Quantum confinement effect and exciton binding energy of layered perovskite nanoplatelets

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.