Organolead halide perovskite nanocrystals (NCs) have emerged as promising materials for various optoelectronic applications. However, their practical applications have been limited due to low structural integrity and poor luminescence stability associated with fast attachment−detachment dynamics of surface capping molecules during postprocessing. At present, a framework for understanding how the functional additives interact with surface moieties of organolead halide perovskites is not available. Methylammonium lead bromide NCs without surfactants on their surface provide an ideal system to investigate the direct interactions of the perovskite with functional molecules. When the oleic acid is used in a combination with n-octylamine, its contribution to surface passivation is significantly increased by protonating the alkyl amine to the corresponding ammonium ion. Our results demonstrate that the Br vacancies at the nonpassivated surface result in a reduction of Pb 2+ to Pb 0 by trapping electrons generated from the exciton dissociation, which provides a main pathway for exciton trapping.

Ligand-assisted ball milling has attracted lot of attention due to its ability for the scalable synthesis of nanoscale organic−inorganic perovskite (OIP) materials. We found that this technique can be successfully extended for the formation of ternary OIP nanocrystals (NCs) as well as doping of transition-metal cations into the host OIP NCs. Here, a wide range of compositional variation of halogen anions (X = Cl − , Br − , I − ) as well as doping of transition-metal cations (Mn 2+ ) could be achieved by ligand-assisted ball milling, demonstrating that the strategies for cation/anion exchange can be applied to the large-scale synthesis of OIP NCs to control their photoluminescence emission and bandgap energies. Therefore, this technique provides a lowcost and facile route for mass production of exfoliated OIP NCs to overcome the most prominent challenges for future advances of OIP materials.

No abstract

All-inorganic lead halide perovskite (IHP) nanocrystals (NC) have demonstrated to be a promising active material in a wide range of optoelectronic applications due to their chemical and thermal stability compared to organicinorganic perovskite NCs. However, the synthetic procedure of IHP NC generally requires a high-temperature reaction of the precursors due to their limited solubility. Alternatively, the affinity of the precursor elements to the solvent was controlled to enhance their solubility in the liquid phase, and thus the enhanced kinetics in the crystallization process. Here, we show how the controlled solubility of Cs salts (i. e., Cs halide, acetate, carbonate) influences on their crystallization process and their optical properties. The formation of highly luminescent CsPbX 3 (X=Cl, Br, and mixed Br/Cl and Br/ I) NCs with a well-controlled crystallinity and morphology provide fundamental insights into their crystallization process, broadening their applications in the optoelectronic devices.

Formation of the additional 2-D (MA)2MnCl4 phase suppresses the efficient Mn2+ doping into halide perovskite structures during the reprecipitation process.

Preferential attraction of polymer chains to the substrate [i.e., poly­(methyl methacrylate) (PMMA) on the hydroxyl-terminated Si substrate] typically results in the initial phase separation of spin-cast immiscible linear polymer blends [i.e., polystyrene (PS)/PMMA] with a characteristic interfacial microstructure depending on their molecular weight. A formation of the undesired microstructure in those blends is inevitable because of the thermodynamic force driving their phase separation combined with relatively rapid dynamics in solution. In contrast, the polymer ligands, which are grafted from nanoparticles, are capable of limited segmental interactions in the presence of segmental contacts of chemically distinct chains as well as hindered mobility by interpenetration (or entanglement) and thus exhibit a homogeneous but non-equilibrium phase behavior. Here, the microstructure of the blends consisting of immiscible polymer-grafted nanoparticles (PGNPs) was identified by their neutron reflectivity, in which the scattering length density was controlled by tethering deuterated PS on silica NPs. We demonstrate that the single-phase homogeneous microstructure is attributed to a significantly reduced particle dynamics arising from the cooperative motion (or interpenetration) of polymer ligands during vitrification of PGNP films despite a relatively high degree of segregation NχS/MMA. Furthermore, the slower segmental interactions of polymer ligands promote the thermal stability of the PGNP blends in the kinetically quenched non-equilibrium state. This suggests a crucial role of polymer ligands to determine the relevant properties relying on their microstructures in a wide range of blending approaches utilizing nanoparticles and polymers.

No abstract

No abstract