Understanding Physico-Chemical Aspects in the Depth Profiling of Polymer: Fullerene Layers

Supriya Surana, Thierry Conard, Claudia Fleischmann, Jeffrey G. Tait, João P. Bastos, Eszter Voroshazi, Rasmus Havelund, Mathieu Turbiez, Pierre Louette, Alexandre Felten, Claude Poleunis, Arnaud Delcorte, Wilfried Vandervorst

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Layers composed of binary blends of a polymer and a fullerene derivative are at the heart of bulk heterojunction organic photovoltaic cells. The efficiency and stability of these devices critically depend on the distribution of the polymer and fullerene materials within the blend layer. Whereas time-of-flight secondary ion mass spectrometry, particularly in combination with cluster ion beams, has frequently been used to probe similar organic materials, the quantification of the results is often missing due to a lack of understanding of all the parameters influencing the measurement results. This study contributes to improved quantification by exploring the role of the bulk composition and interfacial material on parameters such as sputtering yield, mass fragmentation, and ionization. We show that the argon cluster sputtering yields of these materials may be described by two widely acknowledged sputtering yield relationships. Their fitting parameters depend on the layer composition in a manner that is consistent with a lower energy required for sputtering of layers with higher fullerene derivative content. Similarly, we show that changes in composition impact the ion yields nonlinearly, which is an important source of quantification uncertainty. We provide evidence that, for the case of the fullerene derivative mixed with different donor materials, the matrix effect (i.e., the deviation from a linear response) correlates linearly with the electronegativity of the species in the donor material. Finally, with respect to the quantification of the composition at the interface with the substrate, we present a charge transfer mechanism that describes observed enhancements of the secondary ion intensities. (Graph Presented).

    Original languageEnglish
    Pages (from-to)28074-28082
    Number of pages9
    JournalJournal of Physical Chemistry C
    Volume120
    Issue number49
    DOIs
    Publication statusPublished - 15 Dec 2016

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