Subnanosecond Geminate Charge Recombination in Polymer-Polymer Photovoltaic Devices

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 similar to 200 ns. The morphological invariance of subnanosecond recombination suggests that its origin is inherent in the molecular structure at the polymer-polymer interface.