Chad Snyder - Influence of substrate on crystallization in polythiophene/fullerene blends

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      Publication Details (including relevant citation   information):

      C. He, D.S. Germack, R.J. Kline, D.M. DeLongchamp, D.A. Fischer,   C.R. Snyder, M.F. Toney, J.G. Kushmerick, L.J. Richter, Solar   Energy Materials & Solar Cells 95,   1375-1381 (2011).


      The nanoscale morphology of the active layer in organic, bulk   heterojunction (BHJ) solar cells is crucial to device   performance. Often a combination of casting conditions and post   deposition thermal treatment is used to optimize the morphology.   In general, the development of microscopic crystals is   deleterious, as the exciton diffusion length is ~10 nm. We find   that the microscopic crystallization behavior in   polythiophene/fullerene blends is strongly influenced by the   substrate on which the BHJ is cast. With a silicon oxide   substrate, the crystal nucleation density is high and significant   crystallization occurs at a temperature of 140 C. On more   hydrophobic substrates, significantly higher temperatures are   required for observable crystallization. This difference is   attributed to the interfacial segregation of the PCBM,
      controlled by the substrate surface energy. The substrate   dependence of crystallization has significant implications on the   fullerene crystal growth mechanisms and practical implications   for device studies.

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