Synthesis, Structure, Band Gap, and Near-Infrared Photosensitivity of a New Chalcogenide Crystal, (NH₄)₄Ag₁₂Sn₇Se₂₂

A new chalcogenide crystal, (NH4)4Ag12Sn7Se22 (FJSM-STS), has been solvothermally synthesized. The crystal structure, which is composed of arrays of [Sn3Se9]n6n− chains interconnecting [SnAg6Se10]n10n− and [Ag3Se4]n5n− layers, is unprecedented among the reported A/Ag/Sn/Q (A = cation; Q = S, Se, and Te) compounds. Optical absorption together with theoretical calculations of the band structure indicate a direct band gap of 1.21 eV for FJSM-STS, which is close to the ideal band gap to maximize the photoconversion efficiency proposed by Shockley and Queisser. The toxic-metal-free crystal of FJSM-STS exhibits obvious photosensitivity in the near-infrared range. The variates of power and temperature on the photosensitivity have been studied.