  We suggest universal expressions for the rates of charge transition between
molecules in organic disordered semiconductors, which differ between electrons
and holes. The donor and acceptor molecules (monomers) are represented in terms
of their frontier orbitals, with asymptotic tails reflecting the different
asymptotic potential wells which bind different charge carriers. This model
predicts an asymmetry of the tunnel factors and the interaction with phonon
field with respect to electrons and holes, leading to different formulas for
the transition rates and the thermal mobility of the different charge carriers.
This is demonstrated explicitly for transitions between organic molecules
initiated by fluctuations of the inter-molecular distance due to deformation of
by the phonon field, but the asymmetry between the carriers is universal and
should be essential for quantitative analysis of charge transport in any
disordered material. In particular, in the framework of classical Mott
considerations our result predict an unusual temperature dependence of holes
mobility, $\sim (T_0/T)^r \exp -( T_0/T)^{1/4}$, where $r = ( E_F^h)^{-1/2}$,
and $E_F^h$ is the energy of hole at the Fermi level in atomic units.
