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Correlating Structure with Function in Thermally Annealed PCDTBT:PC70BM Photovoltaic Blends

DOI: 10.1002/adfm.201102510 DOI Help

Authors: Tao Wang (University of Sheffield) , Andrew Pearson (University of Sheffield) , Alan Dunbar (University of Sheffield) , Paul Staniec (Diamond Light Source) , Darren Watters (University of Sheffield) , Hunan Yi (University of Sheffield, U.K.) , Anthony J. Ryan (University of Sheffield, U.K.) , Richard A. L. Jones (University of Sheffield, U.K.) , Ahmed Iraqi (University of Sheffield, U.K.) , David Lidzey (University of Sheffield)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Advanced Functional Materials , VOL 22 (7) , PAGES 1399-1408

State: Published (Approved)
Published: April 2012
Diamond Proposal Number(s): 1203

Abstract: A range of optical probes are used to study the nanoscale-structure and electronic-functionality of a photovoltaic-applicable blend of the carbazole co-polymer poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3 '-benzothiadiazole) (PCDTBT) and the electronic accepting fullerene derivative (6,6)-phenyl C70-butyric acid methyl ester (PC70BM). In particular, it is shown that the glass transition temperature of a PCDTBT:PC70BM blend thin-film is not sensitive to the relative blend-ratio or film thickness (at 1:4 blending ratio), but is sensitive to casting solvent and the type of substrate on which it is deposited. It is found that the glass transition temperature of the blend reduces on annealing; an observation consistent with disruption of pp stacking between PCDTBT molecules. Reduced pp stacking is correlated with reduced hole-mobility in thermally annealed films. It is suggested that this explains the failure of such annealing protocols to substantially improve device-efficiency. The annealing studies demonstrate that the blend only undergoes coarse phase-separation when annealed at or above 155 degrees C, suggesting a promising degree of morphological stability of PCDTBT:PC70BM blends.

Journal Keywords: Pcdtbt; Pc[70]Bm; Bulk-Heterojunction; Organic Photovoltaics; Solar Cells

Subject Areas: Chemistry, Physics

Instruments: I19-Small Molecule Single Crystal Diffraction

Added On: 08/10/2012 14:25

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