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Unveiling the Photo- and Thermal-Stability of Cesium Lead Halide Perovskite Nanocrystals.

Lead halide perovskites possess unique characteristics well-suited for optoelectronic and energy capture devices, however, concerns about their long-term stability remain. All-inorganic CsPbX3 (X = Cl, Br, I) perovskite nanocrystals have been reported with improved stability. We investigate the photo- and thermal-stability properties of CsPbX3 (X = Cl, Br, I) nanocrystals by electron microscopy, x-ray diffraction, thermogravimetric analysis, ensemble and single particle spectral characterization. CsPbBr¬3 is stable under 1-sun illumination for 16 h in ambient conditions, although single crystal analysis indicates the luminescence states change over time. CsPbBr¬3 is also stable to heating to 250 °C. Large CsPbI3 crystals (34 ± 5 nm) are the least stable under the same conditions; and with heating, the γ (black) phase reverts to the non-luminescent δ phase. Smaller CsPbI3 nanocrystals (14 ± 2 nm) purified by a different washing strategy exhibit improved photostability with no evidence of crystal growth but are still thermally unstable. Both CsPbCl3 and CsPbBr3 show crystal growth under irradiation or heat, likely with a preferential orientation. TGA-FTIR reveals nanocrystal mass loss was only from liberation and subsequent degradation of surface ligands. Encapsulation or other protective strategies should be employed for long-term stability under conditions of high irradiance or temperature.