SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Tvingstedt Kristofer) ;pers:(Vandewal Koen)"

Sökning: WFRF:(Tvingstedt Kristofer) > Vandewal Koen

  • Resultat 1-10 av 12
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Gadisa, Abay, et al. (författare)
  • Bipolar Charge Transport in Fullerene Molecules in a Bilayer and Blend of Polyfluorene Copolymer and Fullerene
  • 2010
  • Ingår i: ADVANCED MATERIALS. - : Wiley. - 0935-9648. ; 22:9, s. 1008-
  • Tidskriftsartikel (refereegranskat)abstract
    • Efficient polymer solar cells typically contain the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which promotes dissociation of excited states and enhances charge transport. The ability of PCBM to transport holes in solar cell bulk heterojunction films is monitored via the electroluminescence emission of a bulk heterojunction blend of PCBM and a polyfluorene copolymer. In polymer/fullerene bilayer diodes, fullerene emission is also observed.
  •  
2.
  • Müller, Christian, et al. (författare)
  • Phase behaviour of liquid-crystalline polymer/fullerene organic photovoltaic blends : thermal stability and miscibility
  • 2011
  • Ingår i: Journal of Materials Chemistry. - : RSC Publishing. - 0959-9428 .- 1364-5501. ; 21, s. 10676-10684
  • Tidskriftsartikel (refereegranskat)abstract
    • The thermal behaviour of an organic photovoltaic (OPV) binary system comprised of a liquidcrystalline fluorene-based polymer and a fullerene derivative is investigated. We employ variabletemperature 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.
  •  
3.
  • Tang, Zheng, et al. (författare)
  • Interlayer for Modified Cathode in Highly Efficient Inverted ITO-Free Organic Solar Cells
  • 2012
  • Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:4, s. 554-
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
4.
  • Tang, Zheng, et al. (författare)
  • Semi-Transparent Tandem Organic Solar Cells with 90% Internal Quantum Efficiency
  • 2012
  • Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 2:12, s. 1467-1476
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
5.
  • Tvingstedt, Kristofer, et al. (författare)
  • Electroluminescence from Charge Transfer States in Polymer Solar Cells
  • 2009
  • Ingår i: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:33, s. 11819-11824
  • Tidskriftsartikel (refereegranskat)abstract
    • In this article we report the weak but omnipresent electroluminescence (EL) from several types of organic polymer:fullerene bulk heterojunction solar cells biased in the forward direction. The light emitted from blends of Some commonly used polymers and the fullerene molecule is significantly different from that of any of the pure materials comprising the blend. The lower energy of the blend EL is found to correlate with both the voltage onset of emission and the open-circuit voltage of the photovoltaic cell under solar illumination. WE., accordingly interpret the emission to originate from interfacial charge transfer state recombination and emphasize EL as a very valuable tool to characterize the charge transfer state present in donor/acceptor organic photovoltaic (OPV) cells.
  •  
6.
  • Tvingstedt, Kristofer, et al. (författare)
  • On the Dissociation Efficiency of Charge Transfer Excitons and Frenkel Excitons in Organic Solar Cells: A Luminescence Quenching Study
  • 2010
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 114:49, s. 21824-21832
  • Tidskriftsartikel (refereegranskat)abstract
    • The field dependence of photocurrent found in many organic solar cells is a significant and detrimental setback for internal quantum efficiency. In this work we study the important contribution to this field dependence due to the dissociation efficiency of the weakly bound interfacial charge transfer (CT) state, crucial for organic bulk heterojunction solar cells. Three different donor polymers and two different acceptors are examined, and their respective dissociation characteristics are evaluated by photoluminescence (PL) quenching, both for Frenkel excitons and for the intermolecular charge transfer excitons. We observe that while the field-dependent photocurrent for pure polymers does correlate well with quenching efficiency, the CT exciton quenching from the blend generally displays a less pronounced correlation with extracted photocurrent. We further note that while the electroluminescence and photoluminescence of the pure polymer are identical, we observe a red shift for the blend electroluminescence. This indicates that lower energetic states, not visible in PL, are available in the blend. The emissive state of the blends probed by PL is therefore proposed to originate from sites that are involved in photocurrent generation to a lesser extent.
  •  
7.
  • Vandewal, Koen, et al. (författare)
  • Charge-Transfer States and Upper Limit of the Open-Circuit Voltage in Polymer: Fullerene Organic Solar Cells
  • 2010
  • Ingår i: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS. - : Institute of Electrical and Electronics Engineers (IEEE). - 1077-260X. ; 16:6, s. 1676-1684
  • Tidskriftsartikel (refereegranskat)abstract
    • The power conversion efficiency of polymer: fullerene bulk heterojunction solar cells depends on the generated photocurrent and photovoltage. Here we show, using the thermodynamic theory of detailed balance, that the photovoltage in particular is limited by the presence of polymer: fullerene material interaction, resulting in the formation of a weak donor-acceptor charge transfer complex (CTC). Excited CTCs, or charge transfer (CT) states, are visible in highly sensitive measurements of the absorption and photovoltaic action spectrum, or in photoluminescence and electroluminescence measurements. It is shown that photovoltaic and electroluminescent actions of the polymer: fullerene CTC are related by a reciprocity relation. This relation reproduces the measured open-circuit voltage (V-oc) of the photovoltaic device under solar conditions. Also, the temperature and illumination intensity dependence of V-oc is reproduced by the theory. Assuming perfect conditions for charge generation and recombination, a maximum obtainable V-oc value in function of polymer: fullerene CTC properties is derived.
  •  
8.
  • Vandewal, Koen, et al. (författare)
  • Charge Transfer States in Organic Donor-Acceptor Solar Cells
  • 2011
  • Ingår i: Semiconductors and semimetals. - : Academic Press. - 0080-8784. ; 85, s. 261-295
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
9.
  • Vandewal, Koen, et al. (författare)
  • On the origin of the open-circuit voltage of polymer-fullerene solar cells
  • 2009
  • Ingår i: NATURE MATERIALS. - : Springer Science and Business Media LLC. - 1476-1122 .- 1476-4660. ; 8:11, s. 904-909
  • Tidskriftsartikel (refereegranskat)abstract
    • The increasing amount of research on solution-processable, organic donor-acceptor bulk heterojunction photovoltaic systems, based on blends of conjugated polymers and fullerenes has resulted in devices with an overall power-conversion efficiency of 6%. For the best devices, absorbed photon-to-electron quantum efficiencies approaching 100% have been shown. Besides the produced current, the overall efficiency depends critically on the generated photovoltage. Therefore, understanding and optimization of the open-circuit voltage (V-oc) of organic solar cells is of high importance. Here, we demonstrate that charge-transfer absorption and emission are shown to be related to each other and V-oc in accordance with the assumptions of the detailed balance and quasi-equilibrium theory. We underline the importance of the weak ground-state interaction between the polymer and the fullerene and we confirm that V-oc is determined by the formation of these states. Our work further suggests alternative pathways to improve V-oc of donor-acceptor devices.
  •  
10.
  • Vandewal, Koen, et al. (författare)
  • Polarization anisotropy of charge transfer absorption and emission of aligned polymer: fullerene blend films
  • 2012
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 86:3, s. 035212-
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-10 av 12

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy