(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 connectiv- ity. The unit cell is a 4x4 x2 supercell of the cubic perovskite aristotype with a 1 small monoclinic shear (beta ~ 91°); thus single crystals remain heavily twinned. There- fore, the structure determination requires combination of synchrotron X-ray powder and single-crystal X-ray diffraction methods. The crystal structure resembles that of a Dion-Jacobsen layered perovskite derivative, but with [SnI5] square pyramids bridging the layers. UV-visible diffuse reflectance spectroscopy reveals a sharp onset of light ab- sorption at 1.86(1) eV. Photoluminescence emission-excitation mapping indicates an emission peak at 1.90(1) eV, with 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. Thus, the photo- luminescence excitation spectra are significant blue shifted from the absorption spec- trum. The electronic properties determined from dark and time-resolved microwave conductivity measurements reveal a minimum carrier mobility of 4.3 x10^12 cm2/V/s and maximum carrier density of 5.96x10^16 cm^3, a uniquely low value for a hybrid Sn(II) halide semiconductor. The transport behavior in combination with first principles calculations (HSE06 with spin orbit coupling) of the electronic band struc- ture and dielectric permittivity suggest polaron-mediated electronic transport, yet the photogenerated carriers have a fast and fluence-dependent non-radiative recombina- tion 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 presentation of mobile charge carriers at equilibrium, but with a con- sequence of electronic relaxation resembling that of a highly defected semiconductor.