Photochemical stability and photovoltaic performance of low-band gap polymers based on dithiophene with different bridging atoms

Martin Helgesen, Thomas J. Sørensen, Matthieu Manceau, Frederik C Krebs

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    New low-band gap polymers based on dithienylbenzothiadiazole (DBT) and dithiophene with different bridging atoms have been synthesized and explored in a comparative study on the photochemical stability and photovoltaic performance. Two differently modified DBT units were exploited, namely 5,6- bis(tetradecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DBT1) and 4,7-bis(4-dodecylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (DBT2). In thin films the polymers had optical band gaps in the range of 1.51-1.70 eV where the DBT2 based polymers are red shifted 61-81 nm compared to the DBT1 based polymers indicating greater interchain packing when the side chains are situated on the thienyl groups compared to on the benzothiadiazole unit. The best photovoltaic devices based on blends of polymer and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were prepared with polymers based on the DBT1 unit giving efficiencies up to 2.3%. The photochemical stability was measured by the amount of absorbed photons under 1 sun versus the ageing time for each polymer, which clearly shows that the two polymers containing a 4,4-bis(2-ethylhexyl)-4H- cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT) unit are by far the most unstable. Substitution of the bridging carbon atom with silicon results in a significant stability improvement by a factor 5. © 2011 The Royal Society of Chemistry.
    Original languageEnglish
    JournalPolymer Chemistry
    Volume2
    Issue number6
    Pages (from-to)1355-1361
    ISSN1759-9954
    DOIs
    Publication statusPublished - 2011

    Bibliographical note

    This work was supported by the Danish Strategic Research
    Council (DSF 2104-05-0052 and 2104-07-0022)

    Keywords

    • Polymer solar cells

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