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New method for lateral mapping of bimolecular recombination in thin film organic solar cells
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
Laboratory of Photonics and Interfaces, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
Nanostructure Physics, KTH Royal Institute of Technology, Stockholm, Sweden.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
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2016 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 24, no 8, 1096-1108 p.Article in journal (Refereed) Published
Abstract [en]

The best organic solar cells are limited by bimolecular recombination. Tools to study these losses are available; however, they are only developed for small area (laboratory-scale) devices and are not yet available for large area (production-scale) devices. Here we introduce the Intermodulation Light Beam-Induced Current (IMLBIC) technique, which allows simultaneous spatial mapping of both the amount of extracted photocurrent and the bimolecular recombination over the active area of a solar cell. We utilize the second-order non-linear dependence on the illumination intensity as a signature for bimolecular recombination. Using two lasers modulated with different frequencies, we record the photocurrent response at each modulation frequency and the bimolecular recombination in the second-order intermodulation response at the sum and difference of the two frequencies. Drift-diffusion simulations predict a unique response for different recombination mechanisms. We successfully verify our approach by studying solar cells known to have mainly bimolecular recombination and thus propose this method as a viable tool for lateral detection and characterization of the dominant recombination mechanisms in organic solar cells. We expect that IMLBIC will be an important future tool for characterization and detection of recombination losses in large area organic solar cells.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016. Vol. 24, no 8, 1096-1108 p.
Keyword [en]
Organic photovoltaics, imaging, photocurrent, bimolecular recombination, light beam induced current, LBIC, intermodulation
National Category
Physical Sciences
URN: urn:nbn:se:liu:diva-123033DOI: 10.1002/pip.2770ISI: 000380164100007OAI: diva2:876158

Funding agencies|Swedish Research Council; Swedish Energy Agency; the Knut and Alice Wallenberg foundation through a Wallenberg Scholar grant to O.I

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-12-02 Created: 2015-12-02 Last updated: 2016-09-19Bibliographically approved
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.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1712
National Category
Physical Sciences
urn:nbn:se:liu:diva-123035 (URN)10.3384/diss.diva-123035 (DOI)978-91-7685-923-0 (print) (ISBN)
Public defence
2015-12-17, Planck, Fysikhuset, Campus Valla, Linköping, 13:15 (English)

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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