Stabilization of Film Morphology in Polymer‐Fullerene Heterojunction Solar Cells

Abstract The fixation of film morphology is essential for the long‐term stability of heterojunction polymer photovoltaic (PV) cells. An epoxy‐functionalized fullerene C60 derivative was synthesized for this purpose. This material can be polymerized at acidic conditions and was found to stabilize the phase‐separated morphologies within blended polythiophene–fullerene heterojunction films. The phase stability of the films was characterized by UV‐VIS spectroscopy and optical microscope. Crosslinkable polythiophene derivatives were also prepared but these materials were much less effective in stabilizing film morphology when mixed into PCBM (C61‐butyric acid methyl ester). Heterojunction polymer PV cells were prepared from these materials and their performance was compared with cells made from conventional materials.