We present direct spectroscopic evidence for substantial subnanosecond charge recombination in polymer-polymer blend photovoltaic devices. Early dynamics are dominated by exciton-charge interactions associated with high initial excitation densities. Independent of density, 30% of charges subsequently recombine geminately within just 2 nanoseconds, in contrast with fullerene blends. The remainder recombines with a half-life of $\sim 200\mathrm{ns}$. The morphological invariance of subnanosecond recombination suggests that its origin is inherent in the molecular structure at the polymer-polymer interface.

• Received 13 December 2009

DOI:https://doi.org/10.1103/PhysRevLett.104.177701