Ambient-stable near Unity Photoluminescence Quantum Yield in Two-dimensional Tin Bromide Perovskites

Semiconductor nanostructures with near-unity photoluminescence quantum yields (PLQYs) are imperative for light-emitting diodes and display devices.With 1,8 diaminooctane (8N8) interlayer spacer, the Dion-Jacobson (8N8)SnBr4 (8N8-DJ) perovskite demonstrates a PLQY of 99.7±0.3%. The near-unity PLQY of 8N8-DJ has outstanding ambient stability for over a month throughout the entire excitation wavelength range. By changing the spacer to n-octylamine (8N), Ruddlesden-Popper (8N)2SnBr4 (8N-RP) also has an appreciable PLQY of 91.7±0.6%. However, the PLQY of 8N-RP is unstable under ambient conditions due to increased lattice strain and structural degradation of the perovskite phase. The PL experiments from 5K to 300K decipher the room temperature PLQY to be due to the self-trapped emission (STE) where the self-trapping depth is 25.6±0.4 meV below the conduction band as a result of strong carrier-phonon coupling. With 34.7-37.3meV exciton binding energy, the ~5.5 s long-lived STE emission dominates over the band edge (BE) peaks at lower excitation wavelengths and higher temperatures. The higher PLQY and stability of 8N8-DJ are due to the stronger interaction between SnBr64- octahedra and 1,8 diammonium octane cation leading to a more rigid structure. The near-unity PLQY of 8N8-DJ remains unchanged from its powder form to the polymer-embedded perovskite films with varying thicknesses.