Metal halide perovskites are promising candidates in the field of photocatalytic activity, photovoltaics (PV), light-emitting applications, and lasers due to their versatile composition, crystalline structure, and tunable optical properties. Generally, the metal halide perovskites (HPs) are expressed in the form of ABX3, where A is a monovalent cation (organic or inorganic), B is a divalent cation (Pb 2+ , Sn 2+ , Ge 2+ ), and X is the halide anion (Cl¯, Br¯, or I¯). The dimensionality of the perovskite crystalline structure is defined by the connectivity of BX6 4- octahedra (corners-sharing) and classified from zero to three-dimension (0D-3D), where ABX3 is 3D, and A4BX6 is the 0D. This variation in the crystalline structure significantly affects the optical properties of the perovskite materials. For instance, the band gap value of the 3D CsPbBr3 is about 2.35 eV, and that of 0D C4PbBr6 is 3.90 eV. Also, while the 3D CsPbBr3 possesses a bright green photoluminescent (PL) emission (~ 527 nm), the PL emission from the 0D Cs4PbBr6 is debatable. Some studies state that the green emission from the 0D C4PbBr6 is an inherent property of the materials, whereas others attribute this emission to the contamination by the 3D CsPbBr3 phase and structural defects. Since the halide perovskite-nanocrystals (HP-NCs) have highly active sites, it is favorable for carrying out photocatalytic reactions. However, the stability of HP-NCs is affected by the solvent, surface ligands, and environmental conditions. Numerous studies show HP-NC's sensitivity to oxygen and moisture and that they decompose upon illumination. Various techniques are used to study the decomposition process of HP-NCs. The most common methods are the in-situ PL and absorbance measurements, where quenching of the spectral features is indicative of the decomposition progress. Another technique is calorimetry, where the enthalpy of the dissolution can be extracted. Stability protocols are developed to track the decomposition of perovskite materials in PV devices. Other methods are ultraviolet photoelectron spectroscopy (UPS) followed by X-ray electron spectroscopy (XPS), which can give information on the electronic and chemical properties of the material under consideration. Many reports focus solely on one aspect of instability, such as medium or temperature. Yet, the primary initiator and the actual decomposition process of the HPs remains unknown.