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

Abstract

Abstract Lead halide perovskites possess unique characteristics that are well‐suited for optoelectronic and energy capture devices, however, concerns about their long‐term stability remain. Limited stability is often linked to the methylammonium cation, and all‐inorganic CsPbX 3 (X=Cl, Br, I) perovskite nanocrystals have been reported with improved stability. In this work, the photostability and thermal stability properties of CsPbX 3 (X=Cl, Br, I) nanocrystals were investigated by means of electron microscopy, X‐ray diffraction, thermogravimetric analysis coupled with FTIR (TGA‐FTIR), ensemble and single particle spectral characterization. CsPbBr 3 was found to be stable under 1‐sun illumination for 16 h in ambient conditions, although single crystal luminescence analysis after illumination using a solar simulator indicates that the luminescence states are changing over time. CsPbBr 3 was also stable to heating to 250 °C. Large CsPbI 3 crystals (34±5 nm) were shown to be the least stable composition under the same conditions as both XRD reflections and Raman bands diminish under irradiation; and with heating the γ (black) phase reverts to the non‐luminescent δ phase. Smaller CsPbI 3 nanocrystals (14±2 nm) purified by a different washing strategy exhibited improved photostability with no evidence of crystal growth but were still thermally unstable. Both CsPbCl 3 and CsPbBr 3 show crystal growth under irradiation or heat, likely with a preferential orientation based on XRD patterns. TGA‐FTIR revealed 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 of these materials under conditions of high irradiance or temperature.