Surface termination and strain-induced modulation of the structure and electronic properties in 2D perovskites (Cs2BCl4 & CsB2Cl5, B = Pb, Sn): a first-principles study

Abstract

Two-dimensional (2D) halide perovskites have demonstrated impressive long-term stability and superior device performance as compared to their three-dimensional (3D) counterparts. The potential of 2D halide perovskites for advanced photovoltaic applications can be enhanced by an understanding of how external factors like strain could be used to tune their optoelectronic properties. This study explores the effects of biaxial strain on the structure and electronic transport properties of 2D halide perovskites, focusing on the lowest energy (001) surfaces of (Cs₂BCl₄ and CsB₂Cl₅, B = Pb or Sn) with CsCl and BCl₂ terminations. Using first-principles calculations, we find that the lower energy CsCl terminated surface, resulting in Cs₂BCl₄, couples strongly with biaxial strain. This termination shows bandgap modulations from approximately 1.5 eV to 1.8 eV for Cs₂PbCl₄ and 1.2 eV to 1.5 eV for Cs₂SnCl₄ with biaxial strain. Within the acoustic deformation potential theory, we compute hole mobilities, and find substantial enhancements of approximately 80% for Pb-based and 50% for Sn-based systems, thereby emphasizing the potential of strain engineering to further optimize charge transport properties in 2D halide perovskites.