Pressure and temperature are the most common thermodynamic parameters used to define the phase diagram of stable states of matter. Herein we explore nanostructuring as a means to access forbidden regions of the bulk pressure-temperature phase diagram. Cesium lead iodide, CsPbI3 is an excellent candidate material to test if reduced physical dimensions alone can render its high-temperature, optoelectronically functional perovskite phase the equilibrium polymorph under standard conditions. We synthesized CsPbI3 in the voids of 3-D nano-architectured silica inverse opal scaffolds. Thereby, we were able to compare the phase transition sequence of nanoconfined CsPbI3 with confinement dimensions ranging from a few nanometers to mesoscopic dimensions. Due to the large surface energy contribution in the resulting composite, it is critical to isolate and study the individual influences of crystal size and chemical identity of the interface to the phase stability. To do so we systematically functionalized the surface of the scaffold with polar and non-polar silane self-assembled monolayers (SAMs) to gauge the extent to which surface energy impacts the phase stability. We found a 270 C drop in the phase transition temperature and enhanced thermal stability as a consequence of nanoconfinement. In contrast we observed that the chemical identity of the perovskite-scaffold interface had no significant effect on the structural stability, while nonetheless exerting a significant impact on the electronic properties of CsPbI3.

Does interfacial energy contribute to the stabilization of 3D-nanostructured perovskite phase CsPbI3?

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.