Operando Imaging of Crystallinity-Dependent Multicolor Thermochromic Processes for Single Hydrated Hybrid Perovskite Particles.

The thermochromic properties of hydrated metal halide perovskites (MHPs) are promising for applications in smart windows, solar cells, optical sensors, and information storage. Traditional ensemble characterization methods always study the averaged thermochromic activity, lacking the accurate structure-activity correlation. Here we utilize dark-field microscopy (DFM) to in situ image the thermochromic processes of single isolated hydrated hybrid perovskite (CH 3 NH 3 ) 4 PbI 6- x Cl x ·2H 2 O (MA 4 PbI 6- x Cl x ·2H 2 O) microparticles. The thermal-induced dehydration transition is demonstrated to alter the color of single MA 4 PbI 6- x Cl x ·2H 2 O particles. Operando single-particle mapping results reveal the significant intra- and interparticle variations of thermochromic behaviors, yielding unexpected single or multistep multicolor thermochromic processes. These phenomena are confirmed to be governed by the crystallinity of single MA 4 PbI 6- x Cl x ·2H 2 O particles that results in distinct composition-dependent bandgaps and thermal decomposition pathways. The present work highlights the important role of single-particle imaging for resolving the intrinsic thermochromic characteristic of hydrated MHPs, therefore opening a way for rational design of stimuli-responsive materials.