| 1. |
- Andersson, Mattias, et al.
(författare)
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Unified Study of Recombination in Polymer:Fullerene Solar Cells Using Transient Absorption and Charge-Extraction Measurements
- 2013
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society. - 1948-7185 .- 1948-7185. ; 4:12, s. 2069-2072
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Tidskriftsartikel (refereegranskat)abstract
- Recombination in the well-performing bulk heterojunction solar cell blend between the conjugated polymer TQ-1 and the substituted fullerene PCBM has been investigated with pump-probe transient absorption and charge extraction of photo-generated carriers (photo-CELIV). Both methods are shown to generate identical and overlapping data under appropriate experimental conditions. The dominant type of recombination is bimolecular with a rate constant of 7 x 10(-12) cm(-3) s(-1). This recombination rate is shown to be fully consistent with solar cell performance. Deviations from an ideal bimolecular recombination process, in this material system only observable at high pump fluences, are explained with a time-dependent charge-carrier mobility, and the implications of such a behavior for device development are discussed.
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| 2. |
- De, Swati, et al.
(författare)
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Exciton Dynamics in Alternating Polyfluorene/Fullerene Blends
- 2008
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Ingår i: Journal of Chemical Physics. - College Park, MD, United States : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 350:1-3, s. 14-22
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Tidskriftsartikel (refereegranskat)abstract
- Exciton dynamics in alternating copolymer/fullerene solar cell blends have been investigated using femtosecond transient absorption spectroscopy. The acceptor concentrations have been varied over a wide range. Experimental data, kinetic modeling and simulations, all indicate that the efficiency of exciton conversion to charges is 100% even at acceptor concentrations as low as 20 wt%. The reported dependence of solar cell efficiency on fullerene concentration may thus arise from other factors. However, there exists an acceptor concentration threshold (5 wt%) below which a substantial fraction of the excitations remain unquenched. The results, we believe are very relevant to optimization of performance efficiency by clever manipulation of morphology. We have also observed exciton–exciton energy transfer in these blends at low acceptor concentrations.
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| 3. |
- De, Swati, et al.
(författare)
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Geminate charge recombination in alternating polyfluorene copolymer/fullerene blends
- 2007
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 129:27, s. 8466-8472
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Tidskriftsartikel (refereegranskat)abstract
- By measuring excited state and charge dynamics in blends of an alternating polyfluorene copolymer and fullerene derivative over nine orders in time and two orders in light intensity, we have monitored the light-induced processes from ultrafast charge photogeneration to much slower decay of charges by recombination. We find that at low light intensities relevant to solar cell operation relatively fast (∼30 ns) geminate recombination is the dominating charge decay process, while nongeminate recombination has a negligible contribution. The conclusion of our work is that under solar illumination conditions geminate recombination of charges may be directly competing with efficient charge collection in polymer/fullerene solar cells. © 2007 American Chemical Society.
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| 4. |
- Infahsaeng, Yingyot, et al.
(författare)
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Transient photocurrent of bulk heterojunction solar cell characterized by ns-laser and sub-ms LED
- 2015
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Ingår i: Proceedings of SPIE. - : SPIE. - 0277-786X .- 1996-756X. ; 9659
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Konferensbidrag (refereegranskat)abstract
- We measure the transient photocurrent of APFO3:PCBM bulk heterojunction solar cells illuminated with ns-laser and sub-ms LED light sources. The ratio of the number of collective charges to the number of excited photon (external quantum efficiency, EQE) and the transient photocurrent fall times have been carried out with difference pulse durations and fluences. The EQEs characterized by ns-laser source are shown to obey the bimolecular recombination at high excitation fluences. The increasing of transient photocurrent fall times suggests that the fall times of free charge carriers are effected by deep trap density of state (DoS) and thus the free charge carriers have a sufficient time for bimolecular recombination at short circuit condition. At the same fluences, however, the EQEs characterized by sub-ms LED sources exhibit an excitation fluences independence of EQE. The transient photocurrent fall times with sub-ms LED sources are rather constant when the excitation fluences increases indicating that the deep trap DoS has less effect at short circuit condition for longer pulse duration.
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| 5. |
- Inganäs, Olle, et al.
(författare)
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Solar energy for electricity and fuels.
- 2016
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Ingår i: Ambio: a Journal of Human Environment. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 45:Suppl 1, s. 15-23
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Tidskriftsartikel (refereegranskat)abstract
- Solar energy conversion into electricity by photovoltaic modules is now a mature technology. We discuss the need for materials and device developments using conventional silicon and other materials, pointing to the need to use scalable materials and to reduce the energy payback time. Storage of solar energy can be achieved using the energy of light to produce a fuel. We discuss how this can be achieved in a direct process mimicking the photosynthetic processes, using synthetic organic, inorganic, or hybrid materials for light collection and catalysis. We also briefly discuss challenges and needs for large-scale implementation of direct solar fuel technologies.
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| 6. |
- Jespersen, Kim, et al.
(författare)
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Charge formation and transport in bulk-heterojunction solar cells based on alternating polyfluorene copolymers blended with fullerenes
- 2006
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Ingår i: Organic Electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 7:4, s. 235-242
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Tidskriftsartikel (refereegranskat)abstract
- We investigate charge formation in bulk-heterojunction solar cells based on conjugated polymers in the form of alternating polyfluorene copolymers and the methanofullerene PCBM. Using transient absorption spectroscopy we show that optimal charge formation is obtained with 20-50 wt% PCBM. This is in contrast to the maximum short circuit current density obtained at similar to 80 wt% PCBM as determined by steady state current density-voltage characterization. Hence, we show explicitly that the solar cell performance of these interpenetrating polymer networks containing PCBM is limited by charge transport rather than by formation of charges. (c) 2006 Elsevier B.V. All rights reserved.
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| 7. |
- Nemec, Hynek, et al.
(författare)
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Charge carrier dynamics in alternating polyfluorene copolymer : Fullerene blends probed by terahertz spectroscopy
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:16, s. 6558-6563
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved terahertz spectroscopy is used for investigation of photoinduced charge carrier dynamics in blends of a polyfluorene copolymer (poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl- 2',1',3-benzo-thiadiazole)]) and an electron acceptor ([6,6]-phenyl-C61-butyric acid methyl ester). The transient far-infrared response appears instantaneously after photoexcitation. We show that the transient conductivity spectrum is dominated by two major contributions: response of separated charge carriers and response of coupled polaron pairs. © 2008 American Chemical Society.
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| 8. |
- Nemec, Hynek, et al.
(författare)
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Sub-Picosecond Time-Dependent Mobility in Low-Band-Gap Polyphenylene:Fullerene Blend Probed by Terahertz Spectroscopy
- 2008
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Ingår i: Conference on Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. - : IEEE. - 1092-8081. - 9781557528599 ; , s. 3108-3109
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Konferensbidrag (refereegranskat)abstract
- Time-resolved terahertz spectroscopy is used to investigate photoinduced dynamics of charge carriers in a polymer heterojunction. We directly observe instantaneous generation of highly mobile charge carriers followed by a rapid drop in their mobility. (C) 2008 Optical Society of America
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| 9. |
- Nemec, Hynek, et al.
(författare)
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Ultrafast conductivity in a low-band-gap polyphenylene and fullerene blend studied by terahertz spectroscopy
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 79:24, s. 245326 (art no)-
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved terahertz spectroscopy and Monte Carlo simulations of charge-carrier motion are used to investigate photoinduced transient conductivity in a blend of a low-band-gap polyphenylene copolymer and fullerene derivative. The optical excitation pulse generates free holes delocalized on polymer chains. We show that these holes exhibit a very high initial mobility as their initial excess energy facilitates their transport over defects (potential barriers) on polymer chains. The conductivity then drops down rapidly within 1 ps, and we demonstrate that this decrease occurs essentially by two mechanisms. First, the carriers loose their excess energy and they thus become progressively localized between the on-chain potential barriers-this results in a mobility decay with a rate of (180 fs)(-1). Second, carriers are trapped at defects (potential wells) with a capture rate of (860 fs)(-1). At longer time scales, populations of mobile and trapped holes reach a quasiequilibrium state and further conductivity decrease becomes very slow.
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| 10. |
- Pal, S. K., et al.
(författare)
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Geminate Charge Recombination in Polymer/Fullerene Bulk Heterojunction Films and Implications for Solar Cell Function
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 132:35, s. 12440-12451
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the influence of three different fullerene derivatives on the charge generation and recombination dynamics of polymer/fullerene bulk heterojunction (BHJ) solar cell blends. Charge generation in APFO3/[70]PCBM and APFO3/[60]PCBM is very similar and somewhat slower than charge generation in APFO3/[70]BTPF. This difference qualitatively matches the trend in free energy change of electron transfer estimated from the LUMO energies of the polymer and fullerene derivatives. The first order (geminate) charge recombination rate is significantly different for the three fullerene derivatives studied and increases in the order APFO3/[70]PCBM
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