Tandem Structure Research Articles

Probing fluorescence resonance energy transfer and hole transfer in organic solar cells using a tandem structure

The energy transfer and hole transfer processes in thin films and devices were probed using a tandem structure composed of donors/hole materials/acceptors.

Organic photodetectors: materials, device, and challenges

Organic photodetectors (OPDs) are increasingly important in photoelectric detection; here is an overview of OPDs about the performance metrics, the development possibilities of materials and tandem structures, and the challenges in applications.

Effect and optimization of the Zn3P2 back surface field on the efficiency of CZTS/CZTSSe tandem solar cell: a computational approach

Copper zinc tin sulfide (CZTS) and copper zinc tin sulfo selenide (CZTSSe) kesterite minerals are nontoxic and abundant in the earth with the promise of cost-effective photovoltaic applications. This study explains a tandem solar cell made of kesterite materials that can capture sunlight over a broad spectrum. The proposed tandem structure comprises a wide bandgap CZTS thin-film upper subcell and an underlying narrow bandgap CZTSSe-based lower subcell. The upper and lower subcells are simulated using solar cell capacitance simulator-one dimension and validated against the experimental results to determine the viability of the proposed tandem design. Additionally, the performance of both subcells is evaluated for tandem configuration by adding a back surface field layer, a modification of the back contact, testing at different thicknesses, and doping of both subcell absorber layers. As a result, optimizing both subcells improved tandem solar cell open-circuit voltage (V oc) to a maximum of 1.5 V, which led to an efficiency of 23.99% at the current matching condition. Furthermore, how light radiation power and temperature variations impact the proposed solar cell performance is being investigated. This study provides significant insights into efficient tandem solar cell design and manufacture.

Tandem repeats structure of gel-forming mucin domains could be revealed by SMRT sequencing data

Mucins are large glycoproteins that cover and protect epithelial surface of the body. Mucin domains of gel-forming mucins are rich in proline, threonine, and serine that are heavily glycosylated. These domains show great complexity with tandem repeats, thus make it difficult to study the sequences. With the coming of single molecule real-time (SMRT) sequencing technologies, we manage to present sequence structure of mucin domains via SMRT long reads for gel-forming mucins MUC2, MUC5AC, MUC5B and MUC6. Our study shows that for different individuals, single nucleotide polymorphisms could be found in mucin domains of MUC2, MUC5AC, MUC5B and MUC6, while different number of tandem repeats could be found in mucin domains of MUC2 and MUC6. Furthermore, we get the sequence of MUC2, MUC5AC, and MUC5B mucin domain in a Chinese individual for each nucleotide at accuracy of possibly 99.98–99.99%, 99.93–99.99%, and 99.76–99.99%, respectively. We report a new method to obtain DNA sequence of gel-forming mucin domains. This method will provided new insights on getting the sequence for Tandem Repeat parts which locate in coding region. With the sequences we obtained through this method, we can give more information for people to study the sequences of gel-forming mucin domains.

Bifacial all-perovskite tandem solar cells.

The efficiency of all-perovskite tandem devices falls far below theoretical efficiency limits, mainly because a widening bandgap fails to increase open-circuit voltage. We report on a bifacial all-perovskite tandem structures with an equivalent efficiency of 29.3% under back-to-front irradiance ratio of 30. This increases energy yield and reduces the required bandgap of a wide-bandgap cell. Open-circuit voltage deficit is therefore minimized, although its performance under only front irradiance is not ideal. The bifacial device needs a sputtered rear transparent electrode, which could reduce photon path length and deteriorate stability of Pb-Sn perovskites. Embedding a light-scattering micrometer-sized particle layer into perovskite to trap light, effectively increases absorptance by 5 to 15% in the infrared region. Using a nonacidic hole transport layer markedly stabilizes the hole-extraction interface by avoiding proton-accelerated formation of iodine. These two strategies together increase efficiency of semitransparent Pb-Sn cells from 15.6 to 19.4%, enabling fabrication of efficient bifacial all-perovskite tandem devices.

Identification of Novel tet(X3) Variants Resistant To Tigecycline in Acinetobacter Species.

The emergence of the tet(X) gene is a severe challenge to global public health security, as clinical tigecycline resistance shows a rapidly rising trend. In this research, we identified two tigecycline-resistant Acinetobacter sp. strains containing seven novel tet(X3) variants recovered from fecal samples from Chinese farms. The seven Tet(X3) variants showed 15.4% to 99.7% amino acid identity with Tet(X3). By expressing tet(X3.7) and tet(X3.9), the tigecycline MIC values for Escherichia coli JM109 increased 64-fold (from 0.13 to 8 mg/L). However, the other tet(X3) variants did not have a significant change in the MIC of tigecycline. We found that the 26th amino acid site of Tet(X3.7) changed from proline to serine, and the 25th amino acid site of Tet(X3.9) changed from glycine to alanine, which reduced the MIC of tigecycline by 2-fold [the MIC of tet(X3) to tigecycline was 16 mg/L] but did not affect its expression to tigecycline. The tet(X3) variants surrounded by mobile genetic elements appeared in the structure of gene clusters with tandem repeat sequences and were adjacent to the site-specific recombinase-encoding gene xerD. Therefore, there is a risk of horizontal transfer of resistant genes. Our study reports seven novel tet(X3) variants; the continuing emergence of tigecycline variants makes continuous monitoring of resistance to tigecycline even more critical. IMPORTANCE Although it is illegal to use tigecycline and carbapenems to treat bacterial infections in animals, we can still isolate bacteria containing both mobile resistance genes from animals, and tet(X) is currently an essential factor in degrading tigecycline. Here, we characterized two multidrug-resistant Acinetobacter sp. strains that contained vital resistance genes, such as sul2, a blaOXA-164-like gene, floR, tetM, and multiple novel tet(X3) variants with different tandem structures. It is of paramount significance that their mechanism may transfer to other Gram-negative pathogens, even if their tandem structures have no cumulative effect on tigecycline resistance.

Effect of degrees of structural freedom on the flow-induced vibrations of isolated and tandem cylindrical structures

This study aims to numerically investigate the influence of degrees of structural freedom on the flow-induced vibration characteristics of an isolated and tandem cylindrical structures at low Reynolds number. Both the single and tandem cylinders underwent transverse-only (1-DoF) and combined streamwise and transverse (2-DoF) vibrations which are characterized by the mass–spring system. A fluid–structure interaction scheme is formulated using the split-forcing lattice Boltzmann equation for the fluid domain in combination with an immersed boundary solver and equations of rigid body motion for the structural part. The dynamic response of an isolated and tandem structures computed for 1- and 2-DoF cases are similar regarding the lock-in phenomenon and hydrodynamic forces at a relatively large mass ratio. The comparison of vorticity field suggests that an additional degree of freedom has no significant effect on the vortex shedding pattern. Furthermore, in the presence of another identical structure placed in the upstream direction, the downstream structure oscillates with higher amplitudes.

Optical design and optimization of BP/c-Si tandem solar cells

Black phosphorus (BP), widely studied in nanophotonics, has shown great potential applications in the field of thin film solar cells due to the wide absorption wavelength range and the tunable band-gap. Here, a tandem solar cell with BP and crystalline silicon (c-Si) as top and bottom active layer are proposed. Two types of optical design strategies such as one dimensional photonic crystal interlayers and top nanopyramid antireflective layer are employed to optimize the BP/c-Si tandem cell device structure to enhance the light absorption. Simulation results show that the one dimensional photonic crystal interlayers significantly enhance the light absorption in the tandem solar cell while nanopyramid antireflective layer hardly works. With optimized structure parameters, a maximum short-circuit current of 18.50 mA/cm2 for BP/c-Si tandem solar cell with one dimensional photonic crystal interlayers has been achieved which is enhanced by 19.4% compare to that of the counterpart without interlayers.

A BAK subdomain that binds mitochondrial lipids selectively and releases cytochrome C.

How BAK and BAX induce mitochondrial outer membrane (MOM) permeabilization (MOMP) during apoptosis is incompletely understood. Here we have used molecular dynamics simulations, surface plasmon resonance, and assays for membrane permeabilization in vitro and in vivo to assess the structure and function of selected BAK subdomains and their derivatives. Results of these studies demonstrate that BAK helical regions α5 and α6 bind the MOM lipid cardiolipin. While individual peptides corresponding to these helical regions lack the full biological activity of BAK, tandem peptides corresponding to α4-α5, α5-α6, or α6-α7/8 can localize exogenous proteins to mitochondria, permeabilize liposomes composed of MOM lipids, and cause MOMP in the absence of the remainder of the BAK protein. Importantly, the ability of these tandem helices to induce MOMP under cell-free conditions is diminished by mutations that disrupt the U-shaped helix-turn-helix structure of the tandem peptides or decrease their lipid binding. Likewise, BAK-induced apoptosis in intact cells is diminished by CLS1 gene interruption, which decreases mitochondrial cardiolipin content, or by BAK mutations that disrupt the U-shaped tandem peptide structure or diminish lipid binding. Collectively, these results suggest that BAK structural rearrangements during apoptosis might mobilize helices involved in specific protein-lipid interactions that are critical for MOMP.

Performance analysis of near-field tandem thermophotovoltaic systems based on radiative absorption distribution

Fluctuational electrodynamics and minority carrier diffusion equations are applied to evaluate the electric power output of a near-field tandem thermophotovoltaic (TPV) system with a bulk tungsten emitter (at 1500 K) and InGaSb/InAs tandem cells (at 300 K). We give evidence of the superiority of the tandem TPV system over the single-junction TPV system in the near-field regime because a tandem structure can harvest useful photons in a wider spectral range. It is also found that in comparison with the system with a bulk tungsten emitter, the practically achievable indium‑tin‑oxide (ITO) emitter and multilayer emitter could enhance the electricity output by a factor of 1.7 and 2.9 as a result of the supported surface plasmon resonances and hyperbolic modes, respectively. The conversion efficiency of the ITO emitter is 6% higher due to the suppression of the surface recombination loss, but the efficiency of the multilayer emitter is even 15% lower because of the heavy bulk recombination loss. These results highlight the possibilities to enhance the performance of the near-field tandem TPV systems via optimizing the radiative absorption distribution in the tandem cells, which is paramount important for the design and improvement of near-field tandem TPV systems.

Calculation of Mass Spectra with the QCxMS Method for Negatively and Multiply Charged Molecules.

Analysis and validation of a mass spectrometry (MS) experiment are usually performed by comparison to reference spectra. However, if references are missing, measured spectra cannot be properly matched. To close this gap, the Quantum Chemical Mass Spectrometry (QCxMS) program has been developed. It enables fully automatic calculations of electron ionization (EI) and positive ion collision-induced dissociation (CID) mass spectra of singly charged molecular ions. In this work, the extension to negative and multiple ion charge for the CID run mode is presented. QCxMS is now capable of calculating structures carrying any charge, without the need for pretabulated fragmentation pathways or machine learning of database spectra. Mass spectra of four single negatively charged and two multiple positively charged organic ions with molecular sizes from 12 to 92 atoms were computed and compared to reference spectra. The underlying Born-Oppenheimer molecular dynamics (MD) calculations were conducted using the semiempirical quantum mechanical GFN2-xTB method, while for some small molecules, ab initio DFT-based MD simulations were performed. Detailed insights into the fragmentation pathways were gained, and the effects of the computed charge assignments on the resulting spectrum are discussed. Especially for the negative ion mode, the influence of the deprotonation site to create the anion was found to be substantial. Doubly charged fragments could successfully be calculated fully automatically for the first time, while higher charged structures introduced severe assignment problems. Overall, this extension of the QCxMS program further enhances its applicability and underlines its value as a sophisticated toolkit for CID-based tandem MS structure elucidation.

Mechanical properties of negative Poisson's ratio metamaterial units and honeycomb structures with cosine-like re-entrant structure

Aiming at the problems of stress concentration and negative Poisson's ratio in the deformation process of the re-entrant structure, a cosine-shaped re-entrant structure negative Poisson's ratio metamaterial is proposed in this paper. By optimizing the inclined beams in the re-entrant structural elements into single cosine, tandem cosine and multiple cosine buckling beams, different configurations of improved re-entrant structural elements are designed. Finite element modeling and quasi-static compression simulations and experiments are carried out for single and periodically arranged re-entrant structures. The results show that the comprehensive stress of the single cosine structure and the tandem cosine structure are reduced by 18.7% and 58%, respectively, and the maximum stress can be reduced by 6.7% and 5.2%, respectively. In addition, the negative Poisson's ratio of metamaterial with a single cosine re-entrant structure is increased by 14% compared with that before the improvement.

Loop CD20/CD19 CAR-T cells eradicate B-cell malignancies efficiently.

CD19 chimeric antigen receptor (CAR) T cells have shown robust efficacy in relapsed and refractory acute lymphoblastic leukemia (R/R ALL), but compromising result in chronic lymphoblastic leukemia (CLL) and non-Hodgkin's lymphoma (NHL). CD19 relapse and the lack of CAR-T cell persistence which result in treatment failure are considerable obstacles to overcome. CAR-T targeting CD20 is an option for salvaging CD19 CAR-T failure. Previous studies have established variant structures of bispecific CAR-T which could avoid antigen-loss and immune escape. Here, we constructed tandem and loop CAR structures targeting both CD19 and CD20 antigen. Bispecific CAR-T cells could eliminate either CD19 or CD20 negative lymphoma cells, suggesting they exhibited dual antigen targeting of CD19 and CD20. By comparing the efficiency of four bispecific CAR modified T cells, it was found that loop2019 CAR was the best structure among them to eradicate lymphoma cell lines and patients' primary lymphoma or CLL cells in a very low dose in vitro and prolong the survival time dramatically in lymphoma xenograft mice model. These data highlighted the potential of loop2019 CAR-T in clinical treatment.

3R-TaS2as an Intercalation-Dependent Electrified Interface for Hydrogen Reduction and Oxidation Reactions

Hydrogen technology, as a future breakthrough for the energy industry, has been defined as an environmentally friendly, renewable, and high-power energy carrier. The green production of hydrogen, which mainly relies on electrocatalysts, is limited by the high cost and/or the performance of the catalytic system. Recently, studies have been conducted in search of bifunctional electrocatalysts accelerating both the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR). Herein, we report the investigation of the high efficiency bifunctional electrocatalyst TaS2 for both the HER and the HOR along with the asymmetric effect of inhibition by organic intercalation. The linear organic agent, to boost the electron donor property and to ease the process of intercalation, provides a higher interlayer gap in the tandem structure of utilized nanosheets. XRD and XPS data reveal an increase in the interlayer distance of 22%. The HER and the HOR were characterized in a Pt group metal-free electrochemical system. The pristine sample shows a low overpotential of −0.016 V at the onset. The intercalated sample demonstrates a large shift in its performance for the HER. It is revealed that the intercalation is a potential key strategy for tuning the performance of this family of catalysts. The inhibition of the HER by intercalation is considered as the increase in the operational window of a water-based electrolyte on a negative electrode, which is relevant to technologies of electrochemical energy storage.

Improvement Strategies for Stability and Efficiency of Perovskite Solar Cells.

Recently, perovskites have garnered great attention owing to their outstanding characteristics, such as tunable bandgap, rapid absorption reaction, low cost and solution-based processing, leading to the development of high-quality and low-cost photovoltaic devices. However, the key challenges, such as stability, large-area processing, and toxicity, hinder the commercialization of perovskite solar cells (PSCs). In recent years, several studies have been carried out to overcome these issues and realize the commercialization of PSCs. Herein, the stability and photovoltaic efficiency improvement strategies of perovskite solar cells are briefly summarized from several directions, such as precursor doping, selection of hole/electron transport layer, tandem solar cell structure, and graphene-based PSCs. According to reference and analysis, we present our perspective on the future research directions and challenges of PSCs.

Enhanced nonreciprocal light propagation based on epsilon-near-zero medium in the visible regime

We have experimentally demonstrated the nonreciprocal light propagation based on the axially asymmetric nonlinear absorption in the epsilon-near-zero (ENZ) media titanium nitride (TiN) nanosheets and C60 arranged in tandem in the visible regime. TiN nanosheets have been prepared and characterized to show broadband and ultrafast nonlinear optical response with the maximum nonlinear absorption coefficient about −5.05×10−8 m/W at its ENZ wavelength, which is about ten times larger than that at 400 nm. With the enhanced nonlinear absorption of TiN nanosheets, a passive photonic diode fabricated with TiN-C60 in a tandem structure shows enhanced nonreciprocal transmission of femtosecond laser pulses with a nonreciprocity factor of 9.5 dB at the ENZ wavelength. The results show the potential applications of TiN nanosheets in ultracompact, polarization-independent, and physiochemically stable nonreciprocal light propagation and may pave way for the application of broadband ENZ-based all-optical devices.

Effect of an ultra-thin 2D transport layer on eco-friendly Perovskite/CIGS tandem solar cell: A numerical study

The major limitation of two-terminal (2T) tandem configuration is its lower operating current density, as electrically, the higher and lower bandgap cells are connected in series. In such an arrangement, the output of the tandem cell is constrained by the cell that produces the smallest photocurrent. To mitigate this issue, we have proposed a 2T lead-free Perovskite/CIGS tandem structure using ultra-thin transport materials with which high photocurrent and higher efficiency have been achieved. Cesium tin germanium tri-iodide (CsSn0.5Ge0.5I3), a lead–free perovskite with a bandgap of 1.5 eV and copper indium gallium selenide (CIGS) with a bandgap of 1.1 eV, have been utilised as an active layers for the top and bottom sub cells, respectively. These sub cells have been first evaluated in a single junction architecture under standard solar spectrum (AM 1.5 spectrum), yielding a power conversion efficiency (PCE) of 25.72% and 26.20%, respectively. They are then investigated for tandem configuration for which the current matching point is obtained by changing the thickness of the top and bottom active layers. This requirement is met when the top and bottom sub cells in the tandem cell have optimum thicknesses of 298.15 nm and 1000 nm, respectively. Finally, to evaluate tandem performance parameters, the top sub-cell is illuminated under the standard AM 1.5 spectrum, keeping its active layer thickness at 298.15 nm, while the performance parameter of bottom sub-cell are computed under the calculated filtered spectrum. With an improved open circuit voltage (VOC) of 1.94 V, the proposed tandem structure attained a high efficiency of 34.87%.

Simulation Study on Broadband Light Harvesting Properties of Aluminium Nanosphere and Silicon Nanopillar Arrays based Tandem Structure

Simulation Study on Broadband Light Harvesting Properties of Aluminium Nanosphere and Silicon Nanopillar Arrays based Tandem Structure

Accurate measurement of microsatellite length by disrupting its tandem repeat structure.

Tandem repeats of simple sequence motifs, also known as microsatellites, are abundant in the genome. Because their repeat structure makes replication error-prone, variant microsatellite lengths are often generated during germline and other somatic expansions. As such, microsatellite length variations can serve as markers for cancer. However, accurate error-free measurement of microsatellite lengths is difficult with current methods precisely because of this high error rate during amplification. We have solved this problem by using partial mutagenesis to disrupt enough of the repeat structure of initial templates so that their sequence lengths replicate faithfully. In this work, we use bisulfite mutagenesis to convert a C to a U, later read as T. Compared to untreated templates, we achieve three orders of magnitude reduction in the error rate per round of replication. By requiring agreement from two independent first copies of an initial template, we reach error rates below one in a million. We apply this method to a thousand microsatellite loci from the human genome, revealing microsatellite length distributions not observable without mutagenesis.

Disentangling the Orientations of Spectrally Overlapping Transition Dipoles in Dense Dye Layers

The transition dipole orientations of dye assemblies in heterostructures have a crucial impact on the efficiency of novel optoelectronic devices such as organic thin-film transistors and light-emitting diodes. These devices are frequently based on heterojunctions and tandem structures featuring multiple optical transitions. Precise knowledge of preferred orientations, spatial order, and spatial variations is highly relevant. We present a fast and universal large-area screening method to determine the transition dipole orientations in dye assemblies with diffraction-limited spatial resolution. Moreover, our hyperspectral imaging approach disentangles the orientations of different chromophores. As a demonstration, we apply our technique to dye monolayers with two optical transitions sandwiched between two ultrathin silicate nanosheets. A comprehensive model for dipole orientation distributions in monolayers reveals a long-range orientational order and a strong correlation between the two transitions.