Linear Bulk Photovoltaic Effect in Strain Gradient-Engineered MoS₂

The theoretical Shockley-Queisser limit of photon-electricity conversion in conventional <i>p-n</i> junction could be potentially overcome by the bulk photovoltaic effect that uniquely occurs in non-centrosymmetric materials. Using strain gradient engineering, the flexo-photovoltaic effect, i.e., strain gradient-induced bulk photovoltaic effect, can be activated in centrosymmetric semiconductors significantly expanding material choices for future sensing and energy applications. Here, we propose a strain gradient engineering approach based on the structural inhomogeneity and phase transition of a two-dimensional/three-dimensional (2D/3D) hybrid system. We report an experimental demonstration of the flexo-photovoltaic effect in an archetypal 2D material MoS₂ transferred on a VO₂ microbeam. The experimental bulk photovoltaic coefficient in MoS₂ is orders of magnitude higher than that in most non-centrosymmetric materials. Our findings unveil the fundamental relation between the flexo-photovoltaic effect and a strain gradient in low-dimensional materials, which could potentially inspire the exploration of novel optoelectronic phenomena in strain gradient-engineered materials. The MoS₂/VO₂ hybrid structure sheds light on emerging phenomena and brings new opportunity in 2D/3D interfaces.