Ageing of printable polymer solar cells
Lead Research Organisation:
University of St Andrews
Department Name: Physics and Astronomy
Abstract
Solar power is by far the most abundant renewable energy source. However, at present its use is limited by the high cost of solar cells, so that we continue to obtain most of our power from fossil fuels. Polymer (plastic) solar cells are an exciting research field that aims to address this problem, as polymer solar cells could be made by simple manufacturing processes such as roll to roll coating. The result would be much lower cost solar cells, with much lower energy of production. Most research to date has focussed on the efficiency of such solar cells, and good progress has been made, leading to efficiencies approximately two thirds of commercial amorphous silicon solar cells.In this proposal we address the most important remaining issue, namely understanding and enhancing the lifetime of polymer solar cells. To do this we will combine advanced photophysical, morphological and chemical analysis of solar cells before, during and after operation to gain new insight into the factors controlling degradation of such cells. This will provide a solid foundation for developing strategies for extending the solar cell lifetime in the later part of the project.The operation of polymer solar cells depends critically on the nanometre scale arrangement of the materials, so we will use sophisticated electron tomography techniques to study the nanoscale morphology and how it changes with device operation. This will be complemented by optical and electronic measurements performed in-situ on operating solar cells. A further innovation will be to make nanoscale perforation of an encapsulation layer and combine it with electron beam techniques to study local degradation with nanometre resolution. This challenging programme requires collaboration between world-leading research groups in St Andrews, Changchun, and Glasgow to access the range of expertise and facilities to make major progress, and will lead to a new UK-China collaboration.
Planned Impact
Economic and Societal Impact The proposed research has significant potential for societal, commercial and academic impact. Renewable energy is a global issue and it is no overstatement to declare that our existence depends on a step-change in provision and attitude towards sustainable alternatives to fossil fuels. Significant changes in this direction will need to be met by a collection of technologies - e.g. solar (heating and photovoltaics), wind, tidal, nuclear, biomass/biofuels, ground and air source heating - to target the full range of consumers (i.e. commercial and private/domestic use). At present the use of solar photovoltaics is extremely limited because the cost is much higher than for electricity generated by burning fossil fuels, so the key challenge is to reduce the cost. The simple fabrication at low temperature of organic photovoltaic (OPV) devices, and in particular polymer solar cells, provides a promising route to achieving this and impressive progress towards demonstrations of roll to roll manufacturing is being made. This in turn brings into focus the need to develop an understanding of degradation mechanisms in such devices and identify the best materials and architectures for stable devices. Communications and Engagement After patenting any inventions arising from the project we are keen to present our results to companies as well as to other academics. We also foresee tremendous opportunities for public engagement. In addition to presenting results at major academic meetings such as MRS, we will also present at meetings with a more industrial bias (including those of the Photonics and Plastic Electronics KTN). We will of course disseminate our results through the scientific literature, targeting leading journals such as Advanced Materials. We are excited about the potential for public engagement that this project will bring, and plan to involve the appointed researchers (and ourselves) in public engagement activities. Collaboration and Exploitation A key strength of the project is the complementary skills of the teams in St Andrews, Changchun and Glasgow. As explained in the proposal, we will make the most of these capabilities via face to face meetings every six months, monthly videoconferences and exchange of researchers. All the investigators have considerable experience of filing patents, many of which have been granted and/or licensed. IDWS has recent experience of both licensing and spin-out routes to commercialise several organic semiconductor inventions. This experience will be invaluable for recognising and implementing the most appropriate exploitation route for results arising from the project. The exploitation route will take account of the status of the technology and associated IP, the potential markets and the possible routes to those markets. It is likely to involve collaboration with companies, and the most appropriate choice depends on the nature of the innovation. Candidates include the project partners Konarka and ECN (see letters of support), as well as Merck (Southampton), SolarPress (London) and Polysolar (Cambridge). Professional support is available from the Research and Enterprise departments of the Universities and via the Knowledge Exchange Office of the Scottish Universities Physics Alliance. We plan to put in place a collaboration agreement at the start of the project which defines partner responsibilities, distribution of finances and agreed mechanisms for knowledge exchange and the protection and exploitation of IP.
People |
ORCID iD |
Ifor Samuel (Principal Investigator) | |
Joachim Loos (Co-Investigator) |
Publications
Alekseev A
(2015)
Morphology and local electrical properties of PTB7:PC 71 BM blends
in Journal of Materials Chemistry A
Alekseev A
(2014)
Three-dimensional imaging of polymer materials by Scanning Probe Tomography
in European Polymer Journal
Hedley GJ
(2013)
Determining the optimum morphology in high-performance polymer-fullerene organic photovoltaic cells.
in Nature communications
Description | Key findings in this project included detailed understanding of the correlation between the spatial organisation, interactions with light and device performance of printable polymer solar cell blends. We worked with collaborators at the Changchun Institute of Applied Chemistry in China who developed large-area deposition techniques to enable printing of polymer solar cells. Ageing of polymer solar cells will alter the morphology (spatial arrangement) of the blend, so we have developed a number of techniques including atomic force microscopy, transmission electron microscopy and photoconductive atomic force microscopy to observe the morphology of the blend. These techniques were applied to a number of solar cell blends to understand how the morphology, photophysics and device performance all depend upon each other. Working with a high performance polymer/fullerene blend we investigated these parameters, uncovering how the materials arranged themselves at the nanoscale using ultrafast photophysics and atomic force microscopy. We used photoluminescence emitted from the blend to understand how quickly absorbed light is converted into charge-pairs by measuring the photoluminescence as a function of time. We were also able to use the time-resolved photoluminescence as a nanoscale "ruler" to determine the sizes of the domains of the material in the blend. These results were in very good agreement with atomic force microscopy measurements that we made. To see very subtle alterations in blend mixing we used photoconductive atomic force microscopy to discriminate between the polymer and the fullerene, observing nanoscale ordering of the materials. A number of different deposition techniques were studied, including doctor-blade, spray-coating and screen-printing. Deposition of blends with these different deposition techniques was completed in Changchun along with device testing, while samples were sent to St Andrews and Glasgow for morphology and photophysics measurements. It was found that while the morphology can vary greatly with different deposition techniques (variation in organisational length scales from nanometres to microns) the time-resolve photoluminescence measurements tell us that good harvesting of light into charges still occurs. This finding agrees with the measured performance of devices, where power conversion efficiencies ~ 5% were achieved with 10x10 cm large-area devices. This program of work has enabled us to understand what governs efficiencies when using different large-area deposition techniques that are compatible with printing. |
Sectors | Energy |
Description | This outcome describes the scientific impact of the work that has been produced in this grant. The work has aided significantly to the understanding of what governs device efficiency in plastic solar cells. The impact is scientific and crosses disciplines in the material science community. By combining measurement techniques on photophysics, morphology and devices this work has enabled gains in understanding that are greater than the sum of its parts. Demonstrable impact has been achieved with our article published in Nature Communications, where we performed advanced ultrafast fluorescence measurements and photoconductive atomic force microscopy to reconstruct the nanoscale spatial organisation of the polymer and fullerene materials in a plastic solar cell blend. The organic semiconductor and material science communities are seeking understanding of what spatial organisations of the materials enables high photovoltaic efficiencies, and we were able to determine that thin elongated fibre-like stands rich in each material enable good conversion of light into free charges, while also maximising the pathways to extract the charge out of the device for power extraction. Application of the technique of photoconductive atomic force microscopy to plastic solar cell blends is also impactful, as this has very rarely been done before, and we have demonstrated that it can be used as a very sensitive probe on subtle variations in mixing between two materials in a blend. Our work with large-area deposition of blends has also proved impactful in exploring how such a wide variety of deposition techniques leads to quite different morphologies, yet similar photophysics and device performance. Beneficiaries: Material science community, organic semiconductor community Contribution Method: This research contributed to the UK and global research base by enabling new advances in measuring the morphology of high performance plastic solar cells and understanding of how device performance depends upon it. Such outcomes will contribute to the knowledge of plastic solar cells and enable future advancements. We have also examined how large-area printable plastic solar cells can be realised by looking at a number of deposition techniques, which will contribute towards large-area commercialisation of this technology. |
Sector | Chemicals,Energy |
Impact Types | Societal |
Description | Collaboration with Changchun Institute of Applied Chemistry, China |
Organisation | Changchun Institute of Applied Chemistry |
Country | China |
Sector | Academic/University |
PI Contribution | We have established a wide-ranging collaboration with the group of Prof. Xiaoniu Yang at the Changchun Institute of Applied Chemistry in China. Prof. Yang has developed a large range of techniques to print large-area polymer solar cells, fabricate and test devices. We have built an extensive scientific program to bring together large-area fabrication, measurement of devices, photophysics and morphology to enable better understanding printed polymer solar cells. This collaboration has involved regular communication by telephone conference as well as visits to each other?s institutions to enable skillset enhancement for both parties. We shall continue this collaboration beyond the end of this grant. This collaboration has enabled a significant enhancement to my research. The group of Prof. Yang has world-leading expertise in the fabrication of large-area printed polymer solar cells, and this collaboration has enabled me to obtain insights and access to valuable expertise/samples. |
Start Year | 2011 |
Description | Collaboration with University of Glasgow |
Organisation | University of Glasgow |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | We have established a new collaboration with scanning probe microscopy expertise at the University of Glasgow. This has enabled valuable scientific outcomes on using advanced atomic force microscopy and transmission electron microscopy on polymer solar cells. This collaboration has involved regular communication by telephone conference as well as visits to each other?s institutions to enable skillset enhancement for both parties. We shall continue this collaboration beyond the end of this grant, continuing to work with the PDRA Dr Alexander Aleeksev, who is now a permanent member of staff at Nazarbayev University, Kazakhstan. This collaboration has proven invaluable in bringing together very valuable skillsets in scanning probe microscopy with ultrafast photophysics. This unique combination of techniques has enabled some very valuable results to be reported, and this collaboration will continue with Dr Aleeksev. |
Start Year | 2011 |