Circular Dichroism Engineering via Bismuth Doping and Cation Substitution in 2D Lead-Halide Perovskites

Hybrid lead halide perovskites are renowned for their exceptional semiconductor properties, with tunable features such as crystal structure and electronic band gap due to the flexibility of their building blocks. By incorporating chiral organic cations, these materials can exhibit unique chiral properties like circularly polarized luminescence (CPL), chirality-induced spin selectivity, and spin-polarized electron currents. This makes them promising candidates for applications in circularly polarized light emitters, detectors, and spin filters in spintronics and quantum information technologies. Despite this potential, the mechanism of chirality transfer remains unclear due to complex structure-property relationships.

In this study, we explore the effects of heterovalent Bi³⁺ doping on the genuine circular dichroism (CD) in two families of 2D lead iodide perovskites featuring methylbenzylamine (MBA) and (pyridyl)ethylamine (PyEA) as organic cations. We observe successful chirality transfer from the organic cation to the perovskite in both materials, though with varying degrees. While the dissymmetry factor of (MBA)₂-PbI₄ aligns with literature values, PyEA-PbI₄ exhibits a notably higher dissymmetry factor, on the order of 10⁻². While the band gap remains constant upon Bi³⁺ substitution for Pb²⁺, the CD decreases with increasing Bi content, indicating that doping influences the chirality transfer. Interestingly, the electrical conductivity increases with Bi doping, highlighting its potential to enhance charge transport in these materials.

These results shed light on how structural factors modulate CD in hybrid perovskites, offering valuable insights for designing next generation chiroptical materials with improved efficiency and performance.