The dependence of the polarization-induced electric field in GaInN/GaN multiplequantum-well light-emitting diodes (LEDs) on the GaN quantum barrier (QB) thickness is investigated. Electrostatic arguments and simulations predict that a thin QB thickness reduces the electric field in the quantum wells (QWs) and also improves the LED efficiency. We experimentally demonstrate that the QW electric field decreases with decreasing QB thickness. The lower electric field results in a better overlap of electron and hole wave functions and better carrier confinement in the QWs. A reduced efficiency droop and enhanced internal quantum efficiency is demonstrated for GaInN/GaN LEDs when the QB thickness is reduced from 24.5 to 9.1 nm.

Photo-electrodes with tailored three-dimensional nanostructures offer a large enhancement in light harvesting capability for various optoelectronic devices enabled by strong light scattering in the nanostructures as well as improved charge transport. Here we present an array of three-dimensional titanium dioxide (TiO₂) nanohelixes fabricated by the oblique angle deposition method as a multifunctional photoanode for CdSe quantum dot sensitized solar cells (QDSSCs). The CdSe QDSSC with a TiO₂ nanohelix photoanode shows a 100% higher power conversion efficiency despite less light being absorbed in CdSe QDs when compared with a conventional TiO₂ nanoparticle photoanode. We attribute the higher power conversion efficiency to strong light scattering by the TiO₂ nanohelixes and much enhanced transport and collection of photo-generated carriers enabled by the unique geometry and near-single crystallinity of the TiO₂ nanohelix structure.

We report a method to precisely control the atomic defects at grain boundaries (GBs) of monolayer MoS 2 by vapor−liquid−solid (VLS) growth using sodium molybdate liquid alloys, which serve as growth catalysts to guide the formations of the thermodynamically most stable GB structure. The Mo-rich chemical environment of the alloys results in Mopolar 5|7 defects with a yield exceeding 95%. The photoluminescence (PL) intensity of VLS-grown polycrystalline MoS 2 films markedly exceeds that of the films, exhibiting abundant S 5|7 defects, which are kinetically driven by vapor−solid−solid growths. Density functional theory calculations indicate that the enhanced PL intensity is due to the suppression of nonradiative recombination of charged excitons with donor-type defects of adsorbed Na elements on S 5|7 defects. Catalytic liquid alloys can aid in determining a type of atomic defect even in various polycrystalline 2D films, which accordingly provides a technical clue to engineer their properties.

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