Shift‐Current Photovoltaics Based on a Non‐Centrosymmetric Phase in In‐Plane Ferroelectric SnS

The shift‐current photovoltaics of group‐IV monochalcogenides has been predicted to be comparable to those of state‐of‐the‐art Si‐based solar cells. However, its exploration has been prevented from the centrosymmetric layer stacking in the thermodynamically stable bulk crystal. Herein, the non‐centrosymmetric layer stacking of tin sulfide (SnS) is stabilized in the bottom regions of SnS crystals grown on a van der Waals substrate by physical vapor deposition and the shift current of SnS, by combining the polarization angle dependence and circular photogalvanic effect, is demonstrated. Furthermore, 180° ferroelectric domains in SnS are verified through both piezoresponse force microscopy and shift‐current mapping techniques. Based on these results, an atomic model of the ferroelectric domain boundary is proposed. The direct observation of shift current and ferroelectric domains reported herein paves a new path for future studies on shift‐current photovoltaics. A non‐centrosymmetric layer stacking phase of 2D tin sulfide (SnS) is successfully achieved on van der Waals substrates and the shift current in SnS is demonstrated. Following the PFM observation that reveals the existence of ferroelectric domains, an atomic model of the ferroelectric domain boundary is proposed.