Integration of Photo‐ and Thermal‐Detection Based on Hexagonal Chalcogenide Perovskite Sr ₈ Ti ₇ S ₂₁ with Full Spectrum Absorption

Abstract Chalcogenide perovskites, such as BaZrS 3 , with a distorted 3D orthorhombic structure, have been extensively studied as absorber materials in solar cells due to their strong thermal stability, excellent electrical transport properties, and high absorption. However, the relatively high bandgap of orthorhombic chalcogenide perovskites limits their application in the near‐infrared region. In this work, it is demonstrated that Sr 8 Ti 7 S 21 , a chalcogenide perovskite with a quasi‐1D hexagonal structure, exhibits a significantly lower bandgap and a broader absorption spectrum extending into the infrared region. Sr 8 Ti 7 S 21 in various forms are synthesized, including powder, bulk, thick, and thin film. Using these materials, a thermistor and a photo‐thermoelectric generator is fabricated. The thermistor exhibits a B 30/90 value of 2400 K, comparable to commercial negative temperature coefficient (NTC) thermistors. The photo‐thermoelectric generator efficiently absorbs both visible and near‐infrared light, making it suitable for operation under natural sunlight. Additionally, a fire alarm system based on the photo‐thermal sensing capabilities of Sr 8 Ti 7 S 21 is developed. The characterization and diverse applications of Sr 8 Ti 7 S 21 presented in this work highlight the potential of low‐dimensional chalcogenide perovskites for use in photo‐ and thermal‐detection devices.