Efficient charge separation in organic photovoltaics through incoherent   hopping
  We demonstrate that efficient and nearly field-independent charge separation in organic planar heterojunction solar cells can be described by an incoherent hopping mechanism. We model the separation efficiency of electron-hole pairs created at donor-acceptor organic interfaces. By using kinetic Monte Carlo simulations that include the effect of on-chain delocalization we show that efficient charge extraction to the electrodes requires bipolar transport and increased dimensionality. This model explains experimental results of almost field independent charge separation in some molecular systems and provides important guidelines at the molecular level for maximizing the efficiencies of organic solar cells. 
Stavros Athanasopoulos, Steffen Tscheuschner, Heinz B\"assler and Anna   K\"ohler
cond-mat.mes-hall