Flexoelectricity in Photoconversion: Fundamentals, Materials, and Outlooks.

Flexoelectricity, the generation of electric polarization by a strain gradient, has recently emerged as a powerful tool for manipulating photoconversion processes in a wide range of materials. This review systematically examines how strain-gradient-induced flexoelectric fields can enhance and tailor both photovoltaic and photoconductive responses, overcoming fundamental limitations of conventional optoelectronic designs. We review key advances across material platforms, including oxide and halide perovskites, two-dimensional semiconductors, with emphasis on mechanisms such as band-structure modulation, carrier separation, and photoconductance tuning under mechanical strain. Experimental demonstrations of giant flexo-photovoltaic coefficients, strain-programmable photodetectors, and flexo-enhanced photocatalytic systems are then surveyed, alongside theoretical insights into the coupling between flexoelectric polarization and photoexcited carriers. Despite the promising progress, significant challenges remain in quantitatively disentangling intrinsic flexoelectric contributions, implementing scalable and controllable strain engineering strategies, and ensuring mechanical robustness under operational conditions. Looking forward, we outline emerging pathways, including freestanding thin films, micro-structured strain architectures, and multifunctional device integration, which harness flexoelectricity to enable adaptive, efficient, and mechanically responsive photoconversion systems for next-generation energy and sensing technologies.