Reversible multicolor chromism in layered formamidinium metal halide perovskites

Abstract

Metal halide perovskites feature crystalline-like electronic band structures and liquid-like physical properties. The crystal–liquid duality enables optoelectronic devices with unprecedented performance and a unique opportunity to chemically manipulate the structure with low energy input. In this work, we leverage the low formation energy of metal halide perovskites to demonstrate multicolor reversible chromism. We synthesized layered Ruddlesden-Popper FAn+1PbnX3n+1 (FA = formamidinium, X = I, Br; n = number of layers = 1, 2, 3 … ∞) and reversibly tune the dimensionality (n) by modulating the strength and number of H-bonds in the system. H-bonding was controlled by exposure to solvent vapor (solvatochromism) or temperature change (thermochromism), which shuttles FAX salt pairs between the FAn+1PbnX3n+1 domains and adjacent FAX “reservoir” domains. Unlike traditional chromic materials that only offer a single-color transition, FAn+1PbnX3n+1 films reversibly switch between multiple colors including yellow, orange, red, brown, and white/colorless. Each colored phase exhibits distinct optoelectronic properties characteristic of 2D superlattice materials with tunable quantum well thickness.

New Variants of (110)‐Oriented Layered Lead Bromide Perovskites, Templated by Formamidinium or Pyrazolium

“…For example, since FA is sufficiently small to occupy the A-site in a 3D perovskite, it can also be used as a 'perovskitiser' to template the formation of Ruddlesden-Popper-like 2D perovskites of generic compositions (A) m (FA) n-1 Pb n X 3n + 1 (m = 1,2; n = 2,3,4…) where FA occupies exclusively the perovskite-like Asite rather than the larger, more flexible interlayer site. [7,8] More intriguingly, FA has also been shown to encourage formation of the much less common "(110)-cut" layered perovskite structure. Thus, both (HEA)(FA)PbBr 4 [9] (HEA = hydroxyethylammonium) and (FA)(GA)PbI 4 [10] (GA = guanidinium) have been reported to adopt (110)-like LHP structures.…”

Formamidinium-based Ruddlesden–Popper perovskite films fabricated via two-step sequential deposition: quantum well formation, physical properties and film-based solar cells

“…550 nm, which were assigned to FA 2 FA nÀ1 Pb n I 3n+1 perovskites with n = 2 and n = 3 phases according to the previous report for FA n+1 Pb n I 3n+1 powder produced via ball-milling. 36 Although the existence of FA 2 FA nÀ1 Pb n I 3n+1 has been predicted, 37 not much is known about these materials. To better understand the growth of FA 2 FA nÀ1 Pb n I 3n+1 during film fabrication, we fabricated FA 2 FA nÀ1 Pb n I 3n+1 films using two-step sequential deposition by introducing neat FAI on the PbI 2 film, or FA 2 FA nÀ1 Pb n I 3n+1 powders using ball-milling from FAI : PbI 2 powders without the solvent, or FA 2 FA nÀ1 Pb n I 3n+1 films via one-step spin-coating from the DMSO solvent.…”

Structural Transitions and Stability of FAPbI3 and MAPbI3: The Role of Interstitial Water

“…In that case the change of stoichiometry n is proposed to occur through the diffusion of FAI among grains. No appearance of the n H perovskite structures was found in that case [ 60 ], and we assume that, symmetrically, no layered perosvkites appear as intermediate structures of cubic FAPI.…”

“…The evidence of this is the fact that moderate pressure (0.4 GPa) induces the transformation of the yellow 2H phase into orange 4H and red 6H structures, stable, or at least metastable over a long time span, at room temperature [ 19 ]. Another type of reversible transformations among layered perovskite structures, again with colours ranging from yellow to red, has been found in layered Ruddlesden-Popper FA Pb I films exposed to humidity [ 60 ]. In that case the change of stoichiometry n is proposed to occur through the diffusion of FAI among grains.…”