Ultimate Efficiency Research Articles

Characteristics of eco-friendly perovskite solar cell with moth-eye nanostructure array

A novel design of tin perovskite (CH3NH3SnI3) solar cell (PSC) is proposed and analyzed for energy harvesting application. The suggested PSC is lead free where moth-eye nanostructures are implemented in the active material to improve the light trapping and hence the light absorption. The suggested SC is numerically studied using finite difference time domain (FDTD) via Lumerical software package. The geometrical parameters and position of the nanostructures are studied to maximize the absorption and hence the optical efficiency. The reported PSC covered by the moth-eye nanostructures exhibits marked light trapping compared to the conventional planar structure with photocurrent density of 46.0082 (mA/cm2), an optical generation rate of 3.38 e28 (m−3. s−1) and an ultimate efficiency of 31.76%. Therefore, an enhancement of 14.496% is obtained compared to the traditional PSC due to the localized surface plasmons (LSP) modes around the moth eye nanostructures. The suggested design is an efficient replacement to lead—perovskite owing to excellent photovoltaic properties, cheap fabrication cost, suitable band gap of 1.02 eV, eco-friendly and great performance in converting sunlight to electrical energy.

Bright and Efficient Light-Emitting Devices Based on 2D Transition Metal Dichalcogenides.

2D monolayer transition metal dichalcogenides (TMDCs) show great promise for the development of next-generation light-emitting devices owing to their unique electronic and optoelectronic properties. The dangling-bond-free surface and direct-bandgap structure of monolayer TMDCs allow for near-unity photoluminescence quantum efficiencies. The excellent mechanical and optical characteristics of 2D TMDCs offer great potential to fabricate TMDC-based light-emitting diodes (LEDs) featuring good flexibility and transparency. Great progress has been made in the fabrication of bright and efficient LEDs with varying device structures. In this review, the aim is to provide a comprehensive summary of the state-of-the-art progress made in the construction of bright and efficient LEDs based on 2D TMDCs. After a brief introduction to the research background, the preparation of 2D TMDCs used for LEDs is briefly discussed. The requirements and the corresponding challenges to achieve bright and efficient LEDs based on 2D TMDCs are introduced. Thereafter, various strategies to enhance the brightness of monolayer 2D TMDCs are described. Following that, the carrier-injection schemes enabling bright and efficient TMDC-based LEDs along with the device performance are summarized. Finally, the challenges and future prospects regarding the accomplishment of TMDC-LEDs with ultimate brightness and efficiency are discussed.

Effect of pore-throat structure on air-foam flooding performance in a low-permeability reservoir

In this study, effect of pore-throat structure on air-foam displacement performance in a low-permeability reservoir has been experimentally examined. More specifically, porosity and permeability of samples collected from the Upper Triassic Yanchang Formation of the Chang 6 low-permeability oil reservoir in the Ordos Basin, China, were measured, and then their petrological and petrophysical properties as well as pore and throat size distributions were determined by integrating thin-section analysis, x-ray diffraction analysis, high-pressure mercury injection (HMI) and rate-controlled mercury injection (RMI) tests, and NMR technique. Based on the ultimate displacement efficiency and the measured washing efficiency, the underlying recovery mechanisms associated with air-foam flooding in two sub-member samples which have different pore-throat distributions (i.e., sample C6-1: Concentrated throat distribution and sample C6-2: Dispersed throat distribution) are rather different, implying that the timing for converting water injection to air-foam flooding shall be different as well. Also, the difference of throat-distribution characteristics between sub-members C6-1 and C6-2 is found to impose a great but different influence on the air-foam displacement performance by improving their oil washing and microscopic sweep efficiencies, respectively. This finding is of a great significance to help design, evaluate, and optimize the injection-production strategies in a low-permeability reservoir with different pore-throat distributions.

Toward Near-Foldable Surface Light Sources with Ultimate Efficiency: Ultrathin Substrates Embedded with Micron-Scale Inverted Lens Arrays

Foldable organic light-emitting diodes (OLEDs) are essential building blocks for portable devices with expandable screens as well as more futuristic systems such as wearable or body-attachable electronic devices. Although various approaches have been proposed to realize foldable OLEDs, the efficiency enhancement techniques developed for their rigid counterparts are not always applicable due to the strict thickness limitations, making it challenging to achieve very high efficiency in a foldable OLED. Here, we propose ultrathin substrates embedded with an inverted microlens array (IMLA) as a platform on which to design and realize OLEDs that can be bent at sub-100 μm bending radius while also exhibiting very high light outcoupling efficiency. By noting the periodic arrangement of the patterns in the IMLA, the potential effects of optical diffraction on the overall emission pattern and efficiency enhancement are carefully analyzed by incorporating a bidirectional scattering distribution function via a trans-scale approach. Neutral-plane engineering is also done with finite element method simulations that examine the effect of the IMLA structures on the local modulation of the strain and stress in ultrathin devices, where the feature size of the IMLA is comparable to the overall thickness of the whole device. With the proposed method, highly efficient foldable OLEDs are demonstrated that show the maximum external quantum efficiency to be as high as 58% without optical side effects and that can withstand 10,000 trials of repeated folding cyclic tests at a bending radius of 50 μm.

Biochar-supported magnesium oxide as high-efficient lead adsorbent with economical use of magnesium precursor

With unique porous structure inherited from lignocellulose, biochar was an appropriate carrier for small-size MgO materials, which could simplify the synthetic process and better solve agglomeration and separation problems during adsorption. Biochar-supported MgO was prepared with impregnation method. Under different synthesis conditions, the obtained MgO presented diverse properties, and moderate pyrolysis condition was conducive to the improvement of Mg conversion rate. The Pb(II) capacity was highly correlated with Mg content, rather than the specific surface area. Reducing the pyrolysis temperature or increasing the usage of supporter could improve adsorption efficiency when using Mg content-normalized capacity as the criterion. The better release ability of Mg, contribute by the higher extent of hydration and better spread of MgO, were the critical factors. The maximal Mg content-normalized capacity could reach 0.932 mmol·mmol-Mg−1 with the mass ratio of biochar/MgCl2·6H2O = 4:1 at the pyrolysis temperature of 600 °C. Considering the ultimate utilization efficiency of Mg in precursor, the optimum Mg consumption-normalized capacity was 0.744 mmol·mmol-Mg−1 with the mass ratio of biochar/MgCl2·6H2O = 1:1 at 600 °C.

Investigation of Fracturing Fluid Flowback in Hydraulically Fractured Formations Based on Microscopic Visualization Experiments

Fracturing fluids are widely applied in the hydraulic fracturing of shale gas reservoirs, but the fracturing fluid flowback efficiency is typically less than 50%, severely limiting the shale gas recovery. Additionally, the mechanism and main influencing factors of fracturing fluid flowback are unclear. In this study, microscopic experiments are conducted to simulate the fracturing fluid flowback progress in shale gas reservoirs. The mechanism and factors affecting fracturing fluid flowback/retention in the fracture zone were analyzed and clarified. Results show that the ultimate flowback efficiency of fracturing fluid is positively correlated with the fracturing fluid concentration and the gas driving pressure difference. There are four kinds of mechanisms responsible for fracturing fluid retention in the pore network: viscous resistance, the Jamin effect, the gas blockage effect and the dead end of the pore. Additionally, the ultimate flowback efficiency of the fracturing fluid increases linearly with increasing capillary number. These insights will advance the fundamental understanding of fracturing fluid flowback in shale gas reservoirs and provide useful guidance for shale gas reservoirs development.

Inverse design of GaAs nanowire array solar cell structures with nonuniform diameters

Non-uniform diameter GaAs nanowire array solar cell structures are designed using the particle swarm optimized inverse design method. The results show that unlike the uniform diameter structure, which has a series of absorption valleys, the absorption spectra of the non-uniform structures are much flatter, which is attributed to a combination of absorption spectra from nanowires of different diameters. For the same height, the optimized structure with non-uniform diameter yields a remarkable ultimate efficiency of 34.3%, 1.1% higher than that the structure with uniform diameter, mainly due to the enhanced absorption at long wavelengths. For the same volume, an even higher ultimate efficiency of 34.6% is obtained, due to the enhanced absorption over almost the entire wavelength range. This work could pave the way for the design of low-cost high-efficiency nanoscale solar cells and other photoelectric conversion devices.

Improving Methane Production from Waste Activated Sludge Assisted by Fe(II)-Activated Peroxydisulfate Pretreatment via Anaerobic Digestion: Role of Interspecific Syntrophism Mediated by Sulfate-Reducing Bacteria

Sulfate radical generated via peroxydisulfate (PDS) activation has been extensively applied to energy recovery from waste activated sludge (WAS) during anaerobic digestion (AD), while the residual sulfate is still a limitation for its further application. In this study, a novel coupling strategy of Fe(II)-activated PDS pretreatment [Fe(II)_PDS] with sulfate-reducing bacteria (SRB) mediated was explored to enhance methane yield from WAS during AD. Results showed that the similar methane yield was obtained in Fe(II)_PDS + SRB (16.6 mL/g VSS) and zero-valent iron (ZVI)_PDS + SRB (16.9 mL/g VSS), which enhanced by 19.9–56.5% than other groups, while the hydrolysis rate constant (0.0065 h–1) in Fe(II)_PDS + SRB was much higher than that observed in ZVI_PDS + SRB (0.0046 h–1). Meanwhile, the concentration of short-chain fatty acids (SCFAs) peaked at 360.9 mg COD/g VSS (5 d) in the Fe(II)_PDS + SRB group, with the acetic acid (HAc) and propionic acid (HPr) accumulative proportion of 73.5%, and the total concentration promoted by 28.5% than that of the ZVI_PDS + SRB group, which provided a more ideal substrate for methanogens. The ultimate utilization efficiency of SCFAs reached 62.4% in the Fe(II)_PDS + SRB group. Moreover, MiSeq sequencing, canonical correspondence analysis, and molecular ecological network analysis revealed the intrinsic interaction of the functional microbial consortia, that is, anaerobic fermentation bacteria, SRB, nitrate-reducing bacterium, and acetotrophic methanogen, with the abundances of 9.52, 2.4, 4.93, and 77.7% in the Fe(II)_PDS + SRB group. Considering the treatment performance and the difficulty of the subsequent disposal, Fe(II) may be the superior activator than ZVI for free radicals (i.e., SO4•– and HO•) generation from PDS and further played the important role for interspecific syntrophism coupling with SRB during AD. Results of this study may provide a promising way for energy recovery from WAS.

Optical performance analysis of InP nanostructures for photovoltaic applications.

In this article, we have performed a comparative analysis of six different types of nanostructures that can improve photon management for photovoltaic applications. These nanostructures act as anti-reflective structures by improving the absorption characteristics and tailoring the optoelectronic properties of the associated devices. The absorption enhancement in indium phosphide (InP) and silicon (Si) based cylindrical nanowires (CNWs) and rectangular nanowires (RNWs), truncated nanocones (TNCs), truncated nanopyramids (TNPs), inverted truncated nanocones (ITNCs), and inverted truncated nanopyramids (ITNPs) are computed using the finite element method (FEM) based commercial COMSOL Multiphysics package. The influence of geometrical dimensions of the investigated nanostructures such as period (P), diameter (D), width (W), filling ratio (FR), bottom W and D (W bot/D bot), and top W and D (W top/D top) on the optical performance are analyzed in detail. Optical short circuit current density (J sc) is computed using the absorption spectra. The results of numerical simulations indicate that InP nanostructures are optically superior to Si nanostructures. In addition to this, the InP TNP generates an optical short circuit current density (J sc) of 34.28 mA cm-2, which is ∼10 mA cm-2 higher than its Si counterpart. The effect of incident angle on the ultimate efficiency of the investigated nanostructures in transverse electric (TE) and transverse magnetic (TM) modes is also explored. Theoretical insights into the design strategies of different nanostructures proposed in this article will act as a benchmark for choosing the device dimensions of appropriate nanostructures for the fabrication of efficient photovoltaic devices.

Features of the development of professional-applied physical qualities in physical education classes in medical institutions of higher education

In this work, we discuss the approaches aimed at improvement of dexterity and endurance, which are the key physical abilities of the physician, as well as their linkages with psychophysiological requirement to a health care professional. We analyze the methods to develop a body and manual dexterity, general speed, strength and other types of endurance. We also emphasize the importance of dexterity and endurance for the physician’s ultimate efficiency, resistance to the unfavorable professional factors and decreasing the risk of cardiovascular diseases.
 Therefore, a doctor of any specialty needs such qualities as the mobility of nervous processes; coordination of movements and muscle efforts; the ability to withstand long-term stress, the body's resistance to adverse environmental influences; emotional stability and will, concentration of attention, self-control, determination, resilience. Doctors of most specialties constantly experience acute and chronic stress states related to their professional activities, the most common of which are the development of emergency conditions in patients, the constant pressure of responsibility for the health and lives of patients, the mismatch of the efforts expended with moral and material rewards, etc.
 Medical education makes high demands on the physical training of future doctors. From the point of view of the peculiarities of the physical activity of the doctor, it makes sense to consider two directions: direct manipulation or operations on the patient's body and purely intellectual activity related to the clarification of the clinical situation, the choice of diagnostic and treatment tactics. However, in everyday activities it is often difficult to separate manual and intellectual activities.

Laminar membranes assembled by ultrathin cobalt-copper oxide nanosheets for nanoconfined catalytic degradation of contaminants

• Nanoconfinement catalysis is implemented within Co-Cu ONS membrane nanochannels. • Co-Cu ONS membrane achieves ∼ 100% removal of organic pollutants within 86 ms. • The degradation rate is 10 3−5 times faster compared with the best state-of-the-art. • Oxygen vacancies facilitate electron transfer between metal cations and PMS. • DFT calculations illustrate the mechanism of nanoconfinement catalysis. Practical applications for the degradation of organic contaminants by conventional batch-mode heterogeneous advanced oxidation processes remain elusive due to mass-transfer limitations of short-lived reactive oxygen species (ROS). Nanoconfinement catalysis has received increasing attention because of enhanced reaction efficiency and mass and electron transfer. Here, we implemented the concept of nanoconfinement catalysis using a two-dimensional membrane. Ultrathin cobalt-copper oxide nanosheets (Co-Cu ONS) rich in active sites and oxygen vacancies were prepared through a facile solution reduction method. The assembled Co-Cu ONS membrane with active sites confined within membrane nanochannels spontaneously activates peroxymonosulfate and facilitates the generation of ROS and the redox cycles of metal cations. Therefore, an ultimate degradation efficiency (∼100%), ultrafast (∼86 ms) decomposition of organic pollutants, and excellent catalytic stability (greater than120 h) were achieved. The degradation rate is 10 3−5 times faster than the best state-of-the-art. This approach offers an attractive alternative for water purification with membrane-based nanoconfinement catalysts.

The nonequilibrium cost of accurate information processing

Accurate information processing is crucial both in technology and in nature. To achieve it, any information processing system needs an initial supply of resources away from thermal equilibrium. Here we establish a fundamental limit on the accuracy achievable with a given amount of nonequilibrium resources. The limit applies to arbitrary information processing tasks and arbitrary information processing systems subject to the laws of quantum mechanics. It is easily computable and is expressed in terms of an entropic quantity, which we name the reverse entropy, associated to a time reversal of the information processing task under consideration. The limit is achievable for all deterministic classical computations and for all their quantum extensions. As an application, we establish the optimal tradeoff between nonequilibrium and accuracy for the fundamental tasks of storing, transmitting, cloning, and erasing information. Our results set a target for the design of new devices approaching the ultimate efficiency limit, and provide a framework for demonstrating thermodynamical advantages of quantum devices over their classical counterparts.

Broadband absorption of modified conical nanowires for photovoltaic applications

In this paper, modified conical nanowires (CNWs) with different top diameters are suggested to break the structure mirror symmetry and increase the light absorption. The proposed arrangement consists of 2 × 2 periodic CNWs with top different conical diameters where the light reflection is reduced and therefore the absorption efficiency is enhanced. The optical characteristics of the suggested CNWs are numerically simulated using three-dimensional 3-D finite-difference time-domain (FDTD) method. The numerical results show that a good coupling of the scattered light is achieved through the proposed NWs with multiple resonant wavelengths. In this context, the Mie resonances are improved and strengthened over a wide range of wavelengths by optimizing the top cone diameters. The reported design offers an ultimate efficiency (η) of 39.8 % and short circuit current density (Jsc) of 35.2 mA/cm2 with an enhancement of 28.8 % compared to the conventional CNWs. When a bottom Si substrate and Ag back reflector are used, the η and Jsc are improved to 42.1 % and 37.4 mA/cm2, respectively. This is owing to the coupling between the supported modes in the NWs and those excited in the Si substrate. The maximum power conversion efficiency (PCE) in the axial junction of the modified CNWs structure is equal to 18 % compared to 15.5 % for the conventional CNWs design with an enhancement of 16 % in the ideal passivation.

Effects of microfracture parameters on adaptive pumping in fractured porous media: Pore-scale simulation

Adaptive pumping, exchanging injection and extraction well locations, has achieved good performance in many subsurface operations such as enhanced oil recovery, CO2 sequestration, and aquifer contaminant remediation. However, the pore-scale flow mechanism behind this phenomenon and the effect of fractures on it are poorly understood. In this study, the phase field method is used to trace the interface evolution in the matrix with different fracture parameters, such as width, length, orientation angle, and tortuosity. The results show that the presence of fractures converts the flow regime from continuous pathway flow (CPF) to ganglion dynamics (GD), which improves the transfer kinetics of the displacing fluid. Fracture width and tortuosity significantly affect the ultimate displacement efficiency in positive pumping, while the orientation angle has the most significant effect in adaptive pumping. The disintegration of the residual displaced fluid into smaller ganglia is the displacement mechanism of adaptive pumping, but it is suppressed in fractured porous media. The adaptive pumping reaches the maximum displacement efficiency when the fracture is vertical to the flow direction, which is 15.12% higher than that of the positive pumping in the non-fractured model. These results can bridge the cognitive gap between micro- and macro-phenomena and guide practical engineering.

Experimental investigation on the anchorage performance of hooked high-strength steel strands for beam-to-column connection

To explore the anchorage performance of hooked steel strands used in the beam-to-column connection of the precast prestressed assembled structural (PPAS) system, considering the influence of the various research variables, such as anchorage length and the length of the vertical segment of the steel strand, 16 specimens were designed and tested under the pull-out loading. The failure modes, pull-out load-slip curves, peak point loads, and the corresponding slips of the tested specimens were obtained accordingly. Besides, by means of portable X-ray detection technology, the shape evolution of hooked steel strands in the concrete columns under various pull-out loads were imaged and compared, and the anchorage failure mechanism of hooked steel strands was further clarified. The test results demonstrated that three failure modes were observed in all test specimens. Besides, the hooked steel strands can significantly improve its ultimate anchorage capacity and material strength utilization efficiency. When the anchorage length is not less than 500 mm, and the length of the vertical segment is 5d, 10d and 15d, the conical fracture failure of the steel strand always occurs in the test specimens, and the material strength utilization efficiency is always not less than 90 %, far higher than that of the straight steel strands. In addition, the relative slip at the loaded end is obviously related to the anchorage parameters of the steel strands. In details, whether the length of the vertical segment is 5d, 10d or 15d, the relative slip of the hooked steel strand is significantly lower than that of the straight steel strand, which is strongly related to the unique anchoring mechanism of hooked steel strand. However, the necessary anchorage length is needed for hooked steel strands to achieve the ideal anchorage effect, which should generally not be less than 500 mm.

Quantum Dot to Nanorod Transition for Efficient White-Light-Emitting Diodes with Suppressed Absorption Losses

Colloidal nanocrystals have great potential for next-generation solid-state lighting due to their outstanding emission and absorption tunability via size and morphology, narrow emission linewidth, and high photoluminescence quantum yield (PLQY). However, the losses due to self- and interabsorption among multitudes of nanocrystals significantly decrease external quantum yield levels of light-emitting diodes (LEDs). Here, we demonstrate efficient white LEDs via CdSe/CdS dot to “dot-in-rod” transition that enabled a large Stokes shift of 780 meV and significantly reduced absorption losses when used in conjunction with near-unity PLQY ZnCdSe/ZnSe quantum dots (QDs) emitting at the green spectral range. The optimized incorporation of nanocrystals in a liquid state led to the white LEDs with an ultimate external quantum efficiency (EQE) of 42.9%, with a net increase of EQE of 10.3% in comparison with white LEDs using CdSe/CdS dots. Therefore, combinations of nanocrystals with different nanomorphologies hold high promise for efficient white LEDs.

Measuring technological innovation efficiency using interval type-2 fuzzy super-efficiency slack-based measure approach

As an important leading industry in China’s economy, the high-tech industry needs to systematically analyze technological innovation activities, thereby measuring the technological innovation efficiency and further improving sustainable development. The high-tech industry in different provinces benefits from individual policies due to their geographical locations. However, since the intensity of policy implementation in the technological innovation activities of the provincial high-tech industry is qualitative information, which is difficult to be expressed by quantitative data and rarely considered in the efficiency assessment. Therefore, this study adopts interval type-2 fuzzy sets to characterize the uncertain qualitative information and constructs an interval type-2 fuzzy evaluation method to measure the technological innovation efficiency of China’s high-tech industry. More specifically, considering the handling of undesirable outputs and the ranking of multiple efficient decision-making units, the super-efficiency slack-based measure (SBM)-Data envelopment analysis (DEA) method has been selected as the basic evaluation model. Then, the super-efficiency SBM-DEA model has been extended into an interval type-2 evaluation approach by considering the uncertain variables. Moreover, the α-cuts and best-and-worst methods are introduced to conduct the decomposition of the proposed evaluation model and aggregate the ultimate efficiency. Finally, a comparative analysis of technological innovation efficiency in the regional high-tech industry has been performed to validate the applicability of the proposed model.

Does non-reciprocity break the Shockley–Queisser limit in single-junction solar cells?

The efficiency of single-junction solar cells is bounded by the Shockley–Queisser limit of 41%. However, standard derivation for this limit constrains the system to be reciprocal, and what non-reciprocity can bring for single-junction solar cells remains yet to be clarified. Here, we prove that even with non-reciprocity, the ultimate efficiency of single-junction solar cells is still subject to the Shockley–Queisser limit. We show that the Shockley–Queisser limit does not rely on the detailed balance, but rather is a consequence of the integrated balance between the absorption and emission processes, as required by the second law of thermodynamics.

Fundamental efficiency bound for quantum coherent energy transfer in nanophotonics.

We derive a unified quantum theory of coherent and incoherent energy transfer between two atoms (donor and acceptor) valid in arbitrary Markovian nanophotonic environments. Our theory predicts a fundamental bound η m a x =γ a γ d+γ a for energy transfer efficiency arising from the spontaneous emission rates γd and γa of the donor and acceptor. We propose the control of the acceptor spontaneous emission rate as a new design principle for enhancing energy transfer efficiency. We predict an experiment using mirrors to enhance the efficiency bound by exploiting the dipole orientations of the donor and acceptor. Of fundamental interest, we show that while quantum coherence implies the ultimate efficiency bound has been reached, reaching the ultimate efficiency does not require quantum coherence. Our work paves the way towards nanophotonic analogues of efficiency-enhancing environments known in quantum biological systems.

A Review of China's Financial Markets

The fast growth of China's economy has brought it not only to the center of the global economy but also to a transition point in its growth model, a transition from scale to efficiency, speed to sustainability, input driven to innovation led. How its financial markets can drive this new growth model and facilitate the transition are pressing challenges, for China and for the world. We provide a comprehensive review of China's financial markets, including government bonds, corporate/credit bonds, stocks, asset-backed securities, financial derivatives, investment management, and currency, focusing on their growth paths, distinct characteristics, and unique opportunities. Despite fast expansion at times, their development is often lagging behind market needs, uneven over time, and unbalanced across markets. This developmental pattern is driven mostly by the government's immediate policy objectives rather than by the markets' ultimate efficiency in serving their key functions, including liquidity provision, price discovery, and risk allocation.