“…The great success of perovskite as a new generation of semiconducting materials has been widely witnessed in photovoltaics, light-emitting diodes (LEDs), transistors, photodetectors, and lasers. − With general chemical stoichiometry ABX 3 , perovskite is typically composed of cation A, metal cation B, and halide anion X. The wide feasibility of the combination of different cations and halide anions in perovskites has promoted large possibilities in compositional engineering for different applications. − There are several synthesis strategies for organic–inorganic hybrid perovskite nanomaterials, including the template method, hot injection method, ligand-assisted reprecipitation strategy, chemical vapor deposition method, microfluidic reactor method, ultrasound synthesis, and mechanical ball milling method. − In perovskite materials, the A-site cation, such as methylammonium (CH 3 NH 3 , MA), formamidinium (HC(NH 2 ) 2 , FA), or caesium (Cs), as an important effective component, plays a key role in tuning the crystal structure and optical and electronic properties. For example, Br vacancies and interstitials have much lower formation energies and higher density in MA cation-based perovskite than FA-based crystals, while a higher rotation barrier and stronger H-bonding between the organic cation and Br are in the latter case .…”