(508c) 2D Halide Perovskites As Color-Changing Semiconductors

Metal halide perovskites have become a widely studied class of semiconductors with broadly tunable properties. Typical metal halide perovskites have an AMX₃ stoichiometry and a 3 dimensional [MX₆]^2- octahedral structure, but this corner-sharing octahedral network can also be exfoliated by long-chain organic cations to form 2 dimensional [MX₆]^2- octahedral sheets. The combination of structural flexibility with the defect tolerance has led to high performing solution-processed optoelectronic devices (e.g., solar cells, LEDs, x-ray detectors).

Most semiconductors are unable to change color-state on demand; however, metal halide perovskites have shown chromogenic behavior whereby they can transform between two or more color states under the action of an external stimuli. The presence of a chromogenic mechanism in halide perovskites offers up the possibility of color-changing semiconductor devices, such as a dynamically color-changing solar cell.

In this work, we investigate explore the solvatochromism (color change in response to solvent intercalation-deintercalation) of 2D perovskite materials using methylamine. Methylamine demonstrates a rich intercalation chemistry with 2D halide perovskites, and the design of the long-chain cation plays a significant role in dictating the interactions. We demonstrate that methylamine can be retained in the film, leading to the formation of a variety of secondary phases, and that the A-site cation can be tuned to avoid methylamine retention and yield a more robust intercalation-deintercalation process. This is done by manipulating the organic-organic interactions as well as the interactions between both the organic cation head and tail with the inorganic metal halide layers. Several cation series are explored to adjust various aspects of the A-site cation interactions and provide experimental support for more general design rules around these different interactions. These initial experiments provide a framework for the design of solvatochromic halide perovskites and improve the understanding of 2D perovskite material design. Carefully tailoring the nature of the A-site cation will prove perhaps the key factor for the design of chromogenic halide perovskite semiconductors.