Principles of Selective Stacking 2D‐SnS on FAPbI₃ to Form Directional Polarity for Low‐Cost Solar Energy Conversion

Abstract Metal halide perovskites have been extensively studied due to their exceptional optoelectronic properties. However, the fabrication of perovskite solar cells (PSCs) has been hindered by the poor stability and high costs of hole transport layers (HTLs) such as Spiro‐OMeTAD. 2D materials, which can be stacked via van der Waals (vdW) forces to form heterostructures, open up new possibilities for atomic‐scale engineering of perovskite devices. In this study, the electronic, optical properties of the FAPbI 3 /SnS‐vdW heterostructure are investigated using first‐principles calculations. The SnS monolayer and the FAPbI 3 surface form a stable Type‐II heterostructure with a smaller bandgap compared to their individual components. Through selective stacking of 2D‐SnS at PbI 2 or FAI interfacial atoms, the charge transfer direction is changed accordingly. The favorable interfacial polarity, smaller distance, and stronger bonding of SnS/PbI 2 interface result in a better HTL properties. Simulations demonstrate that FAPbI 3 /SnS‐based PSCs achieves a power conversion efficiency (PCE) of 21.30%, comparable to the traditional FAPbI 3 /Spiro‐OMeTAD structure. Moreover, interfacial effects enhance the optical absorption of the FAPbI 3 /SnS heterojunction, thus, the SnS‐based PSC exhibits a high external quantum efficiency (EQE) with an extended absorption range. This work provides a novel perspective, designing principles for fabricating low‐cost, high‐performance PSCs based on vdW heterostructures.