  The thermodynamic limit for the efficiency of solar cells is predominantly
defined by the energy bandgap of the used semiconductor. In case of organic
solar cells both energetics and kinetics of three different species play role:
excitons, charge transfer states and charge separated states. In this work, we
clarify the effect of the relative energetics and kinetics of these species on
the recombination and generation dynamics. Making use of detailed balance, we
develop an analytical framework describing how the intricate interplay between
the different species influence the photocurrent generation, the recombination,
and the open-circuit voltage in organic solar cells. Furthermore, we clarify
the essential requirements for equilibrium between excitons, CT states and
charge carriers to occur. Finally, we find that the photovoltaic parameters are
not only determined by the relative energy level between the different states
but also by the kinetic rate constants. These findings provide vital insights
into the operation of state-of-art non-fullerene organic solar cells with low
offsets.
