We developed an hybrid organic-inorganic composite consisting of a 2D perovskite and a copolymer. At room temperature the composite is highly transparent in the visible region with transmittance > 90%. At higher temperatures, the movement of the polymer chains releases the precursors, allowing the perovskite formation, which results in a colored film. The color changes according to the ‘n’ value of the PVK. PVK with n=1 starts coloring at 70°C, achieving a ∆Tmax = 91.5% at 510 nm. On the other hand, PVK with n=2 and 3 starts coloring only at 120°C achieving a ∆Tmax = 90.5% and 91.8% at 577 nm and 618 nm, respectively. The process is fully reversible: once the temperature has been lowered, the polymer again intercalates PVK reagents, going back to the transparent phase. The times required for coloring and bleaching are in the order of tens of seconds.
One of the main innovative aspects of the developed composite lies in the mechanism of its thermochromism. Hybrid perovskite-based thermochromic systems already known in the literature show this phenomenon following the adsorption and desorption of volatile molecules, therefore it is necessary to use a controlled atmosphere to observe the color transition as a function of temperature. Instead, the thermochromism of the developed composite material depends on perovskite assembly and disassembly processes induced by the presence of a polymeric chain. As a result, the system works in normal environmental conditions, thus showing greater versatility. Another innovative aspect of the present technology is represented by the possibility of controlling the color and the transition temperature of the thermochromic film without the need for complex synthesis processes or complicated and expensive deposition processes.
Italy