3D Chiral Metal Halide Semiconductors

Abstract

Chiral metal halides are promising materials for nonlinear optics and spin-selective devices. Typically, chirality is introduced via large chiral organic cations, leading to low-dimensional structures and limitations in charge transport. Here, we design a family of chiral metal halides based on the relatively small ditopic R/S-3-aminoquinuclidine (3-AQ) cation, forming an (R/S-3AQ)-Pb₂Br₆ structure closely related to the 3D corner-sharing octahedral network of perovskites. The resulting material exhibits a direct bandgap, isotropic band structure, and fully 3D photoexcitation. Circular dichroism confirms a chiral anisotropy factor consistent with theoretical predictions. Moreover, the material displays a Rashba effect in the conduction band, which is attributed to spin-orbit coupling and the lack of inversion symmetry. Offering rich chemical tunability and efficient 3D charge transport, this new class of chiral semiconductors provides a promising platform for advancing nonlinear optoelectronic and spintronic devices.

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(a) Chemical formula of 3-aminoquinuclidine (3-AQ). The asterisk marks the chiral center. (b–d) Sketches of the crystal structures of (R/S-3-AQ)­Pb₂Br₆ along the a, c, and b axes, respectively. The two crystallographically independent Pb ions are represented with their coordination octahedra in dark green (Pb1) and light green (Pb2), respectively. (e) Highlight of the (R-3-AQ)­Pb₂Br₆ N–H···Br hydrogen bonds interactions, represented as blue dashed lines.

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(a, c) Electronic band structures and projected density of states (PDOS) for the 3D and 2D materials, respectively. The PDOS was computed using the HSE06-SOC level of theory, whereas the band structures were initially obtained with PBE-SOC and subsequently corrected to align with the HSE06-SOC band gap. The insets in the PDOS panels illustrate the corresponding Brillouin zone representations. (b, d) Rashba splitting of the valence and conduction bands for the respective materials, highlighting spin–orbit coupling effects. The energy zero reference is set to the valence band maximum (VBM) and conduction band minimum (CBM) to enhance the visualization of the splitting.

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Tauc plot for (a) (R/S-3AQ)­Pb₂Br₆ and (b) (R/S-3-AQ)₂PbBr₄·2Br at 300 K; CD spectra for (c) (R/S-3AQ)­Pb₂Br₆ and (d) (R/S-3-AQ)₂PbBr₄·2Br.