We report an amine-free synthesis of lead halide perovskite (LHP) nanocrystals, using trioctylphosphine oxide (TOPO) instead of aliphatic amines, in combination with a protic acid (e.g., oleic acid). The overall synthesis scheme bears many similarities to the chemistry behind the preparation of LHP thin films and single crystals, in terms of ligand coordination to the chemical precursors. The acidity of the environment and hence the extent of protonation of the TOPO molecules tune the reactivity of the PbX 2 precursor, regulating the size of the nanocrystals. On the other hand, TOPO molecules are virtually absent from the surface of our nanocrystals, which are simply passivated by one type of ligand (e.g., Cs-oleate). Furthermore, our studies reveal that Cs-oleate is dynamically bound to the surface of the nanocrystals and that an optimal surface coverage is critical for achieving high photoluminescence quantum yield. Our scheme delivers NCs with a controlled size and shape: only cubes are formed, with no contamination with platelets, regardless of the reaction conditions that were tested. We attribute such a shape homogeneity to the absence of primary aliphatic amines in our reaction environment, since these are known to promote the formation of nanocrystals with sheet/platelet morphologies or layered phases under certain reaction conditions. The TOPO route is particularly appealing with regard to synthesizing LHP nanocrystals for large-scale manufacturing, as the yield in terms of material produced is close to the theoretical limit: i.e., almost all precursors employed in the synthesis are converted into nanocrystals.

Metal halide perovskites are promising candidates for use in light emitting diodes (LEDs), due to their potential for colour tuneable and high luminescence efficiency. While recent advances in perovskite-based light emitting diodes have resulted in external quantum efficiencies exceeding 12.4 % for the green emitters, and infrared emitters based on 3D/2D mixed dimensional perovskites have exceeded 20%, the external quantum efficiencies of the red and blue emitters still lag behind. A critical issue to date is creating highly emissive and stable perovskite emitters with the desirable emission band gap to achieve full-colour displays and white LEDs. Herein, we report the preparation and characterization of a highly luminescent and stable suspension of cubic-shaped methylammonium lead triiodide CH 3 NH 3 PbI 3 perovskite nanocrystals, where we synthesise the nanocrystals via a ligand-assisted re-precipitation technique, using an acetonitrile/methylamine compound solvent system to solvate the ions, and toluene as the anti-solvent to induce crystallisation. Through tuning the ratio of the ligands, the ligand to toluene ratio, and the temperature of the toluene, we obtain a solution of CH 3 NH 3 PbI 3 nanocrystals with a photoluminescence quantum yield exceeding 93%, and tuneable emission between 660 nm and

Nanocrystal (NC) self-assembly is a versatile platform for materials engineering at the mesoscale. The NC shape anisotropy leads to structures not observed with spherical NCs. This work presents a broad structural diversity in multicomponent, long-range ordered superlattices (SLs) comprising highly luminescent cubic CsPbBr 3 NCs (and FAPbBr 3 NCs) coassembled with the spherical, truncated cuboid, and disk-shaped NC building blocks. CsPbBr 3 nanocubes combined with Fe 3 O 4 or NaGdF 4 spheres and truncated cuboid PbS NCs form binary SLs of six structure types with high packing density; namely, AB 2 , quasi-ternary ABO 3 , and ABO 6 types as well as previously known NaCl, AlB 2 , and CuAu types. In these structures, nanocubes preserve orientational coherence. Combining nanocubes with large and thick NaGdF 4 nanodisks results in the orthorhombic SL resembling CaC 2 structure with pairs of CsPbBr 3 NCs on one lattice site. Also, we implement two substrate-free methods of SL formation. Oil-in-oil templated assembly results in the formation of binary supraparticles. Self-assembly at the liquid–air interface from the drying solution cast over the glyceryl triacetate as subphase yields extended thin films of SLs. Collective electronic states arise at low temperatures from the dense, periodic packing of NCs, observed as sharp red-shifted bands at 6 K in the photoluminescence and absorption spectra and persisting up to 200 K.

The formation of nanocrystals is at the heart of various scientific disciplines, but the atomic mechanisms underlying the early stages of crystallization from supersaturated solutions are still rather unclear. Here, we used in situ liquid-phase scanning transmission electron microscopy to study at the atomic level the very early stages of gold nanocrystal growth, and the evolution of its crystallinity. We found that the nucleation is initiated by the formation of poorly crystalline nanoparticles. These are transformed into monocrystals via nanocrystallization governed by a complex process of multiple out-and-in exchanges of matter between a crystalline-core and a disordered-shell, referred to as the cluster-cloud. Our observations at the crystal/cluster-cloud interface during growth demonstrate that the initially formed nanocrystals expel the poorly crystallized phases as nanoclusters into the cluster-cloud, then readsorb it by two distinct pathways, namely, by (i) monomer attachments and (ii) nanocluster coalescence. This growth process eventually leads to the formation of monocrystalline nanoparticles.

All-inorganic perovskite materials are attractive alternatives to organic-inorganic perovskites because of their potential for higher thermal stability. Although CsPbI 3 is compositionally stable under elevated temperatures, the cubic perovskite α-phase is thermodynamically stable only at >330 C and the low-temperature perovskite γ-phase is metastable and highly susceptible to nonperovskite δ-phase conversion in moisture. Many methods have been reported which show that the incorporation of acid (aqueous HI) or "HPbI 3 "-recently shown to be dimethylammonium lead iodide (DMAPbI 3)-lowers the annealing temperature required to produce the black, perovskite phase of CsPbI 3. Herein, the optical and crystallographic data presented show that dimethylammonium (DMA) can successfully incorporate as an A-site cation to replace Cs in the CsPbI 3 perovskite material. This describes the stabilization and lower phase transition temperature reported in the literature when HI or HPbI 3 is used as precursors for CsPbI 3. The Cs-DMA alloy only forms a pure-phase material up to %25% DMA; at higher concentrations, the CsPbI 3 and DMAPbI 3 begin to phase segregate. These alloyed materials are more stable to moisture than neat CsPbI 3 , but do not represent a fully inorganic perovskite material.