Polarization-resolved surface and bulk states in CsPbBr3 single crystals via second harmonic generation

Due to their superior electronic and optical properties, halide perovskite single crystals have been potential candidates for developing high-efficiency optoelectronic devices. Defect states located on the surface or within the bulk of single crystals play a crucial role in determining the performance of devices. In this work, the surface and bulk states in CsPbBr3 single crystals were investigated by polarization-resolved second harmonic generation (SHG) measurements. Onefold anisotropy of SHG intensity indicates that the polycrystalline Cs4PbBr6 and CsPb2Br5 phases dominate the surface, which exhibits Cs symmetry. Moreover, an unpolarized and strong luminescence was observed induced by two-photon absorption, which displays a twofold symmetry. Br vacancies within the bulk were identified as the radiative recombination centers according to their energy level position. These experimental results not only establish a method for distinguishing between surface and bulk states but also facilitate a deeper understanding of the optical properties of defect states in CsPbBr3 single crystals.