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% Sn2+ in the Dion–Jacobson (8N8)­SnBr4 (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)2SnBr4 (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 SnBr6 4– octahedra and 8N8 spacer, leading to a rigid structure.

Lead-free layered double perovskite nanocrystals (NCs) with tunable visible range emission, high carrier mobility and low trap density are the need of the hour to make them applicable for optoelectronic and photovoltaic devices. Introduction of Cu2+ in the high band gap Cs3Sb2Cl9 lattice transforms it to the monoclinic Cs4CuSb2Cl12 (CCSC) NCs having a direct band gap of 1.96 eV. The replacement of 50% Cl− by I− ions generates <5 nm Cs4CuSb2Cl6I6 (C6I6) monodispersed NCs with an unchanged crystal system but with further lowering of the band gap to 1.92 eV. The p-type C6I6 NCs exhibit emission spectra, lower trap density, appreciable hole mobility and most importantly a lower exciton binding energy of only 50.8 ± 1.3 meV. The temperature dependent photoluminescence (PL) spectra of the C6I6 NCs show a decrease in non-radiative recombination from 300 K down to 78 K. When applied as the photoactive layer in out-of-plane photodetector devices, C6I6 NC devices exhibit an appreciable responsivity of 0.67 A W−1 at 5 V, detectivity of 4.55 × 108 Jones (2.5 V), and fast photoresponse with rise and fall time of 126 and 94 ms, respectively. On the other hand, higher I- substitution in Cs4CuSb2Cl2I10 NCs (C2I10) degrades the lattice into a mixture of monoclinic and trigonal crystal phases, which also lowers the device performance.

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.

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.