Temperature-Dependent Recombination Dynamics of Photocarriers in CsPbBr₃ Microcrystals Revealed by Ultrafast Terahertz Spectroscopy

We study the ultrafast dynamics of photoexcited charge carriers in micron-scale crystals composed of the inorganic perovskite CsPbBr₃ with time-resolved terahertz spectroscopy. Exciting with photon energy close to the band edge, we find that a fast (< 10 ps) decay emerges in the terahertz photoconductivity with increasing pump fluence and decreasing temperature, dominating the dynamics at 4 K. The fluence-dependent dynamics can be globally fit by a nonlinear recombination model, which reveals that the primary nonlinear recombination mechanism depends on temperature, with Auger scattering determining the fast decay at 77 K but radiative recombination responsible for the fast decay at 4 K. Spectroscopically, the terahertz photoconductivity resembles a Drude response at all delays, yet an additional Lorentz component due to an above-bandwidth exciton resonance is needed to fully reproduce the data. The coexistence of excitons with free charge carriers impacts the scale of the recombination coefficients, as the absorbed photon density significantly exceeds the free charge carrier density.