Abstract
Two-dimensional (2D) organic-inorganic lead halide perovskites possess strong spin-orbit coupling, and in the presence of broken inversion symmetry, this may lead to helical excitons and Rashba splitting at the band extrema1-6. However, a direct and systematic measurement of the helical excitons and the Rashba parameter in the system is still lacking. Here, we report distinct two bright co-helical and two dark anti-helical excitons in single crystal ((CH3(CH2)3NH3)2(CH3NH3)n-1PbnI3n+1 (n = 1 to 4), where n determines quantum well (QW) thickness of inorganic layer7. By comprehensively analyzing the fine structure of helical excitons, we find that the Rashba splitting originates from surface inversion asymmetry and surface-normal electric fields, which are determined by the QW’s dielectric environment, n and temperature. The Rashba splitting parameter is found among the highest recorded of 2.66 and 2.5 eV∙Å for the conduction and valence band of n=1 Iodide, respectively, and reduces for n>1 Iodide. Our result shows the importance of helical excitons and Rashba splitting and presents a direct method to quantify the Rashba parameter in complex halide perovskites. We hope that our study inspires applications of QW materials in novel spintronic devices.
Solution‐Processed Faraday Rotators Using Single Crystal Lead Halide Perovskites
