Improved Understanding, Development and Optimisation of Perovskite-based Solar Cells

Solar is an increasingly important source of power generation. Word-wide installations of new solar modules will exceed 40GW in 2014 with over 1GW that capacity will be installed in the UK. The cost of modules has decreased sharply over the past two years due to over-supply from manufacturers. The cost reduction is now stimulating demand because the cost of energy from solar is now at 'grid parity' in some important regions of the world.

An exciting new type of solar cell based on thin film perovskite light absorbers has been discovered in the UK which has the potential to lower costs still further. The discovery has been made by a team of researchers at Oxford University. The progress they have made with these new devices has been unprecedented and in only two years the Oxford team has achieved conversion efficiencies exceeding 17%. Moreover, the technology has been protected by filing patent applications on the fundamental discoveries.

The Supergen Supersolar Hub comprises eight of the UK's leading University groups (including Oxford) engaged in the development of photovoltaic technologies. The Supergen SuperSolar Hub was quick to recognise the importance of the perovskite development and has already funded complementary research programmes in Hub member and Associate member laboratories through its flexible funding. This proposal for Supergen + funding will increase the scope and ambition of the Hub's perovskite research in modelling, synthesis, process optimization and characterization to boost conversion efficiencies still further and help maintain the UK's leadership position. In addition to the proposed research, proposals are made to increase the Hub's involvement with industry and with leading International laboratories to accelerate progress and lay the foundations for timely exploitation.

The Supergen SuperSolar Hub addresses the global challenge to produce energy in a clean and efficient manner. This proposal is at the cutting edge and will help to maintain the UK's lead in perovskite Photovoltaics (PV). The SuperSolar Hub has created a PV community in the UK that is inclusive and outward looking. The Hub will continue to catalyse academic-business co-operation to maximize the exploitation of publicly funded research and grow PV related industry and employment

Industrial Impact: The largest Photovoltaic market is utility scale power generation. This market is the "end goal" for the perovskite technology, and the costs play in its favour if the cell efficiency can be translated to module efficiency and if the stability can be improved. Building Integrated Photovoltaics (BIPV) is fast growing sector since there is a drive towards low impact buildings. A large fraction of the cost of solar power is the balance of systems (BOS). BIPV lends itself to tackling the BOS cost, since "solar cladding" can be integrated into the building infrastructure. Commercial buildings are being clad entirely in glass, implying that the additional cost of cladding a building with a solar glazing product removes the cost of the glass substrates. There is a trend towards using "curtain walling" where factory prefabricated cladding units are hung on the steel framework. Prefabricating solar cladding units, with all the wiring and interconnects designed to "click and connect" reduces the installation costs. To deliver BIPV, the photovoltaics should appear similar to existing glass facades. The market is currently supplied by amorphous silicon, which is made semi-transparent by being thin, but results in an unattractive red/orange or brown tint. Most glazed facades are colour neutral. By taking advantage of the spontaneous de-wetting of perovskite films upon crystallization, neutral density attenuation of light can be achieved with controllable levels of transmission. There is also a market for lightweight flexible solar cells, for applications such as power on lightweight commercial roofing, portable electronic power, automotive power and military applications. The perovskite crystal is inherently flexible with a high compressibility and bulk modulus, and efficient perovskite solar cells can be fabricated on flexible substrates. Oxford Photovoltaics Ltd will be a beneficiary of the research many other UK companies are part of a potential supply chain including NSG-Pilkington (TCO coated glass), M-solv Ltd (module interconnect technology),Tata Steel (PV coated cladding),Solar Century (BIPV supplier),Arup Partners (BIPV design),Polysolar (PV curtain walling) and Romag (semi-transparent windows).

Academic impact: The impact made on the academic community by recent developments at Oxford is extremely rare. The external recognition of the breakthrough is exemplified by both the Science and Nature Journals selecting perovskite PV as the breakthrough of the year in 2013. The work is interdisciplinary which broadens the impact to the whole of the science community.

Intellectual property: This project will generate intellectual property for perovskite PV technology with exciting commercial potential.

Training: The work will have impact through the experience in perovskite PV obtained by the postdoctoral researchers undertaking the work. Training in the development of perovskite PV is a major theme in our recently awarded EPSRC CDT in New and Sustainable Photovoltatics and projects will be open to the students in the CDT programme.

Government: The Hub is represented on the DECC UK PV Strategy Group and the PI is co-Chair of its Innovation Task Force. This enables the Hub to influence Government policy and DECC is aware of the opportunities for perovskite PV in BIPV applications.