Lead-free defective halide perovskites Cs2SnX6 (X = Cl, Br, I) for highly robust formaldehyde sensing at room temperature

In this contribution, all-inorganic lead-free halide perovskites Cs2SnX6 (X = Cl, Br, I) were synthesized by simple room-temperature precipitation. Material characterization demonstrated their feature in rich defects of halogen vacancies. As room-temperature formaldehyde (HCHO) sensing materials, Cs2SnX6 exhibited reliable sensitivity order of Cs2SnCl6 < Cs2SnBr6 < Cs2SnI6. Notably, the Cs2SnI6 sensor showed excellent selectivity for HCHO at room temperature with high response (Sr = 78, 100 ppm), short response/recovery time (3.6 s/7.2 s), good repeatability and long-term stability. Finally, the HCHO sensing mechanism was investigated via in-situ infrared analysis, conforming abundant intermediates of dioxymethylene, formate, and carbonate. The excellent sensing performance is attributed to rich iodine vacancies (VI) as active sites induced boosted stepwise oxidation of HCHO molecules on Cs2SnI6 surface. This work provides a fine candidate for practical HCHO detection at room temperature, and furthermore, gives new insights in designing halide perovskites for next-generation sensory devices.