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Open AccessArticle

The Influence of Alkoxy Substitutions on the Properties of Diketopyrrolopyrrole-Phenyl Copolymers for Solar Cells

1
Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
2
Organic Electronics, PV/PMEPV/OPV, IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium
3
Université Libre de Bruxelles, Laboratoire de Chimie des Polymères, CP 206/1, Boulevard du Triomphe, B-1050 Brussels, Belgium
*
Author to whom correspondence should be addressed.
§
These authors contributed equally to this manuscript.
Materials 2013, 6(7), 3022-3034; https://doi.org/10.3390/ma6073022
Received: 20 May 2013 / Revised: 2 July 2013 / Accepted: 9 July 2013 / Published: 22 July 2013
(This article belongs to the Section Energy Materials)
A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties correlated with an increase in chain flexibility. Well-defined oligomers were synthesized to verify the observed structure-property relationship. Surprisingly, methoxy substitution on the benzene spacer resulted in higher melting and crystallization temperatures in the synthesized oligomers. This trend is not observed in the polymers, where the improved interactions are most likely counteracted by the larger conformational possibilities in the polymer chain upon alkoxy substitution. The best photovoltaic performance was obtained for the parent polymer: fullerene blends whereas the modifications on the other two polymers result in reduced open-circuit voltage and varying current densities under similar processing conditions. The current densities could be related to different polymer: fullerene blend morphologies. These results show that supposed small structural alterations such as methoxy substitution already significantly altered the physical properties of the parent polymer and also that oligomers and polymers respond divergent to structural alterations made on a parent structure. View Full-Text
Keywords: organic solar cells; conjugated polymers; DPP; synthesis; Density Functional Theory (DFT) organic solar cells; conjugated polymers; DPP; synthesis; Density Functional Theory (DFT)
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George, Z.; Kroon, R.; Gehlhaar, R.; Gbabode, G.; Lundin, A.; Hellström, S.; Müller, C.; Geerts, Y.; Heremans, P.; Andersson, M.R. The Influence of Alkoxy Substitutions on the Properties of Diketopyrrolopyrrole-Phenyl Copolymers for Solar Cells. Materials 2013, 6, 3022-3034.

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