Effects of Low-Temperature Annealing on CsPbBr3 Thin-Films by Ultrafast THz Spectroscopy

The high stability of the all-inorganic lead-halide perovskite CsPbBr3 in the humid environment makes it an attractive candidate for the development of photovoltaic applications. Nevertheless the efficiency of CsPbBr3 solar cells [1] is still not competitive with that of solar cells based on hybrid organic-inorganic or mixed-halide perovskites. We produced CsPbBr3 thin-films by vacuum thermal evaporation. We employed then THz spectroscopy to highlight the different behavior of the material annealed at 180◦C for 30 minutes, compared to the as-deposited one [2]. We completed our observations with optical absorption, photoluminescence (PL), X-ray diffraction (XRD), and scanning electron microscopy measurements (SEM). The SEM measurements confirmed the expected modification of the morphology of the thin-film, presenting an increased grain size after the annealing process. Nevertheless, our 400 nm pump-THz probe measurements unexpectedly revealed faster relaxation dynamics in the annealed sample compared to the as-deposited material.