  Surface recombination has a major impact on the open-circuit voltage
($V_\text{oc}$) of organic photovoltaics. Here, we study how this loss
mechanism is influenced by imbalanced charge transport in the photoactive
layer. As a model system, we use organic solar cells with a two orders of
magnitude higher electron than hole mobility. We find that small variations in
the work function of the anode have a strong effect on the light intensity
dependence of $V_\text{oc}$. Transient measurements and drift-diffusion
simulations reveal that this is due to a change in the surface recombination
rather than the bulk recombination. We use our numerical model to generalize
these findings and determine under which circumstances the effect of contacts
is stronger or weaker compared to the idealized case of balanced charge
transport. Finally, we derive analytical expressions for $V_\text{oc}$ in the
case that a pile-up of space charge is present due to highly imbalanced
mobilities.
