  Ferroelectric all-inorganic halide perovskites nanocrystals with both
spontaneous polarizations and visible light absorption are promising candidates
for designing functional ferroelectric photovoltaic devices. Three dimensional
halide perovskite nanocrystals have the potential of being ferroelectric, yet
it remains a challenge to realize ferroelectric photovoltaic devices which can
be operated in absence of an external electric field. Here we report that a
popular all-inorganic halide perovskite nanocrystal, CsPbBr3, exhibits
ferroelectricity driven photovoltaic effect under visible light in absence of
an external electric field. The ferroelectricity in CsPbBr3 nanocrystals
originates from the stereochemical activity in Pb (II) lone pair that promotes
the distortion of PbBr6 octahedra. Furthermore, application of an external
electric field allows the photovoltaic effect to be enhanced and the
spontaneous polarization to be switched with the direction of the electric
field. Robust fatigue performance, flexibility and prolonged photoresponse
under continuous illumination are potentially realized in the zero-bias
conditions. These finding establishes all-inorganic halide perovskites
nanocrystals as potential candidates for designing novel photoferroelectric
devices by coupling optical functionalities and ferroelectric responses.
