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\nyield of 25% in colloidal two-dimensional tin iodide nanosheets that are\nsynthesized by a hot-injection method. The as-synthesized red-colored\nnanosheets of octylammonium tin iodide perovskites at room temperature\ntransform to white hexagonal nanosheets upon washing or exposure to light. This\nstructural change increases the bandgap from 2.0 eV to 3.0 eV, inducing a large\nStokes shift and a broadband emission. Further, a long photoluminescence\nlifetime of about 1 microsecond is measured for the nanosheets. Such long-lived\nbroad and intense photoluminescence with large Stokes shift is anticipated to\noriginate from tin iodide clusters that are formed during the structural\nreconstruction. Stereoactive 5s2 lone pair of tin (II) ions perturbs the\nexcited state geometry of the white hexagonal nanosheets and facilitates the\nformation of self-trapped excitons. Such broadband and intensely emitting metal\nhalide nanosheets are promising for white light-emitting diodes.\n