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

Lead Research Organisation: Imperial College London


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.

Planned Impact

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.


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Description So far, we have discovered how the performance of organic and hybrid solar cells can be understood by studying the light emitted by the device when it is operated as a light emitting diode. We have been able to relate the energy of states at the donor:acceptor inteface to the emitted light using experiment and calculations. We have developed a new method to quantify the losses in the open ciruit voltage of different types of solar cell.
Exploitation Route The methods and quantitative results are relevant to other solar cell researchers and potentially to companies developing printable solar cells.
The methods are being used quite widely in the academic community now (in 2019) and heve helped to enable follow-on funding.
Sectors Electronics,Energy,Environment

Description PhD student Jizhong Yao who worked on this project has started a company, Microquanta Semiconductor, in China after successfully applying for a grant from regional government in China. In January 2017 his company succeeded in setting a new world record for efficiency of photovoltaic mini-modules based on perovskite semiconductor materials. He had used knowledge obtained during his PhD to make the breakthrough. This was followed by further mini-module improvements during 2018 - 2022. Moreover, the work has had substantial academic impact in the research community, with other groups now evaluating solar cell performance in a similar manner, and making similar assessment of the radiative efficiency of devices.
Sector Electronics,Energy,Environment
Impact Types Economic

Description Application Targeted and Integrated Photovoltaics - Enhancing UK Capability in Solar
Amount £5,991,738 (GBP)
Funding ID EP/T028513/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 06/2020 
End 06/2025
Description Designing conjugated polymers for photocatalysis and ion transport (CAPaCITy)
Amount € 2,300,000 (EUR)
Funding ID 742708 
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 09/2017 
End 09/2022
Description EPSRC
Amount £44,234 (GBP)
Funding ID Imperial Knowledge Transfer Secondment fund 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2014 
End 03/2015
Description EPSRC Grand Challenge
Amount £1,035,857 (GBP)
Funding ID EP/M025020/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 07/2016 
End 07/2018
Description FZ Juelich - EL grant 
Organisation Julich Research Centre
Country Germany 
Sector Academic/University 
PI Contribution Collaboration with Prof Thomas Kirchartz on measurement planning, data analysis and modelling
Collaborator Contribution Provision of data for analysis and modelling. Co-authorship of papers.
Impact Several papers listed under the grant outputs
Start Year 2013