EDOT-diketopyrrolopyrrole copolymers for polymer solar cells

Titelangaben

Wang, Chao ; Müller, Christian J. ; Gann, Eliot ; Liu, Amelia C. Y. ; Thelakkat, Mukundan ; McNeill, Christopher R.:
EDOT-diketopyrrolopyrrole copolymers for polymer solar cells.
In: Journal of Materials Chemistry A. Bd. 4 (2016) Heft 9 . - S. 3477-3486.
ISSN 2050-7496
DOI: https://doi.org/10.1039/C5TA10078J

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Abstract

The photovoltaic properties of a series of diketopyrrolo3{,}4-cpyrrole (DPP) copolymers containing 3{,}4-ethylenedioxythiophene (EDOT) as a comonomer are reported. With use of different aryl flanking units on the DPP core{,} namely thiophene{,} pyridine or phenyl{,} optical gaps ranging from 1.91 eV to 1.13 eV are achieved. When blended with the fullerene derivative 6{,}6-phenyl C71-butyric acid methyl ester (PC71BM){,} the thiophene-flanked copolymer PDPPT2-EDOT with an optical gap of 1.13 eV was found to have the best photovoltaic performance{,} with an efficiency of 2.5% in an inverted device architecture. Despite having the lowest open circuit voltage of the three polymers studied{,} PDPPT2-EDOT-based devices were able to achieve superior efficiencies due to the high short circuit current of up to similar15 mA cm-2. PDPPT2-EDOT-based devices also exhibit higher external quantum efficiencies which are associated with a superior microstructure - as revealed by transmission electron microscopy (TEM) and grazing incidence wide-angle X-ray scattering (GIWAXS) - which is associated with the enhanced aggregation tendency of PDPPT2-EDOT chains. In particular PDPPT2-EDOT : PC71BM blends were found to have a finer phase separated morphology with superior thin-film crystallinity. Surface morphology was also investigated with atomic force microscopy and near-edge X-ray absorption fine-structure spectroscopy.