Interlayer Ordered Mixed-Spacer 2D Halide Perovskites

Two-dimensional (2D) halide perovskites exhibit extraordinary stability and structural tunability because they can incorporate different organic cations as spacers. Their structures can be divided into the Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases depending on the spacers. When different spacers are mixed into one perovskite structure, they are usually disordered and occupy the same interlayer space. In this work, we demonstrate that when cyclic 1,2,4-triazolium (Tz) is used as a spacer and combined with another linear spacer such as propylammonium (PA) or butylammonium (BA), the interlayer ordered mixed-spacer 2D perovskites can form. The Tz and PA (BA) spacers occupy separate interlayer spaces and show two different interlayer distances. The octahedra next to the Tz spacers resemble the stacking of the DJ phase while those adjacent to the PA (BA) layers exhibit the stacking of the RP phase. The bandgaps of (PA)(Tz)PbBr₄and (BA)(Tz)PbBr₄ are in between the parent <i>n </i>= 1 compounds ((PA)₂PbBr₄or (BA)₂PbBr_{4 ,}and (Tz)₂PbBr₄). DFT calculations suggest that the band structures of (PA)(Tz)PbBr₄and (BA)(Tz)PbBr₄combine features from parent compounds yet differ from a simple superposition. This way, we are able to combine the properties of different spacers (cyclic and linear, aromatic and aliphatic) in one structure. This work expands the structure types in 2D perovskites and suggests many possible combinations of spacer cations for all kinds of optoelectronic applications.