Record high external quantum efficiency of 20% achieved in fully solution-processed quantum dot light-emitting diodes based on hole-conductive metal oxides.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used as a hole injection material in quantum dot (QD) light-emitting diodes (QLEDs). However, it degrades the organic materials and electrodes in QLEDs due to its strong hydroscopicity and acidity. Although hole-conductive metal oxides have a great potential to solve this disadvantage, it is still a challenge to achieve efficient and stable QLEDs by using these solution-processed metal oxides. Herein, the state-of-the-art QLEDs fabricated by using hole-conductive MoOx QDs are achieved. The α-phase MoOx QDs exhibit a monodispersed size distribution with clear and regular crystal lattices, corresponding to high-quality nanocrystals. Meanwhile, the MoOx film owns an excellent transmittance, suitable valence band, good morphology and impressive hole-conductivity, demonstrating that the MoOx film could be used as a hole injection layer in QLEDs. Moreover, the rigid and flexible red QLEDs made by MoOx exhibit peak external quantum efficiencies of over 20%, representing a new record for the hole-conductive metal oxide based QLEDs. Most importantly, the MoOx QDs afford their QLEDs with a longer T95 lifetime than these devices made by PEDOT:PSS. As a result, we believe that the MoOx QDs could be used as efficient and stable hole injection materials used in QLEDs.

Structure, stability, electronic, magnetic, and catalytic properties of monometallic Pd, Au, and bimetallic Pd-Au core-shell nanoparticles.

Bimetallic core-shell nanoparticles (CSNPs) often exhibit excellent and tunable properties, depending on their composition, sizes, morphology, atomic arrangement, thickness, and sequence of both core and shell. In this study, the geometrical structure, thermodynamic stability, chemical activity, electronic and magnetic properties, and catalytic activity in the hydrogen evolution reaction (HER) of 13- and 55-atom Pd, Au NPs, and Pd-Au CSNPs were systematically investigated using density functional theory calculations. The results showed that Au atoms prefer to segregate to the surface-shell, while Pd atoms were inclined to aggregate in the core region for bimetallic Pd-Au CSNPs; therefore, Pd@Au CSNPs with an Au surface-shell were thermodynamically more favorable than both the monometallic Pd/Au NPs and the Au@Pd CSNPs with a Pd surface-shell. The Pd surface-shell of the Au@Pd CSNPs displayed a positive charge, while the Au surface-shell of the Au@Pd CSNPs exhibited a negative charge due to the charge transfer in the Pd-Au CSNPs, resulting in that the d-band center of Au@Pd with the Pd surface-shell showed larger shift toward the Fermi level and higher chemical activity. The Pd@Au CSNPs with the Au surface-shell showed similar d-band curves and d-band centers with monometallic Au NPs. All 13-atom Pd, Au NPs, and Pd-Au CSNPs were magnetic, while the 55-atom NPs were non-magnetic with symmetry partial density of states' curves except for Pd55. Changing the location of Pd and Au atoms in the Pd-Au CSNPs influenced their total magnetic moments. In addition, an opposite trend was found: small 13-atom NPs with a Pd surface-shell showed superior HER activity to the ones with an Au surface-shell, while large 55-atom NPs with an Au surface-shell possessed higher HER activity than the ones with a Pd surface-shell.