Crystal Structure, Band Gap, and Optoelectronic Performance of Lead‐Free Cs₂FeCl₅⋅H₂O Erythrosiderite‐Halide Single Crystal and Its Thin Film

Abstract The unique physical and chemical properties of erythrosiderite‐halides make them candidates for semiconductor materials and optoelectronic devices. However, research on the optoelectronic properties of these materials is still relatively limited. This study presents the crystal structure and optoelectronic properties of Cs₂FeCl₅⋅H₂O erythrosiderite halide. The results show that Cs₂FeCl₅⋅H₂O is an orange‐red needle‐like crystal, with its crystal system and space group belonging to the orthorhombic system and Cmcm(63), respectively. Photodetectors made from Cs₂FeCl₅⋅H₂O exhibit stable photocurrent responses in the visible light range (from 397 to 564 nm). Under conditions of a light intensity of 30 W/m 2 at 397 nm with a bias voltage of 4.5 V, the responsivity of Cs₂FeCl₅⋅H₂O is 8.41 mA/W, and the detectivity is 4.43 × 10 6 Jones. There is a strong linear relationship between the net photocurrent density of Cs₂FeCl₅⋅H₂O and light intensity, as well as a strong linear relationship between responsivity and voltage, with R 2 =0.96. Thus, Cs₂FeCl₅⋅H₂O has excellent optoelectronic performance and is a promising compound for optoelectronic applications.