Graphene controlled Brewster angle device for ultra broadband terahertz modulation

Terahertz modulators with high tunability of both intensity and phase are essential for effective control of electromagnetic properties. Due to the underlying physics behind existing approaches there is still a lack of broadband devices able to achieve deep modulation. Here, we demonstrate the effect of tunable Brewster angle controlled by graphene, and develop a highly-tunable solid-state graphene/quartz modulator based on this mechanism. The Brewster angle of the device can be tuned by varying the conductivity of the graphene through an electrical gate. In this way, we achieve near perfect intensity modulation with spectrally flat modulation depth of 99.3 to 99.9 percent and phase tunability of up to 140 degree in the frequency range from 0.5 to 1.6 THz. Different from using electromagnetic resonance effects (for example, metamaterials), this principle ensures that our device can operate in ultra-broadband. Thus it is an effective principle for terahertz modulation

Recycling spent lead-acid battery into lead halide for resource purification and multifunctional perovskite diode

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Uncovering the Electron‐Phonon Interplay and Dynamical Energy‐Dissipation Mechanisms of Hot Carriers in Hybrid Lead Halide Perovskites

The discovery of slow hot carrier cooling in hybrid organic–inorganic lead halide perovskites (HOIPs) has provided exciting prospects for efficient solar cells that can overcome the Shockley–Queisser limit. Questions still loom over how electron‐phonon interactions differ from traditional polar semiconductors. Herein, the electron‐phonon coupling (EPC) strength of common perovskite films (MAPbBr3, MAPbI3, CsPbI3, and FAPbBr3) is obtained using transient absorption spectroscopy by analyzing the hot carrier cooling thermodynamics via a simplified two‐temperature model. Density function theory calculations are numerically performed at relevant electron‐temperatures to confirm experiments. Further, the variation of carrier‐temperature over a large range of carrier‐densities in HOIPs is analyzed, and an “S‐shaped” dependence of the initial carrier‐temperature to carrier‐density is reported. The phenomenon is attributed to the dominance of the large polaron screening and the destabilization effect which causes an increasing‐decreasing fluctuation in temperature at low excitation powers ; and a hot‐phonon bottleneck which effectively increases the carrier temperature at higher carrier‐densities. The turning point in the relationship is indicative of the critical Mott density related to the nonmetal‐metal transition. The EPC analysis provides a novel perspective to quantify the energy transfer in HOIPs, electron‐lattice subsystem, and the complicated screening‐bottleneck interplay is comprehensively described, resolving the existing experimental contradictions

Morphology-conserved transformation: synthesis of hierarchical mesoporous nanostructures of Mn(2)O(3) and the nanostructural effects on Li-ion insertion/deinsertion properties

By means of morphology-conserved transformation, we have synthesized hierarchically structured Mn(2)O(3) nanomaterials with different morphologies and pore structures. The key step of this method consists of the formation of a precursor containing the target materials interlaced with the judiciously chosen polyol-based organic molecules, which are subsequently knocked out to generate the final nanomaterials. In the present work, two kinds of precursor morphologies, oval-shaped and straw-sheaf-shaped, have been selectively prepared by hydrothermal treatment of different functional polyol molecules (oval-shape with fructose and straw-sheaf-shape with beta-cyclodextrin) and potassium permanganate. Thermal decomposition of the precursors resulted in the formation of mesoporous Mn(2)O(3) maintaining the original morphologies, as revealed by extensive characterization. These novel hierarchical nanostructures with different pore sizes/structures prompted us to examine their potential as anode materials for lithium ion batteries (LIBs). The electrochemical results with reference to LIBs show that both of our mesoporous Mn(2)O(3) nanomaterials deliver high reversible capacities and excellent cycling stabilities at a current density of 200 mA g(-1) compared to the commercial Mn(2)O(3) nanoparticles. Moreover, the straw-sheaf-shaped Mn(2)O(3) exhibits a higher specific capacity and a better cycling performance than the oval-shaped one, due to the relatively higher surface area and the peculiar nanostrip structure resulting in the reduced length for lithium ion diffusion. Morphology-conserved transformation yields two kinds of hierarchical mesoporous Mn(2)O(3) nanomaterials with high capacities and cycling stabilities for lithium ion batteries.NSFC/HK-RGC[NSFC 20931160426, N_HKUST609/09]; HK-RGC[HKUST 604809, 605710

Significantly Enhanced Open Circuit Voltage and Fill Factor of Quantum Dot Sensitized Solar Cells by Linker Seeding Chemical Bath Deposition

We have significantly improved open circuit voltage and fill factor with a Pt counter electrode of quasi-solid state quantum dot sensitized solar cells (QDSSCs) by achieving compact coverage of QDs on a TiO2 matrix through a linker seeding chemical bath deposition process, leading to 4.23% power conversion efficiency, nearly two times that with conventionally deposited control photoanode. The distinguishing characteristic of our linker seeding synthesis is that it does not rely on surface adsorption of precursor ions directly on TiO2 (T2O2 similar to Cdx) but rather nucleates special ionic seeds on a compact linker layer (TiO2-COORS-Cdx), thereby resulting in a full and even coverage of QDs on the TiO2 surface in large area. We have shown that the compact coverage not only helps to suppress recombination from electrolyte but also gives rise to better charge transport through the QD layer. This linker seeding chemical bath deposition method is general and expected to reinforce the hope of quasi-solid state QDSSCs as a strong competitor of dye-sensitized solar cells after further optimization and development

One-pot Synthesis of Mesoporous TiO2 from Self-Assembled Sol Particles and Its Application as Mesoscopic Photoanodes of Dye-Sensitized Solar Cells

A facile one-pot synthetic strategy is developed to prepare a class of highly crystalline TiO2 materials with uniform mesoporous structure and good thermal stability. The synthesis intricately combines the advantages of the Stober, surfactant-templated, and hydrothermal methods. The mesopore sizes are well controlled by adjusting the ratio of hydrolysis inhibitor to TiO2 precursor. DSSC testing results highlights the importance of specific surface area and mesopore size to the cell performance. The DSSC based on the optimized mesoporous TiO2 photoanode reached over 8.3% power conversion efficiency. It is revealed that electron lifetime is greatly increased because of the confinement effect of the uniform mesoporous structure associated with the photoanode. Electron transport is also accelerated as a result of the highly connected crystalline structure for electron transport. Electron diffusion length on the optimized photoanode is about 2.3times larger than that in a photoanode of DegussaP25

Unveiling Two Electron-Transport Modes in Oxygen-Deficient TiO2 Nanowires and Their Influence on Photoelectrochemical Operation

Introducing oxygen vacancies (V-O) into TiO2 materials is one of the most promising ways to significantly enhance light-harvesting and photocatalytic efficiencies of photoelectrochemical (PEC) cells for water splitting among others. However, the nature of electron transport in V-O-TiO2 nanostructures is not well understood, especially in an operating device. In this work, we use the intensity-modulated photocurrent spectroscopy technique to study the electron-transport property of V-O-TiO2 nanowires (NWs). It is found that the electron transport in pristine TiO2 NWs displays a single trap-limited mode, whereas two electron-transport modes were detected in V-O-TiO2 NWs, a trap-free transport mode at the core, and a trap-limited transport mode near the surface. The considerably higher diffusion coefficient (D-n) of the trap-free transport mode grants a more rapid electron flow in V-O-TiO2 NWs than that in pristine TiO2 NWs. This electron-transport feature is expected to be common in other oxygen-deficient metal oxides, lending a general strategy for promoting the PEC device performance

Significantly Enhanced Open Circuit Voltage and Fill Factor of Quantum Dot Sensitized Solar Cells by Linker Seeding Chemical Bath Deposition

We have significantly improved open circuit voltage and fill factor with a Pt counter electrode of quasi-solid state quantum dot sensitized solar cells (QDSSCs) by achieving compact coverage of QDs on a TiO₂ matrix through a linker seeding chemical bath deposition process, leading to 4.23% power conversion efficiency, nearly two times that with conventionally deposited control photoanode. The distinguishing characteristic of our linker seeding synthesis is that it does not rely on surface adsorption of precursor ions directly on TiO₂ (TiO₂∼Cd_<i>x</i>) but rather nucleates special ionic seeds on a compact linker layer (TiO₂-COORS-Cd_<i>x</i>), thereby resulting in a full and even coverage of QDs on the TiO₂ surface in large area. We have shown that the compact coverage not only helps to suppress recombination from electrolyte but also gives rise to better charge transport through the QD layer. This linker seeding chemical bath deposition method is general and expected to reinforce the hope of quasi-solid state QDSSCs as a strong competitor of dye-sensitized solar cells after further optimization and development

Self-assembly of Ni2P nanowires as high-efficiency electrocatalyst for dye-sensitized solar cells

We report an easy way to assemble porous one-dimensional (1D) Ni2P nanowires through phosphatization of a Ni(SO4)(0.3)(OH)(1.4) nanobelt precursor. The peculiar synthetic process endows the Ni2P nanowires with large surface area, hierarchical porous structure and the ability to form closely connected network for transporting both electrons and electrolytes, which in conjunction with the high intrinsic electrocatalytic activity make it an excellent low-cost counter electrode material for dye-sensitized solar cells (DSSCs). Indeed, the first investigation of such novel counter electrode for DSSC presented superb photovoltaic performance rivaling the conventional Pt counter electrode