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.