Mn 2+ ions, occupying the substitution position, are preferably incorporated during perovskite nanocrystal formation.

High temperature colloidal synthesis for obtaining thermal, colloidal and phase-stable CsPbI nanocrystals with near-unity quantum yield is reported. While standard perovskite synthesis reactions were carried out at 160 °C (below 200 °C), increase of another ≈100 °C enabled the alkylammonium ions to passivate the surface firmly and prevented the nanocrystals from phase transformation. This did not require any inert atmosphere storage, use of heteroatoms, specially designed ligands, or the ice cooling protocol. Either at high temperature in reaction flask or in the crude mixture or purified dispersed solution; these nanocrystals were observed stable and retained the original emission. Different spectroscopic analyses were carried out and details of the surface binding of alkyl ammonium ligands in place of surface Cs in the crystal lattice were investigated. As CsPbI is one of the most demanding optical materials, bringing stability by proper surface functionalization without use of secondary additives would indeed help in wide spreading of their applications.

For fast separation of the photogenerated charge carriers, metal semiconductor heterostructures have emerged as one of the leading materials in recent years. Among these, metal Au coupled with low bandgap semiconductors remain as ideal materials where both can absorb the solar light in the visible region. It is also established that on excitation, the plasmonic state of gold interacts with excited state of semiconductor and helps for the delocalization of the photogenerated electrons. Focusing these materials where electron transfer preferably occurs from semiconductor to metal Au on excitation, in this Perspective, we report the latest developments in the synthetic chemistry in designing such nano heterostructures and discuss their photocatalytic activities in organic dye degradation/reduction and/or photocatalytic water splitting for generation of hydrogen. Among these, materials such as Au-CZTS, Au-SnS, Au-Bi2S3, Au-ZnSe, and so forth are emphasized, and their formation chemistry as well as their photocatalytic activities are discussed in this Perspective.

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For varying the size of perovskite nanocrystals, variation in the reaction temperature and tuning the ligand chain lengths are established as the key parameters for hightemperature solution-processed synthesis. These also require sharp cooling for obtaining desired dimensions and optical stability. In contrast, using preformed alkylammonium bromide salt as the precise dimension-controlling reagent, wide window size tunable CsPbBr 3 nanocrystals were reported without varying the reaction temperature or changing the ligands. The size tunability even with ∼1 nm step growth regimes was achieved as a function of only the concentration of added alkylammonium bromide salt. Not only the cube shape but also the width varied in the sheet structures. Because these nanostructures lose their optical stability and crystal phase on prolonged annealing, stabilizing these in high-temperature synthesis for all-inorganic lead halide perovskites is important and remains challenging. In this aspect, this method proved to be more facile because it does not require sharp cooling, and the nanocrystals retained their phase and optical properties even upon prolonged annealing.