Understanding the role of spacer cation in 2D layered halide perovskites to achieve stable perovskite solar cells

Abstract

Intercalation of a large organic cation between metal halide layers provides better energetic stability to the perovskite structure. In this regard large organic cation intercalated two-dimensional layered halide perovskites (2D-LHPs) are receiving research attention due to their improved environmental stability and structural versatility. Here, we present a detailed theoretical investigation on the effect of spacer cations on the structural distortion of the inorganic layer that mainly controls the band edge properties of 2D-LHPs. We have considered pure 2D-LHP systems that include three mono-cation as well as four di-cation spacers. The 2D-LHP systems are A₂PbI₄ and APbI₄ for mono-cation and di-cation spacers, respectively, where A is the ammonium based organic spacer cation. Moreover, the structural, electronic, and optical properties of the 2D-LHPs have been investigated in detail to determine the origin of the spacer cation influence on the properties of 2D-LHPs. In spite of the mono-cationic nature, the 3-APN spacer cation considered in our study provides exceptionally reduced octahedral distortion (Pb–I–Pb angle ∼177° and 172°) and inorganic layer separation (∼10.17 Å) that results in a reduced band gap and good charge carrier masses. Directional anisotropy observed in the transport as well as optical property will guide the fabrication of high-performance photovoltaic devices. The considered di-cationic systems also possess an impressive band gap, carrier effective mass and optical absorption. Our findings expose the scope of mono-cation based systems as an excellent choice of material for applications in photovoltaics. Therefore, our study finds a design approach for 2D-LHPs to tune their properties through spacer cation engineering for application in photovoltaic devices.