Browsing by Author "Tao, C"

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    Controlling hierarchy in solution-processed polymer solar cells based on crosslinked P3HT
    (Wiley-VCH Verlag GmbH & Co. KGaA, 2013-01-01) Tao, C; Aljada, M; Shaw, PE; Lee, KH; Cavaye, H; Balfour, MN; Borthwick, RJ; James, M; Burn, PL; Gentle, IR; Meredith, P
    Understanding and controlling the morphology of donor/acceptor blends is critical for the development of solution processable organic solar cells. By crosslinking a poly(3-n-hexylthiophene-2,5-diyl) (P3HT) film we have been able to spin-coat [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) onto the film to form a structure that is close to a bilayer, thus creating an ideal platform for investigating interdiffusion in this model system. Neutron reflectometry (NR) demonstrates that without any thermal treatment a smaller amount of PCBM percolates throughout the crosslinked P3HT when compared to a non-crosslinked P3HT film. Using time-resolved NR we also show thermal annealing increases the rate of diffusion, resulting in a near-uniform distribution of PCBM throughout the polymer film. XPS measurements confirm the presence of both P3HT and PCBM at the annealed film's surface indicating that the two components are intermixed. Photovoltaic devices fabricated using this bilayer approach and suitable annealing conditions yielded comparable power conversion efficiencies to bulk heterojunction devices made from the same materials. The crosslinking procedure has also enabled the formation of patterned P3HT films by photolithography. Pillars with feature sizes down to 2 μm were produced and after subsequent deposition of PCBM and thermal annealing devices with efficiencies of up to 1.4% were produced.© 2013, Wiley-VCH Verlag GmbH & Co. KGaA
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    Determination of fullerene scattering length density: a critical parameter for understanding the fullerene distribution in bulk heterojunction organic photovoltaic devices
    (American Chemical Society, 2014-01-27) Clulow, AJ; Armin, A; Lee, KH; Pandey, AK; Tao, C; Velusamy, M; James, M; Nelson, A; Burn, PL; Gentle, IR; Meredith, P
    Fullerene derivatives are commonly used as electron acceptors in combination with (macro)molecular electron donors in bulk heterojunction (BHJ) organic photovoltaic (OPV) devices. Understanding the BHJ structure at different electron donor/acceptor ratios is critical to the continued improvement and development of OPVs. The high neutron scattering length densities (SLDs) of the fullerenes provide effective contrast for probing the distribution of the fullerene within the blend in a nondestructive way. However, recent neutron scattering studies on BHJ films have reported a wide range of SLDs ((3.6–4.4) × 10–6 Å–2) for the fullerenes 60-PCBM and 70-PCBM, leading to differing interpretations of their distribution in thin films. In this article, we describe an approach for determining more precisely the scattering length densities of the fullerenes within a polymer matrix in order to accurately quantify their distribution within the active layers of OPV devices by neutron scattering techniques.© 2014, American Chemical Society.
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    Time-resolved neutron reflectometry and photovoltaic device studies on sequentially deposited PCDTBT-fullerenel layers
    (ACS Publications, 2014-09) Clulow, AJ; Tao, C; Lee, KH; Velusamy, M; McEwan, JA; Shaw, PE; Yamada, NL; James, M; Burn, PL; Gentle, IR; Meredith, P
    We have used steady-state and time-resolved neutron reflectometry to study the diffusion of fullerene derivatives into the narrow optical gap polymer poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) to explore the sequential processing of the donor and acceptor for the preparation of efficient organic solar cells. It was found that when [6,6]-phenyl-C61-butyric-acid-methyl-ester (60-PCBM) was deposited onto a thin film of PCDTBT from dichloromethane (DCM), a three-layer structure was formed that was stable below the glass-transition temperature of the polymer. When good solvents for the polymer were used in conjunction with DCM, both 60-PCBM and [6,6]-phenyl-C71-butyric-acid-methyl-ester (70-PCBM) were seen to form films that had a thick fullerene layer containing little polymer and a PCDTBT-rich layer near the interface with the substrate. Devices composed of films prepared by sequential deposition of the polymer and fullerene had efficiencies of up to 5.3%, with those based on 60-PCBM close to optimized bulk heterojunction (BHJ) cells processed in the conventional manner. Sequential deposition of pure components to form the active layer is attractive for large-area device fabrication, and the results demonstrate that this processing method can give efficient solar cells. © 2014, American Chemical Society.