  One of the most significant features of lead-halide perovskites are their
ability to have comparably slow recombination despite the fact that these
materials are mostly processed from solution at room temperature. The slow
recombination allows achieving high open-circuit voltages when the lead-halide
perovskite layers are used in solar cells. This perspective discusses the state
of the art of our understanding and of experimental data with regard to
recombination and open-circuit voltages in lead-halide perovskites. A special
focus is put onto open questions that the community has to tackle to design
future photovoltaic and optoelectronic devices based on lead-halide perovskites
and other semiconductors with similar properties.
