Temperature Dependence of Photoinduced Carrier Spin Relaxation Dynamics in CsPbBr₃ and MAPbBr₃ Perovskite Quantum Dots

Temperature dependent carrier spin relaxation dynamics of CH₃NH₃PbBr₃ (MAPbBr₃) and CsPbBr₃ perovskite quantum dots (PQDs) have been studied at room temperature (RT), 150 K, and 77 K using spin selective femtosecond transient absorption (fs-TA) spectroscopy. Results reveal minimal temperature dependence in the MAPbBr₃ PQDs with a lifetime of 2.2 ps. In contrast, the CsPbBr₃ PQDs show strong temperature dependence, with the carrier spin lifetime increasing from RT (2.0 ps) to 150 K (11 ps) and to 77 K (57 ps). This behavior suggests the two PQD systems exhibit different carrier spin relaxation mechanisms. The dominant mechanism in CsPbBr₃ PQDs is attributed to the Eliot-Yafet (EY) mechanism, modulated primarily by an electron-phonon interaction that is reduced at cryogenic temperatures. In contrast, for the MAPbBr₃ PQDs the D'yakonov-Perel (DP) mechanism is dominant, likely due to broken inversion symmetry associated with the presence of MA, which induces a dynamical Rashba effect at finite temperature.