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Träfflista för sökning "WFRF:(Zhang Fengling) ;pers:(Zhang Fengling 1960)"

Sökning: WFRF:(Zhang Fengling) > Zhang Fengling 1960

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3.
  • De, Swati, et al. (författare)
  • Exciton Dynamics in Alternating Polyfluorene/Fullerene Blends
  • 2008
  • 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
  • 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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4.
  • De, Swati, et al. (författare)
  • Geminate charge recombination in alternating polyfluorene copolymer/fullerene blends
  • 2007
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 129:27, s. 8466-8472
  • 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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  • Hultmark, Sandra, 1994, et al. (författare)
  • Suppressing Co-Crystallization of Halogenated Non-Fullerene Acceptors for Thermally Stable Ternary Solar Cells
  • 2020
  • Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 30:48
  • Tidskriftsartikel (refereegranskat)abstract
    • While photovoltaic blends based on non-fullerene acceptors are touted for their thermal stability, this type of acceptor tends to crystallize, which can result in a gradual decrease in photovoltaic performance and affects the reproducibility of the devices. Two halogenated indacenodithienothiophene-based acceptors that readily co-crystallize upon mixing are studied, which indicates that the use of an acceptor mixture alone does not guarantee the formation of a disordered mixture. The addition of the donor polymer to the acceptor mixture readily suppresses the crystallization, which results in a fine-grained ternary blend with nanometer-sized domains that do not coarsen due to a high Tg ≈ 200 °C. As a result, annealing at temperatures of up to 170 °C does not markedly affect the photovoltaic performance of ternary devices, in contrast to binary devices that suffer from acceptor crystallization in the active layer. The results indicate that the ternary approach enables the use of high-temperature processing protocols, which are needed for upscaling and high-throughput fabrication of organic solar cells. Further, ternary devices display a stable photovoltaic performance at 130 °C for at least 205 h, which indicates that the use of acceptor mixtures allows to fabricate devices with excellent thermal stability.
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7.
  • Inganäs, Olle, 1951-, et al. (författare)
  • Alternating fluorene copolymer/fullerene blend solar cells
  • 2005. - 1
  • Ingår i: Organic Photovoltaics. - Boca Raton, FL, USA : CRC Press. - 082475963X - 9780824759636 ; , s. 387-402
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • Recently developed organic photovoltaics (OPVs) show distinct advantages over their inorganic counterparts due to their lighter weight, flexible shape, versatile materials synthesis and device fabrication schemes, and low cost in large-scale industrial production. Although many books currently exist on general concepts of PV and inorganic PV materials and devices, few are available that offer a comprehensive overview of recently fast developing organic and polymeric PV materials and devices.Organic Photovoltaics: Mechanisms, Materials, and Devicesfills this gap. The book provides an international perspective on the latest research in this rapidly expanding field with contributions from top experts around the world.  It presents a unified approach comprising three sections: General Overviews; Mechanisms and Modeling; and Materials and Devices. Discussions include sunlight capture, exciton diffusion and dissociation, interface properties, charge recombination and migration, and a variety of currently developing OPV materials/devices. The book also includes two forewords: one by Nobel Laureate Dr. Alan J. Heeger, and the other by Drs. Aloysius Hepp and Sheila Bailey of NASA Glenn Research Center.Organic Photovoltaics equips students, researchers, and engineers with knowledge of the mechanisms, materials, devices, and applications of OPVs necessary to develop cheaper, lighter, and cleaner renewable energy throughout the coming decades.
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8.
  • Jespersen, Kim, et al. (författare)
  • Charge formation and transport in bulk-heterojunction solar cells based on alternating polyfluorene copolymers blended with fullerenes
  • 2006
  • Ingår i: Organic Electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 7:4, s. 235-242
  • 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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9.
  • Jiang, Qinglin, et al. (författare)
  • High Thermoelectric Performance in n-Type Perylene Bisimide Induced by the Soret Effect
  • 2020
  • Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 32:45
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-cost, non-toxic, abundant organic thermoelectric materials are currently under investigation for use as potential alternatives for the production of electricity from waste heat. While organic conductors reach electrical conductivities as high as their inorganic counterparts, they suffer from an overall low thermoelectric figure of merit (ZT) due to their small Seebeck coefficient. Moreover, the lack of efficient n-type organic materials still represents a major challenge when trying to fabricate efficient organic thermoelectric modules. Here, a novel strategy is proposed both to increase the Seebeck coefficient and achieve the highest thermoelectric efficiency for n-type organic thermoelectrics to date. An organic mixed ion-electron n-type conductor based on highly crystalline and reduced perylene bisimide is developed. Quasi-frozen ionic carriers yield a large ionic Seebeck coefficient of -3021 mu V K-1, while the electronic carriers dominate the electrical conductivity which is as high as 0.18 S cm(-1)at 60% relative humidity. The overall power factor is remarkably high (165 mu W m(-1)K(-2)), with aZT= 0.23 at room temperature. The resulting single leg thermoelectric generators display a high quasi-constant power output. This work paves the way for the design and development of efficient organic thermoelectrics by the rational control of the mobility of the electronic and ionic carriers.
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10.
  • Jin, Yingzhi, 1991- (författare)
  • Organic electronic devices for solar energy conversion and storage
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis focuses on two types of organic electronic devices: organic photovoltaic (OPV) devices for solar energy conversion, and photo-capacitors for energy storage.OPVs have been under the focus of research for decades as an effective technique to convert solar energy to electricity. So far, the efficiency of bulk heterojunction OPV consisting donor and acceptor materials is approaching to 18% with non-fullerene acceptor (NFA), which make it close to commercialization. The process of charge generation and recombination are two competing processes in OPVs, since their requirements for the active layer morphology are contradictory. Large donor/acceptor interfaces facilitate charge generation but hinder the transporting pathways for charge transportation. The simultaneously enhanced charge generation and transportation are achieved by using the ternary strategy in my first paper. The fully mixed donors and NFAs are beneficial for the charge generation and fullerene is introduced as an extra electron transport channel. The hierarchical morphology of the blend film is confirmed by the TEM results. The voltage loss analyses indicate that the hierarchical morphology could suppress unfavorable charge transfer state and non-radiative recombination loss. In my second paper, efficient charge generation with low voltage loss are achieved in the solar cells by rational designing a series of NFAs. The detailed voltage losses are discussed in these binary systems, revealing the critical relationship between radiative efficiency and device performance.To harvest photocurrent in OPVs, long lifetime triplet excitons are highly expected to be good candidates. The potential of triplet materials in OPVs has been explored since 1970s. However, the performance of the triplet materials-based OPVs is far behind. The voltage loss in triplet OPVs is intensively studied in my third work. A higher open circuit voltage (0.88 V) is observed for Ir(FOtbpa)3-based devices than those of Ir(Ftbpa)3 (0.80 V) despite a lower charge transfer state energy. To understand above result, the voltage losses through radiative and non-radiative recombination pathways in two devices are quantitively investigated, which indicate a reduced non-radiative recombination loss in the Ir(FOtbpa)3-based devices.The fluctuation of sun irradiation resulting the unstable output power of solar cells. Therefore, it is important to store electricity of solar cells for later use. Integrated photo-capacitor (IPC), combining a solar cell and a super-capacitor by sharing one common electrode, is able to simultaneously realize the energy harvesting and storage. Building upon this advantage, IPC devices received tremendous research attention. In my fourth and last papers, we introduced super-capacitors to construct IPC devices with OPV device or modules. A free standing thick- PEDOT:PSS film is successfully integrated into an all solution-processed IPC device as the common electrode. Resulting devices demonstrate good performance and outstanding stability. With solar PV modules, a higher voltage can be generated and stored by asymmetric supercapacitors, which could be used as a portable power unit.
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