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Tvingstedt, Kristofer
Publications (10 of 37) Show all publications
Bergqvist, J., Mauger, S., Tvingstedt, K., Arwin, H. & Inganäs, O. (2013). In situ reflectance imaging of organic thin film formation from solution deposition. Solar Energy Materials and Solar Cells, 114, 89-98
Open this publication in new window or tab >>In situ reflectance imaging of organic thin film formation from solution deposition
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2013 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 114, p. 89-98Article 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
Keywords
Reflectance imaging, Process control, Blade coating, Spin coating, Evaporation, OPV
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-95498 (URN)10.1016/j.solmat.2013.02.030 (DOI)000319486700013 ()
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
Bergqvist, J., Tvingstedt, K., Arwin, H. & Inganäs, O. (2012). In situ reflectance imaging of organic thin film formation from solution. Paper presented at The 4th international Conference on Hybrid and Organic Photovoltaics, HOPV12, May 6-9, 2012, Uppsala.
Open this publication in new window or tab >>In situ reflectance imaging of organic thin film formation from solution
2012 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

The rapid progress of organic photovoltaic devices during the last decade, with power conversion efficiencies now exceeding 8%, has brought the technology close to an industrial breakthrough. For polymer solar cells, roll to roll printing is desired to gain the production advantage. The formation of the photoactive material from solutions needs to be controlled and optimized. Therefore a suitable method to monitor the deposition process is needed as deviations of drying times1 and drying rates2 during the coating process have proven to generate morphology variations causing variations in photocurrent generation.

Here we demonstrate how reflectance imaging can be used to monitor the drying process, both for spin coating and blade coating deposition. A blue LED is used as light source to generate specular reflections imaged by a CMOS camera. The thinning of the wet film can then be observed by thin film interference, and can be recorded for each pixel. This enables an estimation of the evaporation rate for each pixel mapped over the substrate. For spin coating the evaporation rate is shown to increase with the distance from the rotation center, whereas the air flow is the determining parameter during blade coating. By mapping the times when interference ceases, lateral variations in drying time are visualized. Furthermore the quenching of polymer photoluminescence during the drying process can be visualized, thus creating a possibility to estimate morphological variations. Moreover lateral thickness variations of the dry film can be visualized by scanning ellipsometry. After depositing a top electrode photocurrent images can be generated by a laser scanning method. This allows for a direct comparison of drying conditions and photocurrent generation.  The possibility to monitor the thin film formation as well as lateral variations in thickness in-situ by a non-invasive method, is an important step for future large scale applications where stable high performing generating morphologies have to be formed over large areas.

1Schmidt-Hansberg, B.; Sanyal, M.; Klein, M.F.G.; Pfaff, M.; Schnabel, N.; Jaiser, S.; Vorobiev, A.; Müller, E.; Colsmann, A.; Scharfer, P.; Gerthsen, D.; Lemmer, U.; Barrena, E.; and Schabel, W., ACS Nano 5 , 2011, 8579-8590

2 Hou, L.; Wang, E.; Bergqvist, J.; Andersson, V.B.; Wang, Z.; Müller, C.; Campoy-Quiles, M.; Andersson, M.R.; Zhang, F.; Inganäs, O.,Adv. Func. Mat. 21 , 2011, 3169–3175

National Category
Energy Systems
Identifiers
urn:nbn:se:liu:diva-86726 (URN)
Conference
The 4th international Conference on Hybrid and Organic Photovoltaics, HOPV12, May 6-9, 2012, Uppsala
Available from: 2012-12-28 Created: 2012-12-28 Last updated: 2013-10-14
Tang, Z., Andersson, M., George, Z., Vandewal, K., Tvingstedt, K., Heriksson, P., . . . Inganäs, O. (2012). Interlayer for Modified Cathode in Highly Efficient Inverted ITO-Free Organic Solar Cells. Advanced Materials, 24(4), 554-558
Open this publication in new window or tab >>Interlayer for Modified Cathode in Highly Efficient Inverted ITO-Free Organic Solar Cells
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2012 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 24, no 4, p. 554-558Article in journal (Refereed) Published
Abstract [en]

Inverted polymer solar cells with a bottom metal cathode modified by a conjugated polymer interlayer show considerable improvement of photocurrent and fill factor, which is due to hole blocking at the interlayer, and a modified surface energy which affects the nanostructure in the TQ1/[70]PCBM blend.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-74183 (URN)10.1002/adma.201104579 (DOI)
Available from: 2012-01-20 Created: 2012-01-20 Last updated: 2017-12-08
Tvingstedt, K., Tang, Z. & Inganäs, O. (2012). Light trapping with total internal reflection and transparent electrodes in organic photovoltaic devices. Applied Physics Letters, 101(16)
Open this publication in new window or tab >>Light trapping with total internal reflection and transparent electrodes in organic photovoltaic devices
2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 16Article in journal (Refereed) Published
Abstract [en]

Herein, we demonstrate a method to build highly efficient light trapping structures for printed organic solar cells and modules, compatible with roll to roll manufacturing. Echelle grating structures in combination with semitransparent electrodes allow for efficient light trapping via means of total internal reflection. With this method, we demonstrate an increased cell photocurrent response up to 24%, compared to a standard cell configuration with a planar reflector. The demonstrated light trapping approach is expected to be even more useful for photovoltaic modules, where light hitting "dead areas" in between the sub-cells comprising the module will now be utilized.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87228 (URN)10.1063/1.4759125 (DOI)000310669300075 ()
Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2017-12-06
Vandewal, K., Tvingstedt, K. & Inganäs, O. (2012). Polarization anisotropy of charge transfer absorption and emission of aligned polymer: fullerene blend films. Physical Review B. Condensed Matter and Materials Physics, 86(3), 035212
Open this publication in new window or tab >>Polarization anisotropy of charge transfer absorption and emission of aligned polymer: fullerene blend films
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 3, p. 035212-Article in journal (Refereed) Published
Abstract [en]

An improved understanding of the electronic structure of interfacial charge transfer (CT) states is of importance due to their crucial role in charge carrier generation and recombination in organic donor-acceptor (DA) solar cells. DA combinations with a small difference between the energy of the CT state (E-CT) and energy of the donor exciton (E-D*) are of special interest since energy losses due to electron transfer are minimized, resulting in an optimized open-circuit voltage. In that case, the CT state can be considered as a resonance mixture, containing character of a fully ionic state (D+ A(-)) and of the local polymer excited state (D* A). We show that the D* A contribution to the overall CT state wave function can be determined by measurements of the polarization anisotropy of CT absorption and emission of polymer: fullerene blends with aligned polymer chains. We study two donor polymers, P3HT and TQ1, blended with fullerene acceptors with different ionization potentials, allowing variation of the E-D* -E-CT difference. We find that, upon decreasing E-D* -E-CT, the local excitonic D* A character of the CT state increases, resulting in a decreased fraction of charge transferred and an increased transition dipole moment. For typical polymer: fullerene systems, this effect is expected to become detrimental for device performance if E-D* - E-CT andlt; 0.1 eV. This however, depends on the electronic coupling between D* A and D+ A(-), which we experimentally estimate to be similar to 6 meV for the TQ1: PCBM system.

Place, publisher, year, edition, pages
American Physical Society, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-81833 (URN)10.1103/PhysRevB.86.035212 (DOI)000306924500006 ()
Note

Funding Agencies|Swedish Energy Agency||Swedish Research Council||VINNOVA||Knut and Alice Wallenberg foundation||

Available from: 2012-09-25 Created: 2012-09-24 Last updated: 2017-12-07
Vandewal, K., Ma, Z., Bergqvist, J., Tang, Z., Wang, E., Henriksson, P., . . . Inganäs, O. (2012). Quantification of Quantum Efficiency and Energy Losses in Low Bandgap Polymer:Fullerene Solar Cells with High Open-Circuit Voltage. Advanced Functional Materials, 22(16), 3480-3490
Open this publication in new window or tab >>Quantification of Quantum Efficiency and Energy Losses in Low Bandgap Polymer:Fullerene Solar Cells with High Open-Circuit Voltage
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2012 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 22, no 16, p. 3480-3490Article in journal (Refereed) Published
Abstract [en]

In organic solar cells based on polymer:fullerene blends, energy is lost due to electron transfer from polymer to fullerene. Minimizing the difference between the energy of the polymer exciton (ED*) and the energy of the charge transfer state (ECT) will optimize the open-circuit voltage (Voc). In this work, this energy loss ED*-ECT is measured directly via Fourier-transform photocurrent spectroscopy and electroluminescence measurements. Polymer:fullerene photovoltaic devices comprising two different isoindigo containing polymers: P3TI and PTI-1, are studied. Even though the chemical structures and the optical gaps of P3TI and PTI-1 are similar (1.4 eV1.5 eV), the optimized photovoltaic devices show large differences in Voc and internal quantum efficiency (IQE). For P3TI:PC71BM blends a ED*-ECT of similar to 0.1 eV, a Voc of 0.7 V and an IQE of 87% are found. For PTI-1:PC61BM blends an absence of sub-gap charge transfer absorption and emission bands is found, indicating almost no energy loss in the electron transfer step. Hence a higher Voc of 0.92 V, but low IQE of 45% is obtained. Morphological studies and field dependent photoluminescence quenching indicate that the lower IQE for the PTI-1 system is not due to a too coarse morphology, but is related to interfacial energetics. Losses between ECT and qVoc due to radiative and non-radiative recombination are quantified for both material systems, indicating that for the PTI-1:PC61BM material system, Voc can only be increased by decreasing the non-radiative recombination pathways. This work demonstrates the possibility of obtaining modestly high IQE values for material systems with a small energy offset (andlt;0.1 eV) and a high Voc.

Place, publisher, year, edition, pages
Wiley-VCH Verlag Berlin, 2012
Keywords
organic solar cell, fullerene, conjugated polymer, charge transfer state
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-82067 (URN)10.1002/adfm.201200608 (DOI)000307566200016 ()
Note

Funding Agencies|Swedish Energy Agency||Swedish Research Council (VR)||VINNOVA||Knut and Alice Wallenberg foundation||

Available from: 2012-10-01 Created: 2012-09-28 Last updated: 2017-12-07
Tang, Z., George, Z., Ma, Z., Bergqvist, J., Tvingstedt, K., Vandewal, K., . . . Inganäs, O. (2012). Semi-Transparent Tandem Organic Solar Cells with 90% Internal Quantum Efficiency. ADVANCED ENERGY MATERIALS, 2(12), 1467-1476
Open this publication in new window or tab >>Semi-Transparent Tandem Organic Solar Cells with 90% Internal Quantum Efficiency
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2012 (English)In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 2, no 12, p. 1467-1476Article in journal (Refereed) Published
Abstract [en]

Semi-transparent (ST) organic solar cells with potential application as power generating windows are studied. The main challenge is to find proper transparent electrodes with desired electrical and optical properties. In this work, this is addressed by employing an amphiphilic conjugated polymer PFPA-1 modified ITO coated glass substrate as the ohmic electron-collecting cathode and PEDOT:PSS PH1000 as the hole-collecting anode. For active layers based on different donor polymers, considerably lower reflection and parasitic absorption are found in the ST solar cells as compared to solar cells in the standard geometry with an ITO/PEDOT:PSS anode and a LiF/Al cathode. The ST solar cells have remarkably high internal quantum efficiency at short circuit condition (similar to 90%) and high transmittance (similar to 50%). Hence, efficient ST tandem solar cells with enhanced power conversion efficiency (PCE) compared to a single ST solar cell can be constructed by connecting the stacked two ST sub-cells in parallel. The total loss of photons by reflection, parasitic absorption and transmission in the ST tandem solar cell can be smaller than the loss in a standard solar cell based on the same active materials. We demonstrate this by stacking five separately prepared ST cells on top of each other, to obtain a higher photocurrent than in an optimized standard solar cell.

Place, publisher, year, edition, pages
Wiley-VCH Verlag Berlin, 2012
Keywords
polymer solar cells, semi-transparent solar cells, interface, conjugated polymers, tandem solar cells
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-86894 (URN)10.1002/aenm.201200204 (DOI)000312035800008 ()
Note

Funding Agencies|Swedish Energy Agency||Swedish Research Council||Advanced Functional Materials initiative at Linkoping University||Knut and Alice Wallenberg Foundation (KAW)||KAW||VINNOVA||

Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2015-05-29
Vandewal, K., Tvingstedt, K. & Inganäs, O. (2011). Charge Transfer States in Organic Donor-Acceptor Solar Cells. Semiconductors and semimetals, 85, 261-295
Open this publication in new window or tab >>Charge Transfer States in Organic Donor-Acceptor Solar Cells
2011 (English)In: Semiconductors and semimetals, ISSN 0080-8784, Vol. 85, p. 261-295Article in journal (Refereed) Published
Abstract [en]

For an efficient conversion of photons to electrons by organic materials used for photovoltaic applications, the presence of a material interface between an electron-donating and electron-accepting material is crucial. This chapter deals with the interfacial charge transfer states formed at such interfaces under solar illumination. Absorption of long-wavelength light, with energy lower than the optical gap of both donor and acceptor results in the direct formation of these charge transfer states. Decay of CT states to the ground state will result in weak light emission. Both CT absorption and emission will be linked to photovoltaic performance. The role of the CT state in determining the open-circuit voltage is discussed in detail. We will also elaborate on the efficiency of dissociation and photocurrent generation from thermally relaxed CT states. Based on thermodynamical considerations and in the absence of nonradiative recombination, upper limits for the efficiency of organic solar cells based on donor–acceptor interfaces are derived and possible improvements and future research directions are indicated.

Place, publisher, year, edition, pages
Academic Press, 2011
Keywords
conjugated polymer
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-76218 (URN)10.1016/B978-0-12-391060-8.00008-3 (DOI)000299294900008 ()
Note

Classified as article and book chapter in Web of Science.

ISBN (Book): 978-0-12-391060-8

Available from: 2012-03-30 Created: 2012-03-30 Last updated: 2017-12-07Bibliographically approved
O Reese, M., Gevorgyan, S. A., Jorgensen, M., Bundgaard, E., Kurtz, S. R., Ginley, D. S., . . . C Krebs, F. (2011). Consensus stability testing protocols for organic photovoltaic materials and devices. SOLAR ENERGY MATERIALS AND SOLAR CELLS, 95(5), 1253-1267
Open this publication in new window or tab >>Consensus stability testing protocols for organic photovoltaic materials and devices
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2011 (English)In: SOLAR ENERGY MATERIALS AND SOLAR CELLS, ISSN 0927-0248, Vol. 95, no 5, p. 1253-1267Article in journal (Refereed) Published
Abstract [en]

Procedures for testing organic solar cell devices and modules with respect to stability and operational lifetime are described. The descriptions represent a consensus of the discussion and conclusions reached during the first 3 years of the international summit on OPV stability (ISOS). The procedures include directions for shelf life testing, outdoor testing, laboratory weathering testing and thermal cycling testing, as well as guidelines for reporting data. These procedures are not meant to be qualification tests, but rather generally agreed test conditions and practices to allow ready comparison between laboratories and to help improving the reliability of reported values. Failure mechanisms and detailed degradation mechanisms are not covered in this report.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
Keywords
Stability, Lifetime, Testing, Protocol, Reporting
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-68680 (URN)10.1016/j.solmat.2011.01.036 (DOI)000290359200003 ()
Available from: 2011-05-27 Created: 2011-05-27 Last updated: 2011-05-30
Muller, C., Bergqvist, J., Vandewal, K., Tvingstedt, K., Anselmo, A. S., Magnusson, R., . . . Inganäs, O. (2011). Phase behaviour of liquid-crystalline polymer/fullerene organic photovoltaic blends: thermal stability and miscibility. Journal of Materials Chemistry, 21(29), 10676-10684
Open this publication in new window or tab >>Phase behaviour of liquid-crystalline polymer/fullerene organic photovoltaic blends: thermal stability and miscibility
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2011 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 29, p. 10676-10684Article in journal (Refereed) Published
Abstract [en]

The thermal behaviour of an organic photovoltaic (OPV) binary system comprised of a liquid-crystalline fluorene-based polymer and a fullerene derivative is investigated. We employ variable-temperature ellipsometry complemented by photo-and electroluminescence spectroscopy as well as optical microscopy and scanning force nanoscopy to explore phase transitions of blend thin films. The high glass transition temperature correlates with the good thermal stability of solar cells based on these materials. Furthermore, we observe partial miscibility of the donor and acceptor together with the tendency of excess fullerene derivative to segregate into exceedingly large domains. Thus, for charge generation less adequate bulk-heterojunction nanostructures are poised to develop if this mixture is exposed to more elevated temperatures. Gratifyingly, the solubility of the fullerene derivative in the polymer phase is found to decrease if a higher molecular-weight polymer fraction is employed, which offers routes towards improving the photovoltaic performance of non-crystalline OPV blends.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-69930 (URN)10.1039/c1jm11239b (DOI)000292978600016 ()
Available from: 2011-08-09 Created: 2011-08-08 Last updated: 2017-12-08
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