Weiguo Hu

Bio: Weiguo Hu is an academic researcher from Tohoku University. The author has contributed to research in topics: Quantum dot & Etching (microfabrication). The author has an hindex of 12, co-authored 27 publications receiving 330 citations. Previous affiliations of Weiguo Hu include Mie University & Wuhan University.

Effects of absorption coefficients and intermediate-band filling in InAs/GaAs quantum dot solar cells

Abstract: The effects of absorption coefficients were incorporated in a detailed balance model to analyze the intermediate-band (IB) configuration in quantum dot (QD) solar cells. Our results show that the optimum IB level, EIB, depends on the ratio of two subbandgap absorption coefficient constants, αIC0/αVI0. Efficiency contour plots have been calculated to determine the optimum values of EIB and αIC0/αVI0. In many cases, a large αIC0 results in high conversion efficiency, especially for thin QD solar cells. Optimizing QD shape and size is a promising method to increase αIC0. Increasing the QD total thickness partially addresses the urgent demand for a large αIC0.

Control of optical bandgap energy and optical absorption coefficient by geometric parameters in sub-10 nm silicon-nanodisc array structure

Abstract: A sub-10?nm, high-density, periodic silicon-nanodisc (Si-ND) array has been fabricated using a new top-down process, which involves a 2D array bio-template etching mask made of Listeria-Dps with a 4.5?nm diameter iron oxide core and damage-free neutral-beam etching (Si-ND diameter: 6.4?nm). An Si-ND array with an SiO2 matrix demonstrated more controllable optical bandgap energy due to the fine tunability of the Si-ND thickness and diameter. Unlike the case of shrinking Si-ND thickness, the case of shrinking Si-ND diameter simultaneously increased the optical absorption coefficient and the optical bandgap energy. The optical absorption coefficient became higher due to the decrease in the center-to-center distance of NDs to enhance wavefunction coupling. This means that our 6?nm diameter Si-ND structure can satisfy the strict requirements of optical bandgap energy control and high absorption coefficient for achieving realistic Si quantum dot solar cells.

Quantum size effects in GaAs nanodisks fabricated using a combination of the bio-template technique and neutral beam etching.

Abstract: We successfully fabricated defect-free, distributed and sub-20-nm GaAs quantum dots (named GaAs nanodisks (NDs)) by using a novel top-down technique that combines a new bio-template (PEGylated ferritin) and defect-free neutral beam etching (NBE). Greater flexibility was achieved when engineering the quantum levels of ND structures resulted in greater flexibility than that for a conventional quantum dot structure because structures enabled independent control of thickness and diameter parameters. The ND height was controlled by adjusting the deposition thickness, while the ND diameter was controlled by adjusting the hydrogen-radical treatment conditions prior to NBE. Photoluminescence emission due to carrier recombination between the ground states of GaAs NDs was observed, which showed that the emission energy shift depended on the ND diameters. Quantum level engineering due to both diameter and thickness was verified from the good agreement between the PL emission energy and the calculated quantum confinement energy.

Simulation study of type-II Ge/Si quantum dot for solar cell applications

Abstract: The electronic structure, miniband formation conditions, and required process parameters of type-II Ge/Si quantum dots are calculated using a 3D finite element method. We further estimate the device conversion efficiency and optimize the appropriate operation conditions. By using the crystalline silicon as the matrix, the explored intermediate band solar cell (IBSC) may not be suitable for 1 sun application, but it is a great value under concentration application. By considering an appropriate H-passivation treatment on amorphous silicon, the type II Ge/Si IBSC can achieve 44.0% conversion efficiency under 1 sun application.

Plasma nanoscience: from nano-solids in plasmas to nano-plasmas in solids

Abstract: The unique plasma-specific features and physical phenomena in the organization of nanoscale soild-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter to nano-plasma effects and nano-plasmas of different states of matter.

Light upconverting core–shell nanostructures: nanophotonic control for emerging applications

Abstract: Light upconverting nanostructures employing lanthanide ions constitute an emerging research field recognized with wide ramifications and impact in many areas ranging from healthcare, to energy and, to security. The core–shell design of these nanostructures allows us to deliberately introduce a hierarchy of electronic energy states, thus providing unprecedented opportunities to manipulate the electronic excitation, energy transfer and upconverted emissions. The core–shell morphology also causes the suppression of quenching mechanisms to produce efficient upconversion emission for biophotonic and photonic applications. Using hierarchical architect, whereby each shell layer can be defined to have a specific feature, the electronic structure as well as the physiochemical structure of the upconverting nanomaterials can be tuned to couple other electronic states on the surface such as excitations of organic dye molecules or localized surface plasmons from metallic nanostructures, or to introduce a broad range of imaging or therapeutic modalities into a single conduct. In this review, we summarize the key aspects of nanophotonic control of the light upconverting nanoparticles through governed design and preparation of hierarchical shells in the core–shell nanostructures, and review their emerging applications in the biomedical field, solar energy conversion, as well as security encoding.

Plasma Nanoscience: from Nano-Solids in Plasmas to Nano-Plasmas in Solids

Abstract: The unique plasma-specific features and physical phenomena in the organization of nanoscale solid-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter, to nano-plasma effects and nano-plasmas of different states of matter.

Intermediate band solar cells: Recent progress and future directions

Abstract: Extensive literature and publications on intermediate band solar cells (IBSCs) are reviewed. A detailed discussion is given on the thermodynamics of solar energy conversion in IBSCs, the device physics, and the carrier dynamics processes with a particular emphasis on the two-step inter-subband absorption/recombination processes that are of paramount importance in a successful implementation high-efficiency IBSC. The experimental solar cell performance is further discussed, which has been recently demonstrated by using highly mismatched alloys and high-density quantum dot arrays and superlattice. IBSCs having widely different structures, materials, and spectral responses are also covered, as is the optimization of device parameters to achieve maximum performance.