Temperature-Dependent Exciton Dynamics of Cs ₄ CuSb ₂ Cl ₁₂ Layered Double Perovskite Nanocrystal Thin Films

Cs₄CuSb₂Cl₁₂ layered double perovskite nanocrystals were synthesized via a hot injection method and cast into thin films. Their crystal structure and particle morphology were determined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). UV-vis electronic absorption spectra show a high-energy band (HEB) peaking at 541 nm (2.29 eV) and a low-energy band (LEB) appearing as a shoulder at 649 nm (1.91 eV) at room temperature (RT). At 77 K, the peak of the HEB red shifts to 561 nm (2.21 eV) while the LEB is enhanced and red shifts to 692 nm (1.79 eV). Temperature-dependent femtosecond transient absorption spectroscopy (TAS) was utilized to probe the exciton dynamics of the nanocrystal films and reveals several dynamic processes attributed to hot electron cooling, relaxation into triplet states, and electron-hole recombination. A detailed kinetic model was proposed to simulate these processes and gain deeper insight into temperature-dependent exciton dynamics.