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In situ reflectance imaging of organic thin film formation from solution deposition
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology.ORCID iD: 0000-0001-9229-2028
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2013 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 114, 89-98 p.Article in journal (Refereed) Published
Abstract [en]

In this work we present reflectance imaging as a suitable method for in situ monitoring of the drying process of film formation for organic photovoltaics (OPV) over large areas, as well as for lab-scale spin-coating. The drying wet film is illuminated with a narrow bandwidth LED with the specularly reflected light recorded by a video camera as the film dries and forms the active layer of the OPV cell. The interference fringes generated by the thinning wet film can be used to measure the rate of solvent evaporation and the drying time. Subsequent mapping elucidates variations in drying conditions over the substrate, which lead to variations in morphology formation. The technique is suitable for tracking thickness variations of the dry film, with a sensitivity of 10 nm, by comparing the intensity of the reflected light from the dry film to simulated interference conditions calculated for each thickness. The drying process is furthermore accurately simulated by an optical model considering the changes in refractive index as the amount of solvent decreases with respect to the solid content. This non-invasive in situ method represents an important monitoring tool for future large scale OPV manufacturing where high performing morphologies with uniform thickness have to be formed over very large areas.

Place, publisher, year, edition, pages
Elsevier , 2013. Vol. 114, 89-98 p.
Keyword [en]
Reflectance imaging, Process control, Blade coating, Spin coating, Evaporation, OPV
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-95498DOI: 10.1016/j.solmat.2013.02.030ISI: 000319486700013OAI: oai:DiVA.org:liu-95498DiVA: diva2:635788
Note

Funding Agencies|Knut and Alice Wallenberg foundation||Swedish Energy Agency||

Available from: 2013-07-05 Created: 2013-07-05 Last updated: 2017-12-06
In thesis
1. Optoelectrical Imaging Methods for Organic Photovoltaic Materials and Moduls
Open this publication in new window or tab >>Optoelectrical Imaging Methods for Organic Photovoltaic Materials and Moduls
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To achieve a high living standard for all people on Earth access to low cost energy is essential. The massive burning of fossil fuels must be drastically reduced if we are to avoid large changes of our climate. Solar cells are both technologically mature and have the potential to meet the huge demand for renewable energy in many countries. The prices for silicon solar cells have decreased rapidly during the course of this thesis and are now in grid parity in many countries.

However, the potential for even lower energy costs has driven the research on polymer solar cells, a class of thin film solar cells. Polymer solar cells can be produced by roll to roll printing which potentially enables truly low cost solar cells. However, much research and development remain to reach that target.

Polymer solar cells consist of a semiconducting composite material sandwiched between two electrodes, of which one is transparent, to let the light energy in to the semiconductor where it is converted to electric energy. The semiconductor comprise an intimate blend of polymer and fullerenes, where the nanostructure of this blend is crucial for the photo current extraction.

To reach higher solar cell performance the dominating strategy is development and fine tuning of new polymers. To estimate their potential as solar cell materials their optical response have been determined by spectroscopic ellipsometry. Furthermore, optical simulations have been performed where the direction dependency of the optical response of the transparent electrode material PEDOT:PSS have been accounted for. The simulations show reduced electrode losses for light incident at large oblique angles.

Moreover, we have shown that a gentle annealing of the active layer induces a local conformational changes of an amorphous polymer that is beneficial for solar cell performance. The active layer is deposited from solution where the drying kinetics determine the final nanostructure. We have shown that using in-situ photoluminescence phase separation can be detected during the drying process while a reflectance method have been developed to image lateral variations of solvent evaporation rate.

Imaging methods are important tools to detect performance variations over the solar cell area. For this purpose an intermodulation based photo current imaging method have been developed to qualitatively differentiate the major photo current loss mechanisms. In addition, a 1D LED-array photo current imaging method have been developed and verified for high speed in-line characterization of printed organic solar modules.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 60 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1712
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-123035 (URN)10.3384/diss.diva-123035 (DOI)978-91-7685-923-0 (ISBN)
Public defence
2015-12-17, Planck, Fysikhuset, Campus Valla, Linköping, 13:15 (English)
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Supervisors
Note

The corrections in the published errata list are implemented in the electronic version.

Available from: 2015-12-03 Created: 2015-12-02 Last updated: 2016-01-14Bibliographically approved

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Bergqvist, JonasMauger, ScottTvingstedt, KristoferArwin, HansInganäs, Olle

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