| 1. |
- Liu, Yanfeng, et al.
(författare)
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In Situ Optical Studies on Morphology Formation in Organic Photovoltaic Blends
- 2021
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Ingår i: Small Methods. - : John Wiley & Sons. - 2366-9608. ; 5:10, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of bulk heterojunction (BHJ) based organic solar cells is highly dependent on the morphology of the blend film, which is a result of a fine interplay between donor, acceptor, and solvent during the film drying. In this work, a versatile set-up of in situ spectroscopies is used to follow the morphology evolution during blade coating of three iconic BHJ systems, including polymer:fullerene, polymer:nonfullerene small molecule, and polymer:polymer. the drying and photoluminescence quenching dynamics are systematically study during the film formation of both pristine and BHJ films, which indicate that the component with higher molecular weight dominates the blend film formation and the final morphology. Furthermore, Time-resolved photoluminescence, which is employed for the first time as an in situ method for such drying studies, allows to quantitatively determine the extent of dynamic and static quenching, as well as the relative change of quantum yield during film formation. This work contributes to a fundamental understanding of microstructure formation during the processing of different blend films. The presented setup is considered to be an important tool for the future development of blend inks for solution-cast organic or hybrid electronics.
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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. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- Shao, Shuyan, et al.
(författare)
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Enhanced Performance of Inverted Polymer Solar Cells by Using Poly(ethylene oxide)-Modified ZnO as an Electron Transport Layer
- 2013
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society. - 1944-8244 .- 1944-8252. ; 5:2, s. 380-385
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report enhanced performance of inverted polymer solar cells composed of poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1):[6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) blends by using poly(ethylene oxide) (PEO)-modified ZnO as an electron transport layer. It is found that PEO modification to the ZnO nanoparticle surface can effectively passivate the surface traps of ZnO, suppress the recombination loss of carriers, reduce the series resistance, and improve the electrical coupling of ZnO/active layer. Consequently, both the short-circuit current (J(SC)) and the fill factor (FF) of the inverted solar cells are considerably improved. The resulting power conversion efficiency (PCE) is improved to 5.64% as compared to 4.5% of the reference device using a ZnO electron transport layer. Moreover, this approach can also successfully improve the J(SC) and FF of anther inverted solar cell composed of poly[N-9 -hepta-decanyl-2,7-carbazole-alt-5,5-(4,7-dithienyl-2,1,3-benzothiadiazole)] (PCDTBT):PC71BM blends. The PCE of the device based on the PEO-modified ZnO layer is increased to 6.59% from 5.39% of the reference device based on the ZnO layer.
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| 10. |
- Shao, Shuyan, et al.
(författare)
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Optimizing ZnO nanoparticle surface for bulk heterojunction hybrid solar cells
- 2013
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 118, s. 43-47
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Tidskriftsartikel (refereegranskat)abstract
- The performance of hybrid solar cells composed of polymer and ZnO is mainly hindered by the defects of ZnO. Here, we investigate the effects of ZnO nanoparticle surface modification with poly(ethylene oxide) (PEO) on the performance of bulk heterojunction hybrid solar cells based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and ZnO nanoparticles. The reference device using ZnO nanoparticles as electron acceptor shows an open-circuit voltage (VOC) of 0.83 V, a short-circuit current (JSC) of 3.00 mA/cm2, a fill factor (FF) of 0.46 and a power conversion efficiency (PCE) of 1.15%. After modification with very small amount of PEO, the PCE will be enhanced, which is attributed to less surface traps of ZnO nanoparticles with PEO modification. With optimized PEO (0.05%) modified ZnO nanoparticles as electron acceptors, the device typically shows a VOC of 0.86 V, a JSC of 3.84 mA/cm2, a FF of 0.51 and a PCE of 1.68% due to less recombination loss of carriers, smaller series resistance, and improved electrical coupling between ZnO nanoparticle and MEH-PPV. However, further increase of PEO content to 0.3% will deteriorate device performance.
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