Perovskite light-emitting diodes (PeLEDs) have received great attention for their potential as next-generation display technology. While remarkable progress has been achieved in green, red, and near-infrared PeLEDs with external quantum efficiencies (EQEs) exceeding 20%, obtaining high performance blue PeLEDs remains a challenge. Poor charge balance due to large charge injection barriers in blue PeLEDs has been identified as one of the major roadblocks to achieve high efficiency. Here band edge control of perovskite emitting layers for blue PeLEDs with enhanced charge balance and device performance is reported. By using organic spacer cations with different dipole moments, that is, phenethyl ammonium (PEA), methoxy phenethyl ammonium (MePEA), and 4-fluoro phenethyl ammonium (4FPEA), the band edges of quasi-2D perovskites are tuned without affecting their band gaps. Detailed characterization and computational studies have confirmed the effect of dipole moment modification to be mostly electrostatic, resulting in changes in the ionization energies of ≈0.45 eV for MePEA and ≈ −0.65 eV for 4FPEA based thin films relative to PEA-based thin films. With improved charge balance, blue PeLEDs based on MePEA quasi-2D perovskites show twofold increase of the EQE as compared to the control PEA based devices.

CO adsorption on size-controlled Au nanoparticles grown on an h-BN/Rh(111) nanomesh surface has been examined to probe their potential catalytic properties. A combination of high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations demonstrate that the CO adsorption strength depends heavily on the Au deposition coverage and particle morphology. Particles resulting from low Au coverages deposited at the liquid nitrogen temperature exhibit significantly enhanced CO binding relative to bulk crystalline Au. The resulting CO TPD spectra, and the significantly red-shifted C−O stretching frequency and negative charging of the Au nanoparticles as evidenced by HREELS and DFT, all correspond to those reported for catalytically active Au nanoparticles grown on reactive metal oxides, even though the h-BN/Rh(111) surface is free of carbon, oxygen, or defects. DFT modeling further suggests that the enhanced CO adsorption occurs at highly undercoordinated Au atoms on the perimeters of the nanoparticles. As the Au coverage is increased, the CO adsorption energy and C−O stretching frequency converge toward values associated with bulk Au. Annealing to 600 K results in bulk-like CO adsorption characteristics at any Au coverage. These results suggest that the h-BN/Rh(111) surface represents a potential platform for evaluating the role of Au vs support in low-temperature CO oxidation.

The hexagonal boron nitride (h-BN) nanomesh is a promising 2D material for driving the selfassembly of metal nanoparticles with potential catalytic applications. Herein the adsorption of Au, Pt, Ag, Pd, Cu, and Ni adatoms on h-BN/Rh(111) is investigated using density functional theory (DFT) calculations to determine the ability of this pore-wire structure to facilitate the formation of size-limited, monodisperse metal nanoparticles. While all six metal atoms exhibit covalent coupling and negative charging following their adsorption in the pore region, only Au and Pt have sufficiently large diffusion barriers (> 1.2 eV) to prevent pore-to-pore diffusion at room temperature. In contrast, Ag and Cu have pore-to-pore diffusion barriers of only ~0.5 eV, while Pd and Ni show no special affinity for any specific region of the nanomesh. For verification, we have imaged Au, Pt, and Ag on h-BN/Rh(111) at room temperature and submonolayer depositions using STM. Au and Pt form numerous small nanoparticles confined to the pore regions, whereas Ag only forms a few large particles. The difference is fully consistent with the DFT predictions, indicating that our approach has the qualitatively predictive power for nanoparticle nucleation and growth behavior on the h-BN/Rh(111) nanomesh.

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Memristor devices have history-dependent charge transport properties that are ideal for neuromorphic computing applications. We reveal a memristor material and mechanism in the layered Mott insulator α-RuCl3. The pinched hysteresis loops and S-shaped negative differential resistance in bulk crystals verify memristor behavior and are attributed to a nonlinear coupling between charge injection over a Schottky barrier at the electrical contacts and concurrent Joule heating. Direct simulations of this coupling can reproduce the device characteristics.