Photo-excited carrier behaviors of two-dimensional tin halide perovskite single crystals

Two-dimensional (2D) tin halide perovskites have attracted significant interest due to their exceptional optoelectronic properties, high carrier mobility, and low toxicity. However, a fundamental understanding of the correlation between the structure and the photo-excited carriers' behavior remains ambiguous. Herein, we synthesize (PEA)2MAn−1SnnI3n+1 (n = 1–4) single crystals with tunable quantum-well thickness (n value). The structure distortion and optoelectronic properties are influenced by the n value. Our density functional theory calculations reveal that the energy band gap and carrier lifetime are closely related to the n value due to the quantum confinement and dielectric screening. Remarkably, unlike lead halide perovskites, 2D tin halide perovskites consistently exhibit excitons as the dominant photo-excited carriers, irrespective of the n values. These findings offer critical insights into designing and fabricating high-performance optoelectronic devices based on 2D tin halide perovskites, particularly in terms of tuning their properties through n values.