Ultrafast Carrier Dynamics in CH₃NH₃PbBr₃ Perovskite Single-Crystal Thin Films

Single-crystal (SC) perovskites have emerged as promising contenders for perovskite solar cells (PSCs) and the next generation of optoelectronic devices. Compared to polycrystalline (PLC) perovskites, SC perovskites have reduced trap densities, enhanced carrier mobility, and extended carrier lifetime. However, a comprehensive understanding of carrier dynamics in perovskite SCs is still lacking, primarily due to their bulk dimensions, which are not suitable for ultrafast spectroscopic studies. Here, we prepared spectroscopically thin SC films for investigating their ultrafast photophysical properties. It is found that the excitation above the band gap results in the quasi-thermalization of carrier distributions within 100 fs, with an initial carrier temperature of the SC film three times higher than that of the PLC film. Our results indicate that the contribution of inelastic carrier–carrier scattering in the SC film is significantly lower than that in the PLC film. During carrier cooling, a short-lived sub-band gap transient absorption signal arises only in the SC film, which can be explained by the interplay of band gap renormalization and hot-carrier distributions. However, it is absent in the PLC film until the excitation density surpasses the amplified spontaneous emission threshold. Furthermore, cooling of hot carriers in the SC film is accelerated by a stronger interaction between the photocarrier and the lattice.