Stabilization of film morphology in polymer-fullerene heterojunction solar cells

The fixation of film morphology is essential for the long-term stability of heterojunction polymer photovoltaic (PV) cells. An epoxy-functionalized fullerene C-60 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.