Factors Governing Intercalation of Fullerenes and Other Small Molecules Between the Side Chains of Semiconducting Polymers Used in Solar Cells

While recent reports have established signifi cant miscibility in polymer:fullerene blends used in organic solar cells, little is actually known about why polymers and fullerenes mix and how their mixing can be controlled. Here, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and molecular simulations are used to study mixing in a variety of polymer:molecule blends by systematically varying the polymer and smallmolecule properties. It is found that a variety of polymer:fullerene blends mix by forming bimolecular crystals provided there is suffi cient space between the polymer side chains to accommodate a fullerene. Polymer:tetrafl uoro-tetracyanoquinodimethane (F4-TCNQ) bimolecular crystals were also observed, although bimolecular crystals did not form in the other studied polymer:nonfullerene blends, including those with both conjugated and non-conjugated small molecules. DSC and molecular simulations demonstrate that strong polymer-fullerene interactions can exist, and the calculations point to van der Waals interactions as a signifi cant driving force for molecular mixing. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Citation

Miller NC, Cho E, Gysel R, Risko C, Coropceanu V, et al. (2012) Factors Governing Intercalation of Fullerenes and Other Small Molecules Between the Side Chains of Semiconducting Polymers Used in Solar Cells. Adv Energy Mater 2: 1208–1217. Available: http://dx.doi.org/10.1002/aenm.201200392.

Sponsors

This work was supported by the Center for Advanced Molecular Photovoltaics (Award No KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST). Work at Georgia Tech was also supported by the Office of Naval Research (N00014-11-1-0211). The authors would like to acknowledge Darin Laird of Plextronics and Jeremy E.P. Dahl for the synthesis and purification of the indene-C60 fullerenes and the diamondoids, respectively. We would also like to acknowledge D.F. Kavulak and Jean M.J. Frechet of the University of California in Berkeley and Martin Drees of Luna Innoations for the synthesis of the dihydronaphthyl bridged ester fullerene derivatives and the LUPCBEH-C80, respectively. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences. We acknowledge the permission to use the diffraction image processing and data analysis software package Wxdiff by Stefan C.B. Mannsfeld at SSRL (http://code.google.com/p/wxdiff).