Stable and rapid thermochromic reversibility in acene alkylamine intercalated layered hybrid perovskites

Since the discovery of thermochromism in halide perovskites, new perovskite materials with excellent thermochromic properties have been developed. Among them, two-dimensional (2D) layered hybrid perovskites have been extensively explored because of their highly tunable structures and unique thermochromic responses. In this study, the thermochromism in acene alkylamine-spaced 2D perovskite single crystals (PEA)2PbI4 and (NEA)2PbI4 (PEA = 2-phenylethylammonium, NEA = 2-(2-naphthyl)-ethanammonium) is studied. These 2D perovskites undergo a distinct color change between orange and red during heating and cooling cycles, with the corresponding optical bandgap modulation monitored by variable-temperature absorption spectroscopy. The thermochromism in (PEA)2PbI4 and (NEA)2PbI4 is caused by lattice expansion, as confirmed by thermogravimetric–differential scanning calorimetry and variable-temperature powder X-ray diffraction. Compared with the thermochromism caused by structural phase transition, lattice-expansion-modulated thermochromism demonstrates rapid color change and luminescence recovery, and enhanced thermal cycling stability. This study presents a new strategy for developing thermochromic halide perovskites for multifunctional applications.