  Hall effect measurements are important for elucidating the fundamental charge
transport mechanisms and intrinsic mobility in organic semiconductors. However,
Hall effect studies frequently reveal an unconventional behavior that cannot be
readily explained with the simple band-semiconductor Hall effect model. Here,
we develop an analytical model of Hall effect in organic field-effect
transistors in a regime of coexisting band and hopping carriers. The model,
which is supported by the experiments, is based on a partial Hall voltage
compensation effect, occurring because hopping carriers respond to the
transverse Hall electric field and drift in the direction opposite to the
Lorentz force acting on band carriers. We show that this can lead in particular
to an underdeveloped Hall effect observed in organic semiconductors with
substantial off-diagonal thermal disorder. Our model explains the main features
of Hall effect in a variety of organic semiconductors and provides an
analytical description of Hall mobility, carrier density and carrier coherence
factor.
