Structural Reconstruction in Lead-Free Two-Dimensional Tin Iodide Perovskites Leading to High Quantum Yield Emission

We report a structural reconstruction-induced high photoluminescence quantum yield of 25% in colloidal two-dimensional tin iodide nanosheets that are synthesized by a hot-injection method. The assynthesized red-colored nanosheets of octylammonium tin iodide perovskites at room temperature transform to white hexagonal nanosheets upon washing or exposure to light. This structural change increases the bandgap from 2.0 to 3.0 eV, inducing a large Stokes shift and a broadband emission. Further, a long photoluminescence lifetime of about 1 mu s is measured for the nanosheets. Such long-lived broad and intense photoluminescence with a large Stokes shift is anticipated to originate from tin iodide clusters that are formed during the structural reconstruction. The stereoactive 5s(2) lone pair of tin(II) ions perturbs the excited state geometry of the white hexagonal nanosheets and facilitates the formation of self-trapped excitons. Such broadband and intensely emitting metal halide nanosheets are promising for white light-emitting diodes.

Automated summary

We report a high photoluminescence quantum yield of 25% in colloidal two-dimensional tin iodide nanosheets that are synthesized by a hot-injection method, induced by structural reconstruction. The red-colored nanosheets transform to white hexagonal nanosheets upon washing or exposure to light, leading to an increase in bandgap and a large Stokes shift. The long photoluminescence lifetime is attributed to the formation of tin iodide clusters during the structural reconstruction. The stereoactive 5s(2) lone pair of tin(II) ions perturbs the excited state geometry of the nanosheets, facilitating the formation of self-trapped excitons. These broadband and intensely emitting metal halide nanosheets show promise for white light-emitting diodes.