Development of a high performance laminated transparent top-electrode for emerging thin-film photovoltaics

Photovoltaic (PV) devices convert sunlight directly into electricity and so are set to play a major role in the global renewable energy landscape in the coming decades as humanity transitions to a low carbon future. Today's PVs are based on conventional semiconductors which are relatively energy-intensive to produce and largely restricted to rigid flat plate designs. Consequently, PVs that can be fabricated by printing at low temperature onto flexible substrates are attractive for a broad range of applications in buildings and transportation, where flexibility, colour-tuneability, light-weight and low cost are essential requirements. Two emerging PV technologies that have strong potential to meet these requirements are organic PVs and perovskite PVs. It is however widely recognised that these classes of PV can only fulfill their full cost-advantage and functional advantages over conventional thin film PVs if a suitable transparent, flexible electrode is forthcoming. Indium-tin oxide (ITO) is currently the dominant transparent conductor used in opto-electronics, including PVs. However, its fragile ceramic nature makes it poorly compatible with flexible substrates and indium has been identified as a 'critical raw material' for the European economic area, due to the high risk of supply shortages expected in the next 10 years. Consequently there is a need to develop a viable alternative to ITO and conducting oxide electrodes in general, particularly for utility in PVs where large quantities will be needed in the coming decades to help address the threat posed by global warming. This proposal seeks to address this challenge by developing a high performance transparent electrode based on a copper grid that can be integrated with the rest of the PV device by simple lamination. This approach avoids the inevitable compromises in electrode transparency and conductivity that arise when using the conventional approach of fabricating the transparent electrode directly on top of the rest of device. Two unconventional approaches to fabricating this electrode using low cost sustainable materials and processes will be explored. The outputs have the potential to be transformative for the advancement of OPV and PPV, as well numerous other optoelectronic devices requiring a transparent top-electrode. The UK is a global leader in the development of materials and processes for next generation PVs and so the outputs of the proposed research has strong potential to directly increase the economic competitiveness of the UK in this increasingly important sector and will help to address the now time critical challenge of climate change due to global warming.

Currently, commercial enterprises focused on bringing perovskite and organic photovoltaics (PV) to market in the UK and Europe are Oxford PV (perovskite PV - UK), Epishine (organic PV - Sweden), InfinityPV (organic PV - Denmark) and Heliatek (organic PV - Germany). However, given the scale of the opportunity in this sector and rapid pace of scientific developments it is likely that over the timescale of the proposed project new players will enter the field. All of these high-tech companies stand to benefit from the primary project output: namely, a transparent electrode matched to the needs of top-illuminated, semi-transparent and bi-facial organic and perovskite PV designs, which will enable them to maximise the cost-advantage and functional advantages of their products over conventional PVs and of potential new application areas. Given the similarity in the design and fabrication processes used for PVs based on colloidal quantum dots and solid-state-dye sensitized PVs, it is reasonable to expect that the new transparent electrode developed during this project will be of interest to companies commercialising other types of thin film PV.

The following technology companies could also benefit from the specialist high level skills and experience of the PDRA on this project, by recruiting him/her at the end of the project.

1. Ossila Ltd (Sheffield) provides components, equipment, and materials to enable scientific research and discovery, particularly in the areas of organic and perovskite optoelectronics. A flexible transparent electrode suitable for direct lamination onto organic and perovskite PVs would be particularly enabling for new entrants to the field organic and perovskite PV research because it would remove the need for a high vacuum system for deposition of the top contact to complete the devices.

2. Companies that develop and/or manufacture non-PV based electronic devices that require a transparent electrode, including solid-state lighting, 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 flexible, laminated transparent electrode developed in this project. Examples of potential UK based beneficiaries include Cambridge Display Technology (low energy solid-state lighting), PolyPhotonix (healthcare) and FlexEnable (flexible electronics).

3. Companies that develop and manufacture machines and processes for depositing metal films on flexible substrates stand to benefit if they become involved with translating the outputs of the project from the laboratory to end users. These include Bobst Manchester and the Centre for Process Innovation (CPI) in Sedgefield. The latter, who are project partners on this proposal, help companies to prove and scale-up processes and to manufacture new products, and so are particularly well-placed to help maximise the pool of potential commercial beneficiaries.