Linear Optical Properties of Two-Dimensional (Benzylammonium)₂PbBr₄ Perovskites

Two-dimensional organometallic perovskites are promising materials for nonlinear optics, photonics, and optoelectronics due to their strong excitonic effects, quantum confinement, and structural tunability. We investigate the electronic and optical properties of bulk and few-layered (Benzylammonium)₂PbBr₄ organometallic perovskite. The bulk crystals were exfoliated into few-layered nanosheets and characterized using X-ray diffraction and energy-dispersive X-ray spectroscopy/scanning electron microscopy. Optical imaging confirmed the exfoliated layers. Electronic band structure calculation using the first-principles density functional theory finds the band gap of ~2.7 eV, consistent with experimental values, and identifies the presence of optically inactive surface states in few-layer slabs. These states are attributed to surface C-atoms p-orbitals, which are separated by a large distance (>10 Å) in real space and do not overlap with Pb-s/p states forming the valence bands, resulting in the absence of an optical signal in the linear regime.