Probing the energetics and loss mechanisms in molecular solar cells using luminescnce

This proposal seeks to establish a unified framework for understanding the - theoretical and practical - limits to efficiency of molecular or nanostructured heterojunction solar cells. The approach is to quantify and optimize the amount of electrical work available per absorbed photon using luminescence based techniques, electrical measurements and modelling. As examples of technologically relevant material systems we will study polymer:fullerene, polymer:nanoparticle and dye sensitized oxide structures, with the aim of describing these different heterojunctions within a single framework. Our approach is to control the energy of the charge separated state at the heterojunction through variations in materials and processes used, detect and measure the energy of that state and compare with the absorbed photon energy and the free enrgy delivered to an external circuit. Particular questions to be addressed concern the effect of the dielectric permittivity of the heterojunction medium (by comparing all organic with hybrid heterojunctions); the effect of microstructure; and the difference in the requirements upon binary and ternary heterojunctions to enable charge separation. A second aim is to improve understanding of luminescence based characterization techniques and find new applications of the techniques. In the context of dispeersed heterojunctions such as polymer:fullerene solar cells, luminescence allows us to study the effect of different recombination mechanisms and compare in particular recombination at the internal polymer:fullerene interface with recombination at the electrodes. This could prove to be a valuable diagnostic method for a range of optoelectronic devices. For example, luminescence applied in-situ to photovoltaic device sduring manufacture can serve as a diagostic tool to indicate the sources of energy loss within the device. We have engaged an indutrial project partner to explore this application.

As well as communicating the scientific progress of the research through publication of results in leading journals in material science, chemistry and physics, the team will communicate with a wider audience through public engagement activities and the media.
To access the general public we will use our experience in communicating science. Prof Nelson has ample recent experience in communicating research results through broadcast (for example interviews on Radio 4 'In Our Time' and Australian Broadcast Corporation's 'The Science Show' during 2012) and print (articles in The Guardian and Sublime Magazine during 2012) media. We will use our contacts in the media and with lay organisations to communicate the results of our research.

Lower cost photovoltaic technologies have a high potential for contribution to future power supply, particularly in the developing world and to carbon emissions mitigation. Prof Nelson leads the Sustainable Technologies and Options research theme at The Grantham Institute for Climate Change at Imperial College, which runs an active programme of seminars, briefing papers, discussions with policy makers and other stakeholders. During the last year she has presented research results on emerging PV technologies to members of government departments (DECC, DFID), the International Energy Agency, funding bodies, energy economists and science media. In addition Prof Nelson and Dr Ekins Daukes lead a programme of research into the mitigation potential of emerging photovoltaic technologies. They have agreed to write briefing papers for the Grantham Institute on the potential of solar power and on estimation of the mitigation potential of new renewable technologies. This provides a direct route to communicate significant results from this research to a wider energy and policy making community.

The Centre for Plastic Electronics (CPE) at Imperial is one of the five UK centres of excellence in PE and as such has access to the network of affiliated companies (such as Merck, BASF, Bayer, Solvay, hp, Cambridge Display Technology, Plastic Logic, Plextronics, Solar Press), government departments and research institutions that are active in developing devices and materials for organic electronics. Advances will be communicated via this network and other partners in the CPE and we will proactively pursue these relationships to exploit potential new developments and contribute to wealth generation.
Our research programme is directly relevant to companies seeking to develop organic photovoltaic devices. For this reason we have engaged Solar Press UK Ltd as a project partner, with the aim of evaluating the industrial use of our electroluminescence characterization technique in collaboration with them. Solar Press stand to benefit through early access to knowhow that can improve quality control and diagnostic testing of organic photovoltaics during production. In addition, through existing research collaborations we have direct contact with other companies working on commercializing novel photovoltaic technologies (Eight19, Oxford Photovoltaics, Molecular Photovoltaics,Tata Steel, G24i) and we will exploit these contacts to publicise the potential of the methods being developedin this programme. Direct contact with industry is also facilitated by the fact that Prof. Nelson is in regular contact with Solar Press as part of her Royal Society Industry Fellowship. Prof Nelson is also active within the Royal Society's Industry Fellows Network in seeking to build better pathways of communication between academia and industry. Finally, Prof Nelson is a co-opted member of the new EPSRC Supergen Solar Hub and as such has access to the UK academic and industrial community involved in solar energy technology.