Structural Reconstruction in Lead-free Two-dimensional Tin Iodide Perovskites Leading to High Quantum Yield Emission

TL;DR

This study demonstrates that structural reconstruction in lead-free two-dimensional tin iodide perovskites significantly enhances their photoluminescence quantum yield and emission properties, making them promising for white light-emitting applications.

Contribution

It reveals a novel structural transformation mechanism that boosts quantum yield and broadband emission in tin iodide nanosheets, a lead-free alternative for optoelectronic devices.

Findings

Quantum yield increased to 25% after structural change

Bandgap widened from 2.0 eV to 3.0 eV

Photoluminescence lifetime extended to about 1 microsecond

Abstract

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 as-synthesized 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 eV to 3.0 eV, inducing a large Stokes shift and a broadband emission. Further, a long photoluminescence lifetime of about 1 microsecond is measured for the nanosheets. Such long-lived broad and intense photoluminescence with large Stokes shift is anticipated to originate from tin iodide clusters that are formed during the structural reconstruction. Stereoactive 5s2 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.