Lateral phase separation gradients in spin-coated thin films of high-performance polymer: fullerene photovoltaic blends

Lintao Hou, Ergang Wang, Jonas Bergqvist, B. Viktor Andersson, Zhongqiang Wang, Christian Muller, Mariano Campoy-Quiles, Mats R. Andersson, Fengling Zhang, Olle Inganas

    Research output: Contribution to journalArticlepeer-review

    51 Citations (Scopus)

    Abstract

    In this study, it is demonstrated that a finer nanostructure produced under a rapid rate of solvent removal significantly improves charge separation in a high-performance polymer:fullerene bulk-heterojunction blend. During spin-coating, variations in solvent evaporation rate give rise to lateral phase separation gradients with the degree of coarseness decreasing away from the center of rotation. As a result, across spin-coated thin films the photocurrent at the first interference maximum varies as much as 25%, which is much larger than any optical effect. This is investigated by combining information on the surface morphology of the active layer imaged by atomic force microscopy, the 3D nanostructure imaged by electron tomography, film formation during the spin coating process imaged by optical interference and photocurrent generation distribution in devices imaged by a scanning light pulse technique. The observation that the nanostructure of organic photovoltaic blends can strongly vary across spin-coated thin films will aid the design of solvent mixtures suitable for high molecular-weight polymers and of coating techniques amenable to large area processing.

    Original languageEnglish
    Pages (from-to)3169-3175
    Number of pages7
    JournalAdvanced Functional Materials
    Volume21
    Issue number16
    DOIs
    Publication statusPublished - 23 Aug 2011

    Keywords

    • evaporation rate
    • organic photovoltaics
    • phase separation
    • solar cells
    • spin coating

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