Mixed Ligand Passivation as the Origin of Near-Unity Emission Quantum Yields in CsPbBr Nanocrystals.

Key features of syntheses, involving the quaternary ammonium passivation of CsPbBr nanocrystals (NCs), include stable, reproducible, and large (often near-unity) emission quantum yields (QYs). The archetypical example involves didodecyl dimethyl ammonium (DDDMA)-passivated CsPbBr NCs where robust QYs stem from interactions between DDDMA and NC surfaces. Despite widespread adoption of this synthesis, specific ligand-NC surface interactions responsible for large DDDMA-passivated NC QYs have not been fully established.

Excitation Intensity- and Size-Dependent Halide Photosegregation in CsPb(IBr) Perovskite Nanocrystals.

Although broad consensus exists that photoirradiation of mixed-halide lead perovskites leads to anion segregation, no model today fully rationalizes all aspects of this near ubiquitous phenomenon. Here, we quantitatively compare experimental, CsPb(IBr) nanocrystal (NC) terminal anion photosegregation stoichiometries and excitation intensity thresholds to a band gap-based, thermodynamic model of mixed-halide perovskite photosegregation. Mixed-halide NCs offer strict tests of theory given physical sizes, which dictate local photogenerated carrier densities.

Band alignment at interfaces of two-dimensional materials: internal photoemission analysis.

The article overviews experimental results obtained by applying internal photoemission (IPE) spectroscopy methods to characterize electron states in single- or few-monolayer thick two-dimensional materials and at their interfaces. Several conducting (graphene) and semiconducting (transitional metal dichalcogenides MoS, WS, MoSe, and WSe) films on top of thermal SiOhave been analyzed by IPE, which reveals significant sensitivity of interface band offsets and barriers to the details of the material and interface fabrication, indicating violation of the Schottky-Mott rule. This variability is associated with charges and dipoles formed at the interfaces with van der Waals bonding as opposed to the chemically bonded interfaces of three-dimensional semiconductors and metals.