Mixed-halide copper-based perovskite R2Cu(Cl/Br)4 with different organic cations for reversible thermochromism.

Two-dimensional (2D) hybrid perovskites have exhibited multiple features owing to their multiple quantum well structure. Here, we show the synthesis and characterization of 2D mixed-halide Cu-based perovskite crystals, R2Cu(Cl/Br)4, with three different alkyl chains, where R is methyl, butyl, or hexyl ammonium cations. Exfoliated perovskite flakes exhibit reversible thermochromism with changes in color darkness with temperature variation. Differential scanning calorimetry and temperature-dependent X-ray diffraction measurements reveal that the thermochromic behavior mechanism of R2Cu(Cl/Br)4 depends on the nature of the alkyl chain. [ABSTRACT FROM AUTHOR]