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Shoaee S.,Center for Plastic Electronics | Durrant J.R.,Center for Plastic Electronics
Journal of Materials Chemistry C | Year: 2015

Transient absorption spectroscopy is commonly used to probe the yield and kinetics of excited states of materials. We present a transient absorption spectroscopic assay of oxygen diffusion in a series of solution-processed polymer films. The films were partially encapsulated with an epoxy/glass top barrier as a simple model system for organic photovoltaic and light emitting devices with metal top contacts. The results presented herein show that this spectroscopic approach can be a versatile and quantitative in situ assay of local oxygen concentrations in such organic semiconductor films. With our current apparatus, the approach has a time resolution of 5 seconds, thereby enabling direct measurement of oxygen diffusion kinetics into a semiconductor film. The versatility of this approach suggests it could be widely applicable to measurement of oxygen diffusion into organic optoelectronic devices, including for example oxygen diffusion through encapsulation and barrier layers. Employing this approach, we demonstrate significant differences in oxygen diffusion kinetics between different semiconducting polymers. We furthermore demonstrate the impact of an additional getter (ZnO) and light exposure upon the local oxygen concentration, providing new insights into the role of oxygen diffusion kinetics in determining the environmental stability of organic semiconductors. © The Royal Society of Chemistry.

Dalgleish S.,University of Edinburgh | Labram J.G.,Center for Plastic Electronics | Li Z.,University of Cambridge | Wang J.,University of Cambridge | And 4 more authors.
Journal of Materials Chemistry | Year: 2011

The synthesis and full characterisation of a novel indole-substituted nickel dithiolene [Ni(mi-5edt)2] (3) is reported, and compared to its alkyl-substituted analogue [Ni(mi-5hdt)2] (4) that has been previously communicated [Dalgleish et al., Chem. Commun., 2009, 5826] [mi-5edt = 1-(N-methylindol-5-yl)-ethene-1,2-dithiolate; mi-5hdt = 1-(N-methylindol-5-yl)- hex-1-ene-1,2-dithiolate)]. Both complexes are shown to undergo oxidative electropolymerisation, yielding polymer films that retain the redox and optical properties of the monomer. The more soluble analogue 4 is shown to form high quality thin films by spin coating, which have been utilised to fabricate field-effect transistors (FETs) and bulk heterojunction photovoltaic devices (BHJ-PVs). From FET studies, the material shows ambipolar charge transport behaviour, with a maximum carrier mobility of ∼10-6 cm 2 V-1 s-1 for electrons. By using 4 simultaneously as the electron acceptor as well as a NIR sensitiser in BHJ-PVs, the complex is shown to contribute to the photocurrent, extending light harvesting into the NIR region. © 2011 The Royal Society of Chemistry.

Fei Z.,Imperial College London | Ashraf R.S.,Imperial College London | Huang Z.,Imperial College London | Smith J.,Center for Plastic Electronics | And 6 more authors.
Chemical Communications | Year: 2012

We report the first synthesis of a fused germaindacenodithiophene monomer and its polymerisation with 2,1,3-benzothiadiazole by Suzuki polycondensation. The resulting polymer, PGeTPTBT, is semicrystalline, despite the presence of four bulky 2-ethylhexyl groups. Blends with P 70CBM afford solar cells with efficiencies of 5.02%. © 2012 The Royal Society of Chemistry.

Voigt M.M.,Center for Plastic Electronics | MacKenzie R.C.I.,Center for Plastic Electronics | MacKenzie R.C.I.,Albert Ludwigs University of Freiburg | King S.P.,Center for Plastic Electronics | And 10 more authors.
Solar Energy Materials and Solar Cells | Year: 2012

We investigate the relationship between processing parameters and the device performance of gravure printed organic solar cells. Ink viscosity, surface energy and surface roughness are studied to optimise the printing process. Surfactants, additives and surface modification by plasma cleaning are utilised to achieve homogeneous printing of multilayer OPV device architectures. It is found that use of high boiling point solvents with high solubilities leads to a desirable surface morphology. The use of a printed metal oxide electrode within the inverted structure leads to devices with lifetimes exceeding those of devices in standard structures without the need for encapsulation. © 2012 Elsevier B.V.

Zhang X.,U.S. National Institute of Standards and Technology | Richter L.J.,U.S. National Institute of Standards and Technology | Delongchamp D.M.,U.S. National Institute of Standards and Technology | Kline R.J.,U.S. National Institute of Standards and Technology | And 10 more authors.
Journal of the American Chemical Society | Year: 2011

We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm 2 V -1 s -1, with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases. Thermal annealing generally reduces both the face-on population and the misoriented edge-on domains. The highest hole mobilities of this series were obtained from edge-on molecular packing and in-plane liquid-crystalline texture, but films with a bimodal orientation distribution and no discernible in-plane texture exhibited surprisingly comparable mobilities. The high hole mobility may therefore arise from the molecular packing feature common to the entire polymer series: backbones that are strictly oriented parallel to the substrate plane and coplanar with other backbones in the same layer. © 2011 American Chemical Society.

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