Dynamic disentanglement of photoflexoelectricity and flexophotovoltage

The coupling between light and strain gradients shows two kinds of effects: light enhanced flexoelectricity (photoflexoelectricity) and gradient enhanced photovoltage (flexophotovoltage). Although these effects originate from fundamentally different physical mechanisms (one is light enhanced electromechanical coupling, the other is a bulk photovoltaic effect), in this article we show that dynamic flexoelectric measurements of semiconductors under illumination intrinsically contain contributions from both. To allow disentangling them, we have developed a general theoretical framework for their combined response in oscillating systems, demonstrating that the two contributions can be unambiguously separated through their distinct frequency and phase dependencies. We have validated these predictions using oscillating cantilever measurements on centrosymmetric perovskite semiconductors (SrTiO3 and methylammonium lead bromide, MAPbBr3), obtaining selfconsistent values for the coefficients both effects which are in excellent agreement with independent static measurements. Our results establish a general protocol for disentangling both light strain gradient couplings using only oscillatory measurements, and clarify the interpretation of flexoelectric measurements under illumination.