Spacer Switched Two Dimensional Tin Bromide Perovskites Leading to Ambient Stable Near Unity Photoluminescence Quantum Yield

Semiconductor nanostructures with near-unity photoluminescence quantum yields (PLQYs) are imperative for light-emitting diodes and display devices.A PLQY of 99.7±0.3% has been obtained by stabilizing 91% of the Sn2+ state in the Dion-Jacobson (8N8)SnBr4 (8N8-DJ) perovskite with 1,8 diaminooctane (8N8) interlayer spacer. The PLQY is favoredby a longerchain length of the hydrophobic spacer molecule, the extent of octahedral tilting and the preference of Sn2+at theB-site over Pb2+.The near-unity PLQY of 8N8-DJ has outstanding ambient stability under relative humidity (RH) of 55%for30 days throughout the entire excitation wavelength range, RH 75% for 3 days and 100°C for 3 h. By changing the spacer to n-octylamine (8N), Ruddlesden-Popper (8N)2SnBr4 (8N-RP) also has an appreciable PLQY of 91.7±0.6%, but having poor ambientstability due to increased lattice strain and structural degradation. The PL experiments from 5K to 300K decipher the room temperature PLQY to be due to the self-trapped excitons (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 also remains unchanged from its powder form to the polymer-embedded perovskite films.