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Issue 17, 2014
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First principles study of photo-oxidation degradation mechanisms in P3HT for organic solar cells

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Abstract

We present a theoretical study of degradation mechanisms for photoinduced oxidation in organic polymers in the condensed phase, using poly(3-hexylthiophene) (P3HT) as an example. Applying density functional theory with a hybrid density functional and periodic boundary conditions that account for steric effects and permit the modeling of interchain chemical reactions, we investigate reaction pathways that may lead to the oxidation of the thiophene backbone as a critical step toward disrupting the polymer conjugation. We calculate energy barriers for reactions of the P3HT backbone with oxidizing agents including the hydroxyl radical (OH˙), hydroperoxide (ROOH), and the peroxyl radical (ROO˙), following a UV-driven radical reaction starting at the α-carbon of the alkyl side chain as suggested by infrared (IR) and X-ray photoemission (XPS) spectrosocopy studies. The results strongly suggest that an attack of OH˙ on sulfur in P3HT is unlikely to be thermodynamically favored. On the other hand, an attack of a peroxyl radical on the side chain on the P3HT backbone may provide low barrier reaction pathways to photodegradation of P3HT and other polymers with side chains. The condensed phase setting is found to qualitatively affect predictions of degradation processes.

Graphical abstract: First principles study of photo-oxidation degradation mechanisms in P3HT for organic solar cells

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Publication details

The article was received on 11 Jan 2014, accepted on 07 Mar 2014 and first published on 07 Mar 2014


Article type: Paper
DOI: 10.1039/C4CP00146J
Author version available: Download Author version (PDF)
Citation: Phys. Chem. Chem. Phys., 2014,16, 8092-8099
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    First principles study of photo-oxidation degradation mechanisms in P3HT for organic solar cells

    N. Sai, K. Leung, J. Zádor and G. Henkelman, Phys. Chem. Chem. Phys., 2014, 16, 8092
    DOI: 10.1039/C4CP00146J

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