Weak dispersion of exciton Land\'e factor with band gap energy in lead halide perovskites: Approximate compensation of the electron and hole dependences

TL;DR

This study measures the exciton Landé g-factor in various lead halide perovskites, revealing its near constancy across different band gaps due to electron and hole g-factor compensation, enhancing understanding of their fundamental properties.

Contribution

It provides the first comprehensive measurement of exciton g-factors across a wide range of lead halide perovskites and demonstrates their near invariance with band gap energy.

Findings

Exciton g-factors range from +2.3 to +2.7 across materials.

Electron and hole g-factors roughly compensate, leading to a nearly isotropic exciton g-factor.

Experimental results agree well with theoretical models.

Abstract

The photovoltaic and optoelectronic properties of lead halide perovskite semiconductors are controlled by excitons, so that investigation of their fundamental properties is of critical importance. The exciton Land\'e or g-factor g_X is the key parameter, determining the exciton Zeeman spin splitting in magnetic fields. The exciton, electron and hole carrier g-factors provide information on the band structure, including its anisotropy, and the parameters contributing to the electron and hole effective masses. We measure g_X by reflectivity in magnetic fields up to 60 T for lead halide perovskite crystals. The materials band gap energies at a liquid helium temperature vary widely across the visible spectral range from 1.520 up to 3.213 eV in hybrid organic-inorganic and fully inorganic perovskites with different cations and halogens: FA_{0.9}Cs_{0.1}PbI_{2.8}Br_{0.2], MAPbI_{3}, FAPbBr_{3}, CsPbBr_{3}, and MAPb(Br_{0.05}Cl_{0.95})_{3}. We find the exciton g-factors to be nearly constant, ranging from +2.3 to +2.7. Thus, the strong dependences of the electron and hole g-factors on the band gap roughly compensate each other when combining to the exciton g-factor. The same is true for the anisotropies of the carrier g-factors, resulting in a nearly isotropic exciton g-factor. The experimental data are compared favorably with model calculation results.