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.

The history of II-VI metal-organic chemical vapour deposition (MOCVD) goes back as far as IIII-V MOCVD but has not had the traction in applications for lasers, LEDs and high frequency devices that has been experienced by III-V semiconductors. A new generation of MOCVD equipment can more fully exploit the potential of II-VI semiconductors and explore new oxides and chalcogenides in the exiting areas of III-VIs such as Ga2O3 and 2-D semiconductors such as MoS2. There is now a compelling case for the UK to have state-of-the-art MOCVD equipment for compound semiconductors (CS) covering oxide and chalcogenide materials that are not covered by existing centres such as the National Epitaxy Facility at Sheffield, Cambridge and UCL, and Institute of CS at Cardiff. The UK has a golden opportunity to build on our strengths in CS research that will drive innovation across a range of new opto-electronic and power electronic devices. The need arises from a new generation of functional compound semiconductor materials to capture the unique properties of oxide and chalcogenide compound semiconductors (CSs), complementing III-V compounds and silicon, and opening new application areas in optoelectronics, energy and healthcare. It is proposed that we buy the Aixtron Close Couple Showerhead (CCS) reactor that has been proven to be the reactor design of choice for GaN deposition and will be the ideal equipment to deposit high quality oxide and chalcogenide compound semiconductor materials. "The UK needs this facility, which it does not have at present. Swansea is an excellent place for it." - Prof. Sir Colin Humphreys (Cambridge). "This proposed research facility will perfectly complement the installation of ~100 production MOCVD reactors leveraged by a £375M investment by IQE Plc over 2018-2022" - Dr Wyn Meredith (CSC, Cardiff). The CCS reactor will be installed in a new building for the Centre for Integrated Semiconductor Materials (CISM) (due for completion in Q1 2021) on the Swansea University Bay Campus. Over 140 m2 of specialist materials laboratory space will be allocated to the MOCVD reactor and complementary materials and characterisation equipment from Professor Irvine's laboratory. This new laboratory will be managed by Professor Irvine's team to provide high quality oxide and chalcogenide CSs to our research partners in Swansea University, other UK universities, industrial partners and to international collaborators. This will put the UK at the forefront of new science and technology using oxide and chalcogenide CSs for applications including high efficiency photovoltaic solar cells, Light harvesting quantum wire opto-electronic devices, piezoelectric energy harvesting, high breakdown voltage power electronic devices and light emitters. This new science and technology will benefit EPSRC priorities of "21st Century Products" and "Sustainable Industries" through enabling smart new products that could be rapidly prototyped through well proven manufacturing capability for MOCVD in the UK and enabling the application of more sustainable materials and reduced materials usage. This exciting opportunity is detailed in the case for support.

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.

PV-21 is the UK's inorganic solar photovoltaic (PV) research programme / this proposal is for a renewal for the second four year cycle. The Consortium has sharpened its focus on the science that will deliver our medium to long term goal of 'making a major contribution to achieving competitive PV solar energy'. In its initial period of activity, the Consortium has put in place lab-scale facilities for making three main types of solar cells based on thin film absorbers - copper indium diselenide, cadmium telluride and ultra thin silicon - using a range of methods. In the renewal programme, these three 'Technology Platforms' form the basis for testing new processes and concepts. To reduce costs, we shall concentrate on critical materials and PV device issues. For large-scale PV manufacture, the materials costs dominate, and together with module efficiency determine the cost per kW peak. A closely related issue is sustainability. For example the metal indium is a key component in PV, but is rare and expensive ($660/kg in 2007). Reducing the thickness of semiconductor by one millionth of a metre (1 micron) in 10% efficient cells with a peak generating capacity of 1GW would save 50 tonnes of material. The renewal programme therefore includes work on both thickness reduction and on finding alternative sustainable low cost materials (absorbers and transparent conductors). To increase efficiency we shall work on aspects of grain boundaries and nanostructures thin films as well as on doping. Nanostructures will also be exploited to harvest more light, and surface sensitization of thin film silicon cells by energy transfer from fluorescent dyes will also be investigated as a means of making better use of sunlight and substantially reducing the required film thickness to as low 0.2 microns. In order to ensure a focus on cost effectiveness, the renewal programme includes a technical economics package that will examine cost and sustainability issues. Future links between innovative concepts and industry are ensured by a 'producibility' work package. Two highly relevant 'plus' packages have been submitted alongside the renewal proposal, these being on a) thin film silicon devices, grain engineering and new concepts, and b) new absorber materials. The Consortium will also continue to run the successful UK network for PV materials and device research, PV-NET, which is a forum for the UK academic and industrial research communities. The Supergen funding mechanism has enabled the Consortium to assemble and fully integrate a critical mass of PV researchers in the UK, and the work packages outlined in the proposal interweave the skills and capabilities of seven universities and nine industrial partners. PV-21 is also plays an important role in skills development, with nine PhD students due to be trained in the first cohort. The EPSRC Supergen funding mechanism is absolutely vital for the continued growth and strength of the UK PV materials research effort.

PV-21 is the UK's inorganic solar photovoltaic (PV) research programme / this proposal is for a renewal for the second four year cycle. The Consortium has sharpened its focus on the science that will deliver our medium to long term goal of 'making a major contribution to achieving competitive PV solar energy'. In its initial period of activity, the Consortium has put in place lab-scale facilities for making three main types of solar cells based on thin film absorbers - copper indium diselenide, cadmium telluride and ultra thin silicon - using a range of methods. In the renewal programme, these three 'Technology Platforms' form the basis for testing new processes and concepts. To reduce costs, we shall concentrate on critical materials and PV device issues. For large-scale PV manufacture, the materials costs dominate, and together with module efficiency determine the cost per kW peak. A closely related issue is sustainability. For example the metal indium is a key component in PV, but is rare and expensive ($660/kg in 2007). Reducing the thickness of semiconductor by one millionth of a metre (1 micron) in 10% efficient cells with a peak generating capacity of 1GW would save 50 tonnes of material. The renewal programme therefore includes work on both thickness reduction and on finding alternative sustainable low cost materials (absorbers and transparent conductors). To increase efficiency we shall work on aspects of grain boundaries and nanostructures thin films as well as on doping. Nanostructures will also be exploited to harvest more light, and surface sensitization of thin film silicon cells by energy transfer from fluorescent dyes will also be investigated as a means of making better use of sunlight and substantially reducing the required film thickness to as low 0.2 microns. In order to ensure a focus on cost effectiveness, the renewal programme includes a technical economics package that will examine cost and sustainability issues. Future links between innovative concepts and industry are ensured by a 'producibility' work package. Two highly relevant 'plus' packages have been submitted alongside the renewal proposal, these being on a) thin film silicon devices, grain engineering and new concepts, and b) new absorber materials. The Consortium will also continue to run the successful UK network for PV materials and device research, PV-NET, which is a forum for the UK academic and industrial research communities. The Supergen funding mechanism has enabled the Consortium to assemble and fully integrate a critical mass of PV researchers in the UK, and the work packages outlined in the proposal interweave the skills and capabilities of seven universities and nine industrial partners. PV-21 is also plays an important role in skills development, with nine PhD students due to be trained in the first cohort. The EPSRC Supergen funding mechanism is absolutely vital for the continued growth and strength of the UK PV materials research effort.