Correlating Rashba Suppression with Exciton Binding in Low-Dimensional Metal Halide Perovskites
Marco Antonio de Andrade Queiroz, Danilo Neves Silveira, Fernando P. Sabino, Carlos M. O. Bastos, Celso R. C. Rêgo, Maurício J. Piotrowski, Alexandre C. Dias, Diego Guedes-SobrinhoAbstract
We used DFT-1/2+SOC band structures mapped to Wannier tight-binding Hamiltonians and solved with the Bethe–Salpeter equation to examine how confinement, polymorphism, and metal off-centering tune excitons in Pb- and Sn-iodide perovskites in 3D (MA(Pb or Sn)I3), quasi-2D (BA2(PborSn)I4), and model quasi-1D (BA3(PborSn)I5). The 3D polymorphs show a clear trend: as symmetry increases from orthorhombic to tetragonal to pseudocubic, Eb decreases. At fixed dimensionality, restoring local metal-centered symmetry suppresses Rashba splitting. It reduces or preserves Eb, indicating that SOC affects excitons mainly through band-edge structure rather than direct strengthening of the electron–hole Coulomb kernel. Low-dimensional compounds retain much larger Eb than 3D analogs, although quasi-1D is not monotonic with quasi-2D. Photoluminescence spectra place the lowest excitons at the optical gap, consistent with bright ground-state excitons.