Reversible “on–off” conversion and ultra-high temperature sensitivity of a zero-dimensional lead-free Cs 2 InBr 5 (H 2 O):Sb 3+ perovskite

Zero-dimensional (0D) lead-free perovskites have garnered significant attention due to their unique optoelectronic properties and non-toxicity. However, the single response to stimuli in lead-free perovskites limits the versatility of multifunctional compounds. In this study, we abandoned the toxic bromic acid and utilized water as the reaction medium, to achieve an environmentally friendly green chemical route. We successfully prepared a zero-dimensional lead-free halide Cs 2 In 1− x Sb x Br 5 (H 2 O) perovskite with a fractal structure using an in situ solution crystallization method. Herein, we discovered that the recrystallization occurred beneath the smooth-grown rhombic crystal surface, forming fractal branched crystals. Interestingly, reversible luminescence color transitions from orange-red to yellow and return to the initial state were achieved in response to the individual stimuli of temperature and humidity. We found that H 2 O molecules played a crucial role in the color tuning, enabling reversible “on–off” switching modes with rapid modulation rates. Moreover, the 0D lead-free halide perovskite Cs 2 InBr 5 (H 2 O):Sb 3+ also exhibited excellent temperature sensitivity, with the relative sensitivity ( S R ) reaching up to 9.39% K −1 . This study provides valuable insights for the further development of halide perovskites in design and application fields, laying a foundation for the development of multifunctional smart materials and temperature sensing applications.