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% Sn 2+ in the Dion–Jacobson (8N8)SnBr 4 (8N8-DJ) perovskite with 1,8-diaminooctane (8N8) spacer. The PLQY is favored by a longer spacer molecule and out-of-plane octahedral tilting. The PLQY shows one-month ambient stability under high relative humidity (RH) and temperature. With n -octylamine (8N) spacer, Ruddlesden–Popper (8N) 2 SnBr 4 (8N-RP) also shows PLQY of 91.7 ± 0.6%, but it has poor ambient stability. The 5–300 K PL experiments decipher the self-trapped excitons (STEs) where the self-trapping depth is 25.6 ± 0.4 meV below the conduction band because of strong carrier–phonon coupling. The microsecond long-lived STE 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 SnBr 6 4– octahedra and 8N8 spacer, leading to a rigid structure.