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Sökning: WFRF:(Zhang Fengling) > (2011)

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1.
  • Andersson, Mattias, et al. (författare)
  • Mobility and fill factor correlation in geminate recombination limited solar cells
  • 2011
  • Ingår i: Journal of Applied Physics. - American Institute of Physics (AIP). - 0021-8979. ; 110:2, s. 024509
  • Tidskriftsartikel (refereegranskat)abstract
    • Empirical data for the fill factor as a function of charge carrier mobility for two different polymer: fullerene systems is presented and analyzed. The results indicate that charge extraction depth limitations and space charge effects are inconsistent with the observed behavior, and the decrease in the fill factor is, instead, attributed to the field-dependent charge separation and geminate recombination. A solar cell photocurrent limited by the Onsager-Braun charge transfer exciton dissociation is shown to be able to accommodate the experimental observations. Charge dissociation limited solar cells always benefit from increased mobilities, and the negative contribution from the reduced charge separation is shown to be much more important for the fill factor in these material systems than any adverse effects from charge carrier extraction depth limitations or space charge effects due to unbalanced mobilities. The logarithmic dependence of the fill factor on the mobility for such a process is also shown to imply that simply increasing the mobilities is an impractical way to reach very high fill factors under these conditions since unrealistically high mobilities are required. A more controlled morphology is, instead, argued to be necessary for high performance.
2.
  • Du, Chun, et al. (författare)
  • 9-Alkylidene-9H-Fluorene-Containing Polymer for High-Efficiency Polymer Solar Cells
  • 2011
  • Ingår i: Macromolecules. - American Chemical Society. - 0024-9297. ; 44:19, s. 7617-7624
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel donor-acceptor copolymer containing 9-alkylidene-9H-fluorene unit in the main chain, poly[9-(1-hexylheptylidene)-2,7-fluorene-alt-5, 5-(4,7-di-2-thienyl-5,6-dialkoxy-2,1,3-benzothiadiazole)] (PAFDTBT), has been synthesized and evaluated in bulk heterojunction polymer solar cells (BHJ PSCs). The polymer possesses a low band gap of 1.84 eV, a low-lying HOMO energy level (5.32 eV), and excellent solubility in common organic solvents. PSCs based on PAFDTBT and (6,6)-phenyl-C(71)-butyric add methyl ester (PC(71)BM) demonstrate a power conversion efficiency (PCE) of 6.2% with a high fill factor (FF) of 0.70, which indicates that 9-alkylidene-9H-fluorene can be a very useful building block for constructing narrow band gap conjugated polymers for high-efficiency BHJ PSCs.
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3.
  • Li, Weiwei, et al. (författare)
  • The Effect of additive on performance and shelf-stability of HSX-1/PCBM photovoltaic devices
  • 2011
  • Ingår i: Organic electronics. - Elsevier Science B.V., Amsterdam.. - 1566-1199. ; 12:9, s. 1544-1551
  • Tidskriftsartikel (refereegranskat)abstract
    • How 1,8-diiodooctane (DIO) enhances performance of polymer solar cells based on polymer HXS-1 and fullerene [6,6]-phenyl C(71)-butyric acid methyl ester (PC(71)BM) from 3.6% to 5.4% is scrutinized with several techniques by comparing devices or blend films spin-coated from dichlorobenzene (DCB) to those from DCB/DIO (97.5:2.5 v/v). Morphology of blend films is examined with atomic force microscopy (AFM), transmission electron microscopy (TEM) and electron tomography (3-D TEM), respectively. Charge generation and recombination is studied with photoluminescence, and charge transport with field effect transistors. The morphology with domain size in 10-20 nm and vertical elongated clusters formed in DIO system is supposed to facilitate charge transport and minimize charge carrier recombination, which are the main reasons for enhancing power conversion efficiency (PCE) from 3.6% (without DIO) to 5.4% (with DIO). Furthermore, a two year inspection shows no significant impact of DIO on the shelf-stability of the solar cells. No visible degradation in the second year indicates that the morphology of the active layers in the devices is relatively stable after initial relaxation in the first year.
4.
  • Ma, Zaifei, et al. (författare)
  • Enhance performance of organic solar cells based on an isoindigo-based copolymer by balancing absorption and miscibility of electron acceptor
  • 2011
  • Ingår i: Applied Physics Letters. - American Institute of Physics (AIP). - 0003-6951. ; 99:14, s. 143302
  • Tidskriftsartikel (refereegranskat)abstract
    • Superior absorption of PC(71)BM in visible region to that of PC(61)BM makes PC(71)BM a predominant acceptor for most high efficient polymer solar cells (PSCs). However, we will demonstrate that power conversion efficiencies (PCEs) of PSCs based on poly[N,N-bis(2-hexyldecyl)isoindigo-6, 6-diyl-alt-thiophene-2,5-diyl] (PTI-1) with PC(61)BM as acceptor are 50% higher than their PC71BM counterparts under illumination of AM1.5G. AFM images reveal different topographies of the blends between PTI-1:PC(61)BM and PTI-1:PC(71)BM, which suggests that acceptors miscibility plays a more important role than absorption. The photocurrent of 9.1 mA/cm(2) is among the highest value in PSCs with a driving force for exciton dissociation less than 0.2 eV.
5.
  • O Reese, Matthew, et al. (författare)
  • Consensus stability testing protocols for organic photovoltaic materials and devices
  • 2011
  • Ingår i: SOLAR ENERGY MATERIALS AND SOLAR CELLS. - Elsevier Science B.V., Amsterdam.. - 0927-0248. ; 95:5, s. 1253-1267
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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6.
  • Wang, Yaling, et al. (författare)
  • Enhanced performance and stability in polymer photovoltaic cells using lithium benzoate as cathode interfacial layer
  • 2011
  • Ingår i: SOLAR ENERGY MATERIALS AND SOLAR CELLS. - Elsevier Science B.V., Amsterdam.. - 0927-0248. ; 95:4, s. 1243-1247
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the enhanced performance and stability of polymer solar cells based on regioregular poly(3-hexylthiophene)(P3HT) and methanofullerene [6,6]-phenyl C-61-butyric acid methyl ester (PCBM) blend using lithium benzoate (C6H5COOLi) as cathode buffer layer between the active layer and the Al cathode. The effects of the C6H5COOLi thickness on the performance of polymer solar cell are also investigated. Under 100 mW/cm(2) white light illumination, the device with 1 nm thick C6H5COOLi as cathode buffer layer exhibits power conversion efficiency (PCE) as high as 3.41 +/- 0.07% and the device stability is greatly extended. Compared to the solar cell with LiF/AI cathode, the PCE is increased ca. 9.4%. Introduction of C6H5COOLi buffer layer effectively increases the shunt resistance and improves the photo-generated charge collection. The improved performance may attribute to the dissociation of semi-conducting C6H5COOLi upon deposition to liberate Li with a low work function, which reduces the interface resistance of the active layer and the cathode and enhances the interior electric field that may result in efficient charge transportion. In addition, the C6H5COOLi layer may serve as an effective oxygen and moisture diffusion barrier for the organic solar cells. Therefore. C6H5COOLi is a promising candidate as an interlayer to improve the efficiency of electron collection and to reduce the ambience influence on the stability of polymer solar cells.
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7.
  • Wang, Zhongqiang, et al. (författare)
  • Mixed solvents for reproducible photovoltaic bulk heterojunctions
  • 2011
  • Ingår i: Journal of Photonics for Energy. - Society of Photo-optical Instrumentation Engineers (SPIE). - 1947-7988. ; 1:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Most efficient polymer solar cells are usually fabricated from toxic organic solvents, such as chloroform, chlorobenzene, or dichlorobenzene (ODCB). Here, we demonstrate a power conversion efficiency of 4.5% in solar cells with a new blue polymer poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt- thiophene-2,5-diyl] (TQ1) mixed with PC71BM and processed from mixed solvents of toluene and ODCB in a ratio of 9:1. Decreasing the content of ODCB makes device processing more compatible with the environment for large scale production, with 10% reduction of photocurrent compared to devices from pure ODCB under optimized conditions. In addition, less variation of photocurrent is obtained in solar cells processed from mixed solvents than from pure ODCB due to varying nanostructure in the blends, which is also critical for production. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).
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