Shining Light on Flexoelectricity

Flexoelectricity, being a universal property, can be used to polarize all sorts of materials, from insulators to metals and of course semiconductors. In turn, this gradient-induced polarization can couple to other material properties, including their reaction to light. Two such coupled interactions are confusingly similar in name, but rather different in nature: the photo-flexoelectric effect, whereby photocarriers enhance the flexoelectricity of illuminated materials, and the flexo-photovoltaic effect, whereby flexoelectricity enables or enhances the photovoltaic output of semiconductors. In my talk I will discuss the differences between these two effects, including their relative advantages and drawbacks from a functional point of view. I will use halide perovskites and other photo-sensitive semiconductors to illustrate the magnitude of these two effects, and in particular the ability of the flexophotovoltaic effect to induce bigger-than-bandgap photovoltages and enhanced efficiencies in perovskite solar cells under bending.