Spin dynamics of excitons and carriers in mixed-cation MA$_{x}$FA$_{1-x}$PbI$_{3}$ perovskite crystals: alloy fluctuations probed by optical orientation

TL;DR

This study investigates how alloy fluctuations affect spin dynamics of excitons and carriers in mixed-cation perovskite crystals using optical orientation, revealing disorder-induced scattering impacts and consistent g-factor trends.

Contribution

It provides experimental insights into the influence of alloy fluctuations on spin dynamics and optical orientation in mixed-cation perovskites, extending understanding of disorder effects.

Findings

High exciton optical orientation in low and high alloy compositions

Reduced optical orientation at intermediate alloy composition due to disorder

Electron and hole g-factors follow universal trend with band gap energy

Abstract

Optical spin orientation measured by time-resolved photoluminescence provides a powerful tool to probe the spin dynamics of excitons and charge carriers in perovskite semiconductors. The impact of alloy fluctuations on the spin dynamics of mixed-cation \MAFAPI{} perovskite single crystals is studied here experimentally. The optical orientation is measured under nonresonant excitation for crystals with $x = 0.1$, $0.4$, and $0.8$ at cryogenic temperatures and compared with data on \MAPI{} crystals. The high degree of exciton optical orientation of $75-80$\% for $x = 0.1$ and $0.8$ reduces to about 60\% for $x = 0.4$. A similar trend is observed for the carrier spin optical orientation. This behavior is attributed to enhanced scattering of free excitons and carriers in the alloys with increased compositional and structural disorder. From the Larmor spin precession measured from spin dynamics in an external magnetic field applied in the Voigt geometry, the electron and hole $g$-factors are evaluated. Their dependence on the band gap energy in \MAFAPI{} crystals follows the universal trend previously established for lead halide perovskites.