furthermore, the incorporation of arsenic as a dopant in the CdTe layer has been shown to improve junction quality, resulting in higher current density and overall efficiency. These findings underscore the critical role of precise control over material composition, deposition conditions, and post-deposition treatments in optimizing the performance of CdTe-based solar cells. Collectively, these advancements contribute to the development of more efficient and cost-effective CdTe solar cells, paving the way for broader adoption of this technology in renewable energy applications. |
| Exploitation Route | The introduction of high-resistance transparent (HRT) layers, such as ZnO, has been shown to improve the open-circuit voltage and overall efficiency of CdTe solar cells. Manufacturers can incorporate these HRT layers into their module designs to produce more efficient solar panels. This enhancement is particularly valuable for large-scale installations where maximizing energy output is crucial.. The findings from these studies provide a foundation for ongoing collaboration between researchers and industry stakeholders. By sharing data and insights, both parties can work together to refine CdTe solar cell technologies, address any emerging challenges, and accelerate the commercialization of next-generation solar energy solutions. |
| Sectors | Electronics Energy Environment |
| Description | Low-cost CdTe-based PV power for communications and energy applications in space |
| Amount | £1,522,894 (GBP) |
| Funding ID | UKRI1489 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 05/2025 |
| End | 05/2028 |
| Title | Supplementary information files for "CdTe absorber layers grown under Cd-rich conditions by MOCVD: Impact on surface morphology and structure" |
| Description | Supplementary files for article "CdTe absorber layers grown under Cd-rich conditions by MOCVD: Impact on surface morphology and structure" The analyses of surface morphology and microstructural properties of CdTe thin film absorber layers, deposited by metal organic chemical vapour deposition (MOCVD) on CdS/CdZnS/FTO-coated glass substrates as a function of different growth conditions (non-saturated or Cd-saturated growth condition and post-growth CdCl2 heat treatment) are presented. Scanning electron microscopy (SEM) images showed that the CdTe absorber surface morphology was relatively smoother with Cd-saturated growth compared to non-saturated conditions, while using a similar II/VI precursor partial pressure ratio. Microstructural characterisation using electron back scatter diffraction (EBSD) measurements indicate a strong influence of the II/VI ratios on the crystalline structure and degree of recrystallisation in Cd-saturated deposited CdTe absorber layers. CdTe absorber layers from a low II/VI ratio of 2 showed a strong Te(A1) Raman spectra band, characteristic of a Te rich composition, whilst a Cd-saturated composition was confirmed in the case of II/VI ratio of 4, as Te(A1) band was significantly suppressed. Cd-saturated grown CdTe:As (II/VI = 4), combined with a CdCl2 activation process at 440 °C, yielded optimum, highly randomized textured absorber with large grains. Reduced [111] oriented grains and suppression of Te(A1) mode was found to lead to higher VOC in devices. A high efficiency CdTe:As solar cell with a high VOC of 825 mV was measured based on the optimum growth condition for the absorber layers. © The Author(s), CC BY 4.0 |
| Type Of Material | Database/Collection of data |
| Year Produced | 2025 |
| Provided To Others? | Yes |
| URL | https://repository.lboro.ac.uk/articles/dataset/Supplementary_information_files_for_CdTe_absorber_la... |
| Title | Supplementary information files for "Development of ZnO buffer layers for as-doped CdSeTe/CdTe solar cells with efficiency exceeding 20%" |
| Description | Supplementary files for article "The front buffer layer plays an important role in CdSeTe/CdTe solar cells and helps achieve high conversion efficiencies. Incorporating ZnO buffer layers in the CdSeTe/CdTe device structure has led to highly efficient and stable solar cells. In this study, the optimization of ZnO buffer layers for CdSeTe/CdTe solar cells is reported. The ZnO films are radio frequency sputter-deposited on SnO2:F coated soda-lime glass substrates. The substrate temperature for the ZnO deposition is varied from 22 to 500 °C. An efficiency of 20.74% is achieved using ZnO deposited at 100 °C. The ZnO thickness is varied between 40 nm and 75 nm. Following the ZnO depositions, devices were fabricated using First Solar's CdSeTe/CdTe absorber, CdCl2 treatment, and back contact. The optimal ZnO deposition temperature and thickness is 100 °C and 65 nm, respectively. The STEM-EDX analysis shows that within the detection limits, chlorine is not detected at the front interface of the devices using ZnO deposited at 22 °C and 100 °C. However, depositing ZnO at 500 °C results in chlorine segregation appearing at the ZnO/CdSeTe boundary. This suggests that chlorine is not needed to passivate the ZnO/CdSeTe interface during the lower temperature depositions. The nanocrystalline ZnO deposited at lower temperatures results in a high-quality interface." ©The Author(s), CC BY 4.0 |
| Type Of Material | Database/Collection of data |
| Year Produced | 2025 |
| Provided To Others? | Yes |
| URL | https://repository.lboro.ac.uk/articles/dataset/Supplementary_information_files_for_Development_of_Z... |
| Description | First Solar |
| Organisation | First Solar, Inc |
| Country | United States |
| Sector | Private |
| PI Contribution | Providing data on novel doped emitters in CdSeTe solar cells and materials characterisation. |
| Collaborator Contribution | Using First Solar solar cell fabrication on novel doped emitters to evaluate performance. |
| Impact | Creating metal saturated growth in MOCVD for CdTe solar cells, S.J.C. Irvine a, O. Oklobia a, S. Jones a, D.A. Lamb a, G. Kartopu b, D. Lu c, G. Xiong c, Centre for Solar Energy Research, Faculty of Science & Engineering, Swansea University, OpTIC Centre, St. Asaph Business Park, LL17 0JD, UK b Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle upon Tyne NE1 8ST, UK c First Solar, Inc., 1035 Walsh Ave., Santa Clara, CA 95050, USA Journal of Crystal Growth Volume 607, 1 April 2023, 127124 |
| Start Year | 2022 |
| Description | Loughborough University, CREST |
| Organisation | Loughborough University |
| Department | Centre for Renewable Energy Systems Technology (CREST) |
| Country | United Kingdom |
| Sector | Academic/University |
| PI Contribution | Joint proposal where Loughborough CREST will produce new doped emitters that will be tested using doped absorber layers produced by Swansea University, CSER. |
| Collaborator Contribution | Materials characterisation and physical vapour deposition of doped oxides. |
| Impact | Project at early stage of collaboration. |
| Start Year | 2021 |
| Description | Loughborough University, CREST |
| Organisation | Loughborough University |
| Department | Centre for Renewable Energy Systems Technology (CREST) |
| Country | United Kingdom |
| Sector | Academic/University |
| PI Contribution | Joint proposal where Loughborough CREST will produce new doped emitters that will be tested using doped absorber layers produced by Swansea University, CSER. |
| Collaborator Contribution | Materials characterisation and physical vapour deposition of doped oxides. |
| Impact | Project at early stage of collaboration. |
| Start Year | 2021 |
| Description | Semiconductor cleanroom workshop |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Study participants or study members |
| Results and Impact | Dr Ochai Oklobia attended the Royce Cleanroom Training Course at University of Leeds. This was a 1 week course in which Dr Oklobia received practical and classroom training for cleanroom techniques. |
| Year(s) Of Engagement Activity | 2024 |
| Description | Two day workshop on photovoltaics |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | Local |
| Primary Audience | Postgraduate students |
| Results and Impact | Two day workshop discussing Swansea and Imperial College photovoltaic activities. Delivered a 20 minute presentation on chalcogenide MOCVD PV |
| Year(s) Of Engagement Activity | 2023 |