  A typical signature of charge extraction in disordered organic systems is
dispersive transport, which implies a distribution of charge carrier mobilities
that negatively impact on device performance. Dispersive transport has been
commonly understood to originate from a time-dependent mobility of hot charge
carriers that reduces as excess energy is lost during relaxation in the density
of states. In contrast, we show via photon energy, electric field and film
thickness independence of carrier mobilities that the dispersive photocurrent
in organic solar cells originates not from the loss of excess energy during hot
carrier thermalization, but rather from the loss of carrier density to trap
states during transport. Our results emphasize that further efforts should be
directed to minimizing the density of trap states, rather than controlling
energetic relaxation of hot carriers within the density of states.
