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

Abstract

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−y in the bulk. The photoluminescence (PL) spectrum of L0 in the absence of LnI salts displays an orange colour at 589 nm, whereas those of L1–L5 show 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 factor β are 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 for L1–L5 exhibited 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 the L5/ethyl cellulose film, suitable for laser applications.