  Halide perovskites have outstanding photovoltaic properties which have been
optimized through interfacial engineering. However, as these materials approach
the limits imposed by the physics of semiconductor junctions, it is urgent to
explore alternatives, such as the bulk photovoltaic effect, whose physical
origin is different and not bound by the same limits. In this context, we focus
on the flexo-photovoltaic effect, a type of bulk photovoltaic effect that was
recently observed in oxides under strain gradients. We have measured the
flexo-photovoltaic effect of MAPbBr3 and MAPbI3 crystals under bending and
found it to be orders of magnitude larger than for SrTiO3, the benchmark
flexo-photovoltaic oxide. For sufficiently large strain gradients,
photovoltages bigger than the bandgap can be produced. Bulk photovoltaic
effects are additive and, for MAPbI3, the flexo-photovoltage exists on top of a
native bulk photovoltage that is hysteretic, consistent with the electrically
switchable macroscopic polarization of this material. The results suggest that
harnessing the flexo-photovoltaic effect through strain gradient engineering
can provide a functional leap forward for halide perovskites.
