Functionalized hybrid perovskite nanocrystals with organic ligands showing a stable 3D/2D core/shell structure for display and laser applications

A simple one-pot synthesis of stable red-emitting perovskite nanocrystals (PeNCs) involved the addition of Cs-oleate, formamidinium bromide (FABr) and organic ammonium iodide salts (represented as LnI,n= 1-5) to a hot flask containing oleic acid (OA), oleylamine (OLA) and PbI₂. The crystal structures of these PeNCs that are rich in halide on the surface enable surface-defect passivation, whereas they conform to structural formula Cs_1−xFA_xPbBr_yI_3−yin the bulk. The photoluminescence (PL) spectrum ofL0in the absence of LnI salts displays an orange colour at 589 nm, whereas those ofL1-L5show red spectral shifts toward 622-629 nm in octane solutions. The PL decay profiles of these PeNCs (L0-L5) were fitted with a stretched-exponential function with lifetimes in the range of 11.1 (L0)-15.8 ns (L3) and with PL quantum yields 69 (L5)-79% (L1); the values of dispersion factorβare in the range of 0.91-0.94, indicating the diminished surface defects because of the rich halides on the surface. Upon storage of these thin-film samples in an ambient air environment with RH ∼30%, the 3D/2D core-shell structure formed forL1-L5exhibited spectral shifts from ∼640 nm toward smaller wavelengths. The PeNC film with a 4-trifluoromethyl-benzylammonium protection ligand (L5) exhibited a remarkable enduring stability with stabilized emission at 630 nm, which is suitable for display applications to serve as a red QD source. Using the femtosecond transient absorption spectral technique, we observed great optical gains for theL5/ethyl cellulose film, suitable for laser applications.