Exploring Halide Perovskite Structural Tunability to Design Materials for Dynamic Photovoltaic Windows

Halide perovskites offer exciting potential as photovoltaic materials and simply as semiconductors. Specifically, their structural tunability has become of greater interest as researchers begin to search for novel ways to tune the materials to achieve improved solar cell stability or to target new applications. One potential technology which halide perovskites could enable is dynamically switchable photovoltaic windows: windows which can transition between photovoltaically active (dark) and non-photovoltaic (transparent). We build toward this goal in this work by investigating the intercalation and deintercalation of methylamine gas into 2-dimensional Ruddlesden-Popper (R-P) phase halide perovskites of the type A₂PbI₄. As has been shown with 3D methylammonium lead iodide films, the intercalation of methylamine into the halide perovskite lattice results in a color change to a clear crystalline phase. We find that in some 2-D perovskite systems, deintercalation of the methylamine gas is incomplete, resulting in the formation of secondary phases including n=2 R-P and 3D perovskites, as well as lower dimensional materials; however, other 2-D perovskite phases show reversible intercalation/deintercalation with methylamine, indicating stronger binding between the long-chain ligand and the lead halide octahedra of the 2-D perovskite sheet. This work reveals the relative affinity of various R-NH₃⁺ molecules, specifically R-C₈H₉-NH₃⁺ materials such as 4-hydroxy phenethyl ammonium, for the halide perovskite lattice and indicates that templating the 3-D CH₃NH₃PbI₃ structure with carefully selected long-chain cations could lead to better reversibility in dynamic photovoltaic windows. Work continues to develop improved guidelines for the design of 2D/3D halide perovskite materials for an array of applications.