(NH3(CH2)7NH3)2Sn3I10 a vacancy-ordered 3D tin(II) perovskite-derived semiconductor

Ordering vacancies in hybrid Sn(II) halide semiconductors provides a strategy for preventing uncontrolled oxidation and formation of mobile holes. In this study, we report the structure and optical and electronic properties of (NH3(CH2)7NH3)2Sn3I10, a vacancy-ordered perovskite derivative with three-dimensional inorganic connectivity. The crystal structure resembles that of a Dion-Jacobson layered perovskite derivative, but with [SnI5] square pyramids bridging the layers. UV-visible diffuse reflectance spectroscopy reveals a sharp onset of light absorption at 1.86(1) eV with the photoluminescence emission maximum at 1.90(1) eV. Yet, the maximum excitation occurring from 3.42 eV to 3.81 eV (325 nm to 370 nm), revealing a significant Stokes shift of 1.3 eV. The electronic properties determined from dark and time-resolved microwave conductivity measurements reveal a minimum carrier mobility of 4.3 x 10-2 cm2 V-1 s-1 and maximum carrier density of 5.96 x 1016 cm-3, a uniquely low value for a hybrid Sn(II) halide semiconductor. The transport behavior in combination with first principles calculations of the electronic band structure and dielectric permittivity suggest polaron-mediated electronic transport, yet the photogenerated carriers have a fast and fluence-dependent non-radiative recombination rate, suggestive of localized "defect-like" states at the band edge. The observed photoluminescence is most consistent with single-ion like behavior of an asymmetric Sn(II) environment. Together, these results suggest that defect ordering presents a strategy for the reduction of mobile charge carriers at equilibrium.