Observation and investigation of a dynamic inflection point in current-voltage curves for roll-to-roll processed polymer photovoltaics

Andrew James Medford, Mathilde Raad Lilliedal

    Research output: Chapter in Book/Report/Conference proceedingConference abstract in proceedingsResearch


    Inflection point behaviour is often observed in the current-voltage (IV) curve of polymer and organic solar cells. This phenomenon is examined in the context of flexible roll-to-roll (R2R) processed polymer solar cells in a large series of devices with a layer structure of: PET-ITO-ZnO-P3HT:PCBM-PEDOT:PSS-Ag. The devices were manufactured using a combination of slot-die coating and screen printing; they were then encapsulated by lamination using a polymer based barrier material. All manufacturing steps were carried out in ambient air. The freshly prepared devices showed a consistent inflection point in the IV curve and a corresponding poor performance or lack of photovoltaic behaviour. Upon exposure to 1000 Wm-2 illumination at ca. 85 oC and repeated IV scans (photo-annealing) the inflection point gradually disappeared, and performance drastically increased over time. The characteristics and stability of this “photo-annealing” behaviour was further investigated by studying the effects of several key factors: temperature, illumination, and atmosphere. The results consistently showed that the inflection point is a dynamic interface phenomenon which can be removed under specific conditions. Subsequently, chemical characterization of device interfaces was carried out in order to identify possible chemical processes that are related to photo-annealing. A possible mechanism based on ZnO photoconductivity, photooxidation and redistribution of oxygen inside the cell is proposed, and it is anticipated that the findings are applicable to various other device structures based on semiconducting oxides. The findings may have influences on the possibilities and scale-up of polymer solar technologies.
    Original languageEnglish
    Title of host publicationBook of abstracts
    PublisherDanmarks Tekniske Universitet, Risø Nationallaboratoriet for Bæredygtig Energi
    Publication date2010
    Publication statusPublished - 2010
    Event3rd International Summit on OPV Stability - Risø, Denmark
    Duration: 21 Oct 201029 Oct 2010
    Conference number: 3


    Conference3rd International Summit on OPV Stability
    Internet address


    • Polymer solar cells
    • Solar energy


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