Abstract
We report the preparation of monolayer (n = 1), few-layer (n = 2–5) and 3D (n = ∞) organic lead bromide perovskite nanoplatelets (NPLs) by tuning the molar ratio of methylammonium bromide (MABr) and hexadecammonium bromide (HABr). The absorption spectrum of the monolayer (HA)2PbBr4 perovskite NPLs shows about 138 nm blue shift from that of 3D MAPbBr3 perovskites, which is attributed to strong quantum confinement effect. We further investigate the two-photon photoluminescence (PL) of the NPLs and measure the exciton binding energy of monolayer perovskite NPLs using linear absorption and two-photon PL excitation spectroscopy. The exciton binding energy of monolayer perovskite NPLs is about 218 meV, which is far larger than tens of meV in 3D lead halide perovskites.
Highlights
The exciton binding energy of monolayer perovskite NPLs is 218 meV, which is far larger than tens of meV in 3D counterparts
Layered 2D perovskite NPLs are described by the general formula (R)2[ABX3]n-1BX4,24 where R, A, B and X are a long-chain alkylammonium ligand (HA), organic molecular cation (MA), divalent metal cation (Pb2+), halide anion, respectively
The rounded corners are observed from Transmission Electron Microscope (TEM) images (Fig. S2c and S2d of the supplementary material) of perovskite NPLs with methylammonium bromide (MABr):hexadecammonium bromide (HABr) = 2:8
Summary
Recent outstanding progresses in solar cells and light-emitting diode applications have exhibited promising optoelectronic properties of organic-inorganic lead halide perovskites.[1,2,3,4,5,6,7,8,9] These perovskites (such as MAPbX3, FAPbX3, CsPbX3, X = Cl, Br, I) exhibit a large absorption coefficient, high charge carrier mobility, small exciton binding energy, as well as long charge diffusion length.[10,11,12] Their absorption and photoluminescence (PL) wavelength can be tuned from visible to near infrared through substituting cationic or anionic components.[13,14,15,16,17,18]. The optical and excitonic properties of perovskites are dependent on the chemical component, and crystal structure.[19,20,21,22,23] Perovskite nanoplatelets (NPLs) have attracted extensive attention due to their unique optical properties.[24,25,26,27,28,29] Mechanical exfoliation, vapor transport chemical deposition method, ligand-assisted exfoliation, and dilution-induced approach have been reported to prepare perovskite NPLs.[24,25,26,27] The morphology and optical properties of perovskite NPLs are different from 3D counterparts due to the quantum confinement effect, which is observed when the crystal size becomes comparable to or smaller than the exciton Bohr radius in the perovskite materials.[20,28] Sichert et al
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