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Full day modelling of V-shaped organic solar cell
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
Fraunhofer Institute Solar Energy Syst.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
2011 (English)In: Solar Energy, ISSN 0038-092X, Vol. 85, no 6, 1257-1263 p.Article in journal (Refereed) Published
Abstract [en]

Folded and planar solar cells are examined with optical simulations, with the finite element method. The maximum photocurrent densities during the full day are compared between cells of different geometries and tilting angles. The change of incident angle and spectrum over time are handled in this analysis. The results show that the light trapping effect of the folded cell makes these cells show higher maximum photocurrent densities than the planar cells during all hours of the day. This is the case for both single and tandem cells. The results also indicate that balancing the currents in the tandem cells by adjusting the active layer thickness may be more cumbersome with the folded tandem cells than the stacked planar cells.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam. , 2011. Vol. 85, no 6, 1257-1263 p.
Keyword [en]
Organic solar cell; Tandem cell; Light trapping
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-69881DOI: 10.1016/j.solener.2010.10.017ISI: 000291832600012OAI: diva2:433319
Available from: 2011-08-09 Created: 2011-08-08 Last updated: 2015-05-29
In thesis
1. Electron tomography and optical modelling for organic solar cells
Open this publication in new window or tab >>Electron tomography and optical modelling for organic solar cells
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Organic solar cells using carbon based materials have the potential to deliver cheap solar electricity. The aim is to be able to produce solar cells with common printing techniques on flexible substrates, and as organic materials can be made soluble in various solvents, they are well adapted to such techniques. There is a large variation of organic materials produced for solar cells, both small molecules and polymers. Alterations of the molecular structure induce changes of the electrical and optical properties, such as band gap, mobility and light absorption. During the development of organic solar cells, the step of mixing of an electron donor and an electron acceptor caused a leap in power conversion efficiency improvement, due to an enhanced exciton dissociation rate. Top performing organic solar cells now exhibit a power conversion efficiency of over 10%. Currently, a mix of a conjugated polymer, or smaller molecule, and a fullerene derivative are commonly used as electron donor and acceptor. Here, the blend morphology plays an important role. Excitons formed in either of the donor or acceptor phase need to diffuse to the vicinity of the donor-acceptor interface to efficiently dissociate. Exciton diffusion lengths in organic materials are usually in the order of 5-10 nm, so the phases should not be much larger than this, for good exciton quenching. These charges must also be extracted, which implies that a network connected to the electrodes is needed. Consequently, a balance of these demands is important for the production of efficient organic solar cells.

Morphology has been found to have a significant impact on the solar cell behaviour and has thus been widely studied. The aim of this work has been to visualize the morphology of active layers of organic solar cells in three dimensions by the use of electron tomography. The technique has been applied to materials consisting of conjugated polymers blended with fullerene derivatives. Though the contrast in these blends is poor, three-dimensional reconstructions have been produced, showing the phase formation in three dimensions at the scale of a few nanometres. Several material systems have been investigated and preparation techniques compared.

Even if excitons are readily dissociated and paths for charge extraction exist, the low charge mobilities of many materials put a limit on film thickness. Although more light could be absorbed by increased film thickness, performance is hampered due to increased charge recombination. A large amount of light is thus reflected and not used for energy conversion. Much work has been put into increasing the light absorption without hampering the solar cell performance. Aside from improved material properties, various light trapping techniques have been studied. The aim is here to increase the optical path length in the active layer, and in this way improve the absorption without enhanced extinction coefficient.

At much larger dimensions, light trapping in solar cells with folded configuration has been studied by the use of optical modelling. An advantage of these V-cells is that two materials with complementing optical properties may be used together to form a tandem solar cell, which may be connected in either serial or parallel configuration, with maintained light trapping feature. In this work optical absorption in V-cells has been modelled and compared to that of planar ones.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 63 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1414
Organic solar cells, Electron tomography, Optical modelling
National Category
Natural Sciences
urn:nbn:se:liu:diva-72903 (URN)978-91-7393-007-9 (ISBN)
Public defence
2012-02-03, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2011-12-13 Created: 2011-12-09 Last updated: 2012-01-03Bibliographically approved

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Andersson, ViktorInganäs, Olle
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Biomolecular and Organic ElectronicsFaculty of Science & EngineeringThe Institute of Technology
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