  In this review, we present and discussed the main trends in photovoltaics
with emphasize on the conversion efficiency limits. The theoretical limits of
various photovoltaics device concepts are presented and analyzed using a
flexible detailed balance model where more discussion emphasize is toward the
losses. Also, few lessons from nature and other fields to improve the
conversion efficiency in photovoltaics are presented and discussed as well.
From photosynthesis, the perfect exciton transport in photosynthetic complexes
can be utilized for PVs. Also, we present some lessons learned from other
fields like recombination suppression by quantum coherence. For example, the
coupling in photosynthetic reaction centers is used to suppress recombination
in photocells.
