TlSn₂I₅, a Robust Halide Antiperovskite Semiconductor for γ-Ray Detection at Room Temperature

The semiconductor TlSn₂I₅ with a two-dimensional crystal structure and an antiperovskite topology is a promising novel detection material. The compound crystallizes in the I4/mcm space group, has an indirect band gap of 2.14 eV, and melts congruently at 314 °C. Electronic band structure calculations reveal that the most facile electron transport is along the ab layered plane. Compared to CH₃NH₃PbX₃ (X = Br, I), TlSn₂I₅ features higher long-term stability, higher photon stopping power (average atomic number of 55), higher resistivity (∼10¹⁰ ω·cm), and robust mechanical properties. Centimeter-size TlSn₂I₅ single crystals grown from the melt by the Bridgman method can be used to fabricate detector devices, which detect Ag Kα X-rays (22 keV), ⁵⁷Co γ-rays (122 keV), and ²⁴¹Am α-particles (5.5 MeV). The mobility-lifetime product and mobility for electrons were estimated to be 1.1 × 10^-3 cm²·V^-1 and 94 ± 16 cm²·V^-1·s^-1, respectively. Unlike other halide perovskites, TlSn₂I₅ shows no signs of ionic polarization under long-term, high-voltage bias.