Reversible Photochromism in < 110 > Oriented Layered Halide Perovskite

Extending halide perovskites' optoelectronic properties to stimuli-responsive chromism enables switchable optoelectronics, information display, and smart window applications. Here, we demonstrate a band gap tunability (chromism) via crystal structure transformation from three-dimensional FAPbBr(3) to a < 110 > oriented FA(n+)(2)Pb(n)Br(3)(n+2) structure using a mono-halide/cation composition (FA/Pb) tuning. Furthermore, we illustrate reversible photochromism in halide perovskite by modulating the intermediate n phase in the FA(n+)(2)Pb(n)Br(3)(n+2) structure, enabling greater control of the optical band gap and luminescence of a < 110 > oriented mono halide/cation perovskite. Proton transfer reaction-mass spectroscopy carried out to precisely quantify the decomposition product reveals that the organic solvent in the film is a key contributor to the structural transformation and, therefore, the chromism in the < 110 > structure. These intermediate n phases (2 <= n <= infinity) stabilize in metastable states in the FA(n+)(2)Pb(n)Br(3)(n+2) system, which is accessible via strain or optical or thermal input. The structure reversibility in the < 110 > perovskite allowed us to demonstrate a class of photochromic sensors capable of self-adaptation to lighting.