Transformational concepts in window electrode design for emerging thin film photovoltaics

Photovoltaic (PV) devices convert sunlight directly into electricity and form an increasingly important part of the global renewable energy landscape. Today's PVs are based on conventional semiconductors which are energy-intensive to produce and restricted to rigid flat plate designs. The next generation of PVs will be based on very thin films of semiconductors that can be processed from solution at low temperature, which opens the door to exceptionally low cost manufacturing processes and new application areas not available to today's rigid flat plate PVs, particularly in the areas of transportation and buildings integration. The emerging generation of thin film PVs also offer exceptional carbon dioxide mitigation potential because they are expected to return the energy used in their fabrication within weeks of installation. However, this potential can only be achieved if the electrode that allows light into these devices is low cost and flexible, and at present no electrode technology meets both the cost constraint and technical specifications needed. This proposal seeks to address this complex and inherently interdisciplinary challenge using three new and distinct approaches based on the use of nano-structured films of metal less than 100 metal atoms in thickness. The first approach focuses on the development of a low cost, large area method for the fabrication of metal film electrodes with a dense array of holes through which light can pass unhindered. The second approach seeks to determine design rules for a new type of 'light-catching' electrode that interacts strongly with the incoming light, trapping and concentrating it at the interface with the semiconductor layer inside the device responsible for converting the light into electricity. The final approach is based on combining ultra-thin metal films with ultra-thin films of transparent semiconductor materials to achieve double layer electrodes with exceptional properties resulting from spontaneous intermixing of the two thin solid films. The UK is a global leader in the development of next generation PVs with a growing number of companies now focused on bringing them to market, and so the outputs of the proposed programme of research has strong potential to directly increase the economic competitiveness of the UK in this young sector and would help to address the now time critical challenge of climate change due to global warming.

The emergence of a low cost photovoltaic (PV) technology suitable for transport applications and buildings integration would have far-reaching societal and environmental benefits: (i) by providing a source of electricity for the 1.3 billion people currently without access to grid electricity, many of whom live in buildings not capable of supporting conventional PVs.; (ii) by helping to increase the security of electricity supply.; and (iii) by reducing reliance on fossil fuels, thereby helping to combat global warming and climate change. The emerging generation of thin film photovoltaics (e-TFPVs) offer a path to a dramatic reduction in the cost of manufacturing PVs, and their low thickness renders them light weight, low profile and flexible, which opens the door to applications in vehicles and building facades not available to conventional flat plate PVs. e-TFPVs also offer exceptional carbon dioxide mitigation potential because they are expected to return the energy used in their fabrication within weeks of installation.
The UK is a global leader in the development of e-TFPVs, with an intensive research effort in this area in a number of its leading universities, and a growing number of enterprises dedicated to bringing e-TFPVs to the market, including Dyesol UK, SolarPress, Oxford PV and Eight19. Maintaining this position, at a time when these technologies are on the verge of commercialisation, is important to the UK economy because it sets the scene for the UK to firmly establish an industry base in this sector. The aforementioned companies stand to benefit directly from the outputs of this proposal because: (i) it is widely recognised that the full commercial potential of e-TFPVs can only be realised if the electrode that allows light into these devices is low cost and flexible, and the primary output of this project would be a window electrode technology matched to the needs of e-TFPVs.; (ii) the specialist high level skills and experience of the researchers involved with this project would represent a potential source of skilled staff at the project end. UK based companies not directly engaged with e-TFPV commercialisation but who are well positioned to benefit from the project outputs include those that develop and/or manufacture non-PV based devices that require a transparent electrode, including displays, sensors and emerging semi-transparent electronic applications. These companies would benefit if the cost, form or functionality of their product is improved by switching to the transparent electrode technology developed in this project. UK based examples include Cambridge Display Technology (low energy solid state lighting), Molecular Vision (chemical sensing), PolyPhotonix (healthcare) and FlexEnable (flexible electronics). Companies that produce glass coated with optically thin metal films for building and transport applications, such as low emissivity glass, smart glass and anti-reflective coatings would also stand to benefit, since the new method of fabricating patterned metal films over large areas developed in this project may impart a cost advantage, or improved properties as compared to existing methods. Companies in this space include Pilkington glass, Corning, Saint Gobain and Tata. Companies that develop and manufacture machines and processes for depositing and patterning metal films on flexible substrates would also be beneficiaries if they choose to become involved with translating the outputs of the project from the laboratory to end users (e.g. e-TFPV manufacturers). These include Bobst Manchester and the Centre for Process Innovation (CPI) in Sedgefield. The strategy for ensuring that these potential beneficiaries are able to engage with the outputs of this project includes the establishment of an industrial advisory board and is detailed in the Pathways to Impact Plan.