Water-Sensitive Mixed-Phase PEA₆SnI₈ Perovskite Derivative Single Crystal for Humidity Detection

Due to the sensitive photoelectric response upon an external humidity stimulus, metal halide perovskites have been demonstrated as emerging candidates for trace water detection. Here, we report an eco-friendly zero-dimensional PEA₆SnI₈ single crystal for efficient humidity detection, which can exhibit luminescent chromism with an instant trace water response as low as 0.02 ppm. The characterizations and spectroscopic measurements demontrated that the PEA₆SnI₈ single crystal has mixed phases with a triclinic phase in the surface and a hexagonal phase in the interior. By measuring the water-induced photoluminesence change during the transformation from triclinic PEA₆SnI₈ phase to PEA₂SnI₄, the environmental humidity can be determined. Furthermore, the as-formed PEA₂SnI₄ in the surface of the mixed-phase PEA₆SnI₈ crystal can be removed by dichloromethane (DCM) washing and the pristine mixed-phase crystallographic structure of PEA₆SnI₈ crystal can recover through a facile phase transformation. The rapid and reversible color change of a mixed-phase PEA₆SnI₈ crystal upon water and DCM process provides an advanced functional material for luminescent humidity sensors with an extremely low detection limit.