Manipulating Barocaloric Effects in Two-Dimensional Metal–Halide Perovskites through Compositional Engineering

Abstract

The cooling sector is projected to become one of the largest drivers of climate change in the next few decades. Barocaloric materials, which undergo thermal changes in response to hydrostatic pressure, have the potential to replace environmentally-damaging vapor-compression refrigeration with next-generation solid-state cooling at scale. To be competitive, these materials must undergo phase transitions with a large entropy change, low thermal hysteresis, and high sensitivity to pressure. However, the structure–property relationships that govern solid-state phase transitions are not well understood. My goal in this thesis is to provide fundamental insights into the chemical factors that influence phase-change thermodynamics, which will aid in the design of effective barocaloric materials. Two-dimensional metal–halide perovskites are highly tunable materials that exhibit promising barocaloric properties. Here, I manipulated the organic-inorganic interfaces and organic bilayers of 2-D perovskites through halide and cation engineering to connect the chemical and structural factors of these materials to their phase-change thermodynamics and kinetics. With these structure–property relationships, I could then develop design principles to address the challenges of leveraging 2-D perovskites for barocaloric cooling, namely the presence of multiple phase transitions and tradeoffs between entropy and reversibility. Our results demonstrate that compositional engineering in 2-D perovskites is an effective chemical strategy for driving a collective response of the order–disorder transition, consequently minimizing the effect of hysteresis without compromising entropy. These insights deepen our fundamental understanding of order–disorder transitions, and will help advance the development of alternative cooling technologies to address the urgent need for sustainable and equitable cooling for a growing population in a warming world.