Current Matching Research Articles

Comprehensive device simulation of 23.36% efficient two-terminal perovskite-PbS CQD tandem solar cell for low-cost applications

The major losses that limit the efficiency of a single-junction solar cell are thermalization loss and transmission loss. Thus, to efficiently utilize the full solar spectrum and to mitigate these losses, tandem solar cells (TSC) have significantly impacted the photovoltaic (PV) landscape. In this context, the research on perovskite/silicon tandems is currently dominating the research community. The stability improvements of perovskite materials and mature fabrication techniques of silicon have underpinned the rapid progress of perovskite/silicon TSC. However, the low absorption coefficient and high module cost of the silicon are the tailbacks for the mass production of perovskite/silicon TSCs. Therefore, PV technology demands to explore some new materials other than Si to be used as absorber layer in the bottom cell. Thus, here in this work, to mitigate the aforementioned losses and to reduce cost, a 23.36% efficient two-terminal perovskite-PbS CQD monolithic tandem solar cell has been designed through comprehensive device simulations. Before analyzing the performance of the proposed TSC, the performance of perovskite top cells has been optimized in terms of variation in optical properties, thickness, and interface defect density under standalone conditions. Thereafter, filtered spectrum and associated integrated filtered power by the top cell at different perovskite thickness from 50 to 500 nm is obtained to conceive the presence of the top cell above the bottom cell with different perovskite thickness. The current matching by concurrently varying the thickness of both the top and bottom subcell has also been done to obtain the maximum deliverable tandem JSC for the device under consideration. The top/bottom subcell with current matched JSC of 16.68 mA cm−2/16.62 mA cm−2 showed the conversion efficiency of 14.60%/9.07% under tandem configuration with an optimized thickness of 143 nm/470 nm, where the top cell is simulated under AM1.5G spectrum, and bottom cell is exposed to the spectrum filtered by 143 nm thick top cell. Further, the voltages at equal current points are added together to generate tandem J–V characteristics. This work concludes a 23.36% efficient perovskite-PbS CQD tandem design with 1.79 V (VOC), 16.67 mA cm−2 (JSC) and 78.3% (FF). The perovskite-PbS CQD tandem device proposed in this work may pave the way for the development of high-efficiency tandem solar cells for low-cost applications.

Equivalent circuit and fundamental limit of multi-stage infrared photodetectors

Based on an equivalent circuit model, a signal current in a multi-stage infrared (IR) photodetector is derived and used to discover a meaningful relation among quantum efficiency, collection efficiency, and particle conversion efficiency. Based on such a relation, it is demonstrated theoretically that the ultimate detectivities in multi-stage interband cascade infrared photodetectors (ICIPs) with identical discrete absorbers are the same as that in a conventional single-absorber detector in the limit of perfect collection (i.e., independent of the number of cascade stages) but higher than that in the single-stage detector with a finite diffusion length. Detailed derivations and calculations, along with relevant discussion, are provided to show how ICIPs are optimized for maximizing the detectivity and to understand the underlying physics. Multi-stage ICIPs with identical discrete absorbers are robust and durable against structural variations without being restricted by current matching and, therefore, are of more significance for practical applications such as those that require high-speed response or circumventing the diffusion length limitation. The results obtained for ICIPs with identical discrete absorbers can also be applied for quantum cascade detectors and photovoltaic quantum well infrared photodetectors. The results and insights gained from this work will further improve the understanding of multi-stage IR photodetectors and generate increased interest in the development of ICIPs and related devices for useful applications.

Strategic investment decisions in multi-stage contests with heterogeneous players

When heterogeneous players make strategic investment decisions in multi-stage contests, they might conserve resources in a current contest to spend more in a subsequent contest, if the degree of heterogeneity in the current (subsequent) contest is sufficiently large (small). We confirm these predictions using data from German professional soccer, in which players are subject to a one-match ban if they accumulate five yellow cards. Players with four yellow cards facing the risk of being suspended for the next match are (i) less likely to be fielded when the heterogeneity in the current match increases and (ii) more likely to receive a fifth yellow card in the current match when heterogeneity in the next match increases or heterogeneity in the next match but one (when they return from their ban) decreases.

A study on the influence of the albedo spectrum on the bifacial GaAs/c-Si heterojunction tandem solar cell using computer modelling

Recently, III-V/c-Si heterojunction (c-Si HJ) tandem solar cells received considerable attention owing to their high conversion efficiency. In a tandem configuration, current matching has a significant impact on conversion efficiency. Specifically, in the two-terminal tandem structure, the sub-cell with the lowest current density (Jsc) dominates the Jsc of the tandem cell, which in turn, dominates the overall conversion efficiency of the tandem device. Meanwhile, in a four-terminal tandem structure, although the current matching condition is not mandatory, an efficient light distribution is necessary to achieve high efficiency in each sub-cell, which in turn results in a high efficiency of the tandem cell. Herein, we propose two- and four-terminal GaAs/c-Si HJ tandem solar cells using effective albedo reflections (RA) to overcome the aforementioned limitations. As RA increased, the current density of the c-Si HJ solar cells increased from 3.07 mA/cm2 (RA = 10%) to 39.90 mA/cm2 (RA = 100%) on the rear side of the cell, thereby, overcaming the existing current density limit. In addition, we investigated the tandem structures via simulation to provide a practical direction for achieving high efficiency. Finally, normalised outputs of 40.00% and 40.31% were achieved for the two-terminal and four-terminal GaAs/c-Si HJ bifacial tandem solar cells, respectively, with a real-life albedo from common ground surfaces, such as sand.

Governing the Ni content and size of 2D layered C/Ni nanoparticle composites for enhanced electromagnetic wave absorption

The size and dispersity of magnetic metal absorbents need to be controlled for the inhibition of the eddy current and the enhancement of electromagnetic wave absorption performance (EMWAP). Herein, layered C/Ni nanoparticle (NP) composites were developed as an excellent electromagnetic wave absorbent via the size and dispersity control. The synthesis of layered C/Ni NP composites was achieved via a simple one-step calcination process. The amount of nickel acetate (n) and calcination temperature (Tc) were changed to not only control the diameter, content, and dispersity of Ni nanoparticles, but also adjust the electric/magnetic properties and EMWAP of layered C/Ni NP composites. The superior EMWAP was obtained at n = 3.99 mmol and Tc = 600 °C with high assimilation (−39.46 dB), thin thickness (2.3 mm), and broad bandwidth (9.68 GHz) in a low loading rate (25 wt%). Our results suggest that excellent EMWAPs relies on the cooperation of multiple polarization loss, multiple resonances, eddy current loss, electric/magnetic coupling, and good impedance matching. The synthetic method adopted in this work has advantages of simple operation, low cost, and high yield, which is recommended to other 2D materials.

Modeling and simulation of bifacial perovskite/PERT-silicon tandem solar cells

In this paper, we physically modeled a bifacial perovskite/PERT-silicon tandem solar cells for the first time using Silvaco technology computer-aided design simulator (TCAD). The cell model was calibrated with the reported experimental data of perovskite solar cell (PSC) and PERT-silicon solar cell. The effects of perovskite thickness (tpvk) and perovskite bandgap were investigated on the performance of bifacial tandem solar cells under different albedo. The simulation results predict that the optimum tpvk increases with albedo intensities because a thicker perovskite layer is needed to facilitate current matching for high albedos. Moreover, the tpvk tolerance for a high-efficiency bifacial tandem solar cell increases with albedo. The simulation results reveal an efficiency over 31.9% for 0.45–1 μm of tpvk with 1.65–1.75 eV perovskite bandgap for a bifacial tandem cell under 30% albedo. Additionally, compared to the monofacial cell, the tandem design shows an enhancement of about 30% at the spectral albedo level of common grounds like concrete. The simulation and analysis presented in this work can help optimize perovskite/silicon tandem cell manufacturing to achieve higher power conversion efficiencies.

Point2CN: Progressive two-view correspondence learning via information fusion

Finding reliable correspondences between two views is crucial for solving feature matching based tasks. Given initial correspondences of feature points, recent researches propose an end-to-end permutation-equivariant classification network based on the multi-layer perceptron to label each initial correspondence as inlier or outlier and then regress the camera pose. However, they utilize the PointCN block as network backbones, which cannot gather sufficient contextual information for network learning due to the single sequential structure. In this paper, we propose a new modified block, called Point2CN block, via multi-subsets information fusion, for feature matching. Specifically, the Point2CN block exploits a hierarchical residual-like manner to connect feature map subsets, and then fuses their mutual information by the weighted addition operation to improve feature representation capacity. The simple yet effective Point2CN block can significantly improve the performance of current learning-based feature matching methods with the negligible increase of network parameters. The Point2CN block also will not bring expensive computational overheads since it only involves some novel information fusion operations. Extensive experiments over different challenging datasets on the task of outlier removal and camera pose estimation consistently demonstrate that our Point2CN block is able to gain outstanding performance improvements compared with the existing state-of-the-art methods.

Compact TSA with Anti-Spiral Shape and Lumped Resistors for UWB Applications.

A novel compact tapered-slot-fed antenna (TSA) with anti-spiral shape and lumped resistors is presented for ultra-wideband (UWB) applications. Unique coplanar waveguide (CPW) to coplanar strip (CPS) feeding structure and exponential slot are designed to ensure the continuous current propagation and good impedance matching. With a pair of anti-spiral-shaped structure loadings at the end of the antenna, the radiation performance in lower operating band can be enhanced obviously. The typical resistor loading technique is applied to improve the time domain characteristics and expand the bandwidth. The fabricated prototype of this proposed antenna with a size of 53 × 63.5 mm2 was measured to confirm simulated results. The proposed antenna has S11 less than −10 dB in the range of 1.2–9.8 GHz, and the group delay result is only 0.4 ns. These findings indicate the proposed antenna can be taken as a promising candidate in UWB communication field.

Inefficiencies in Residency Matching Associated with Gale–Shapley Algorithms

Abstract Objective This study aimed to investigate emerging trends and increasing costs in the National Residency Matching Program (NRMP) and San Francisco Residency and Fellowship Match Services (SF Match) associated with the current applicant/program Gale–Shapley-type matching algorithms. Design A longitudinal observational study of behavioral trends in national residency matching systems with modeling of match results with alternative parameters. Patients and Methods We analyzed publicly available data from the SF Match and NRMP websites from 1985 to 2020 for trends in the total number of applicants and available positions, as well the average number of applications and interviews per applicant for multiple specialties. To understand these trends and the algorithms' effect on the residency programs and applicants, we analyzed anonymized rank list and match data for ophthalmology from the SF Match between 2011 and 2019. Match results using current match parameters, as well as under conditions in which applicant and/or program rank lists were truncated with finalized rank lists, were analyzed. Results Both the number of applications and length of programs' rank lists have increased steadily throughout residency programs, particularly those with competitive specialties. Capping student rank lists at seven programs, or less than 80% of the average 8.9 programs currently ranked, results in a 0.71% decrease in the total number of positions filled. Similarly, capping program rank lists at seven applicants per spot, or less than 60% of the average 11.5 applicants ranked per spot, results in a 5% decrease in the total number of positions filled. Conclusion While the number of ophthalmology positions in the United States has increased only modestly, the number of applications under consideration has increased substantially over the past two decades. The current study suggests that both programs and applicants rank more choices than are required for a nearly complete and stable match, creating excess cost and work for both applicants and programs. “Stable-marriage” type algorithms induce applicants and programs to rank as many counterparties as possible to maximize individual chances of optimizing the match.

Matching Subscription Over Geo-Textual Streams from IoT via Social-Aware Clustering and Apache Flink

Current location-based services (LBS) continuously generate a massive amount of geo-message streams. The cluster-based subscription matching method is an effective means to feed subscribers with related geo-messages from geo-message streaming. However, current cluster-based subscription matching methods only consider the spatial relationship and textual relationship and ignore users’ social relationship. As a result, the matching results may not completely satisfy the requirements of users. In this paper, we proposed a social-aware subscription matching method by taking spatial, textual, and social factors into consideration. Then, we used a cache strategy and a Flink-based acceleration process to reduce the extra time overhead caused by computing the social relationships. A set of extensive experiments have been conducted on a real dataset. The experimental results indicate that our method improves the recall of matching results. Besides, the Flink-based acceleration process with caching can speed up the subscription matching process by a ratio of up to 3.299 compared with the state-of-the-art.

Analysis of corner kicks at the FIFA Women’s World Cup 2019 in relation to match status and team quality

ABSTRACT This study analysed the characteristics of 476 corner kicks taken during 52 matches at the FIFA women’s World Cup 2019. The effect of current match status/team quality was examined, and the corner characteristics associated with the 17 goals scored from corners (3.6%) and 93 shots on-target (19.5%) were identified. Goals from corners were more likely from dynamic attacks or with 1–4 defenders for short corners. Shots on-target were more likely from corners delivered into GA3&CA3 and the outer zones, ≥6 attackers were inside the delivery area or involved ≥3 intervening attackers. Match status was significantly associated with number of defenders, attackers for short corners, defenders for short corners and type of marking. Team quality was significantly associated with type of delivery, kicking foot, number of attackers, attackers for short corners, defenders for short corners, defenders on posts, number of intervening attackers and offensive organisation. Team quality was not significantly associated with corner outcomes, perhaps a consequence of higher-quality teams not always favouring corner characteristics which are associated with increased success (goals or shots on-target). These results can assist coaches to understand corner characteristics to expect when winning, drawing, or losing, or against different levels of opposition within women’s international football.

When a Canadian is not a Canadian: marginalization of IMGs in the CaRMS match.

This paper explores the marginalization experienced by International Medical Graduates (IMGs) in the Canadian Residency Matching Service (CaRMS) Match. This marginalization occurs despite all IMGs being Canadian citizens or permanent residents, and having objectively demonstrated competence equivalent to that expected of a graduate of a Canadian medical School through examinations such as the MCCQE1 and the National Assessment Collaboration OSCE. This paper explores how the current CaRMS Match works, evidence of marginalization, and ethnicity and human rights implications of the current CaRMS system. A brief history of post graduate medical education and the residency selection process is provided along with a brief legal analysis of authority for making CaRMS eligibility decisions. Current CaRMS practices are situated in the context of Provincial fairness legislation, and rationalizations and rationales for the current CaRMS system are explored. The paper examines objective indicators of IMG competence, as well as relevant legislation regarding international credential recognition and labour mobility. The issues are placed in the context of current immigration and education policies and best practices. An international perspective is provided through comparison with the United States National Residency Matching Program. Suggestions are offered for changes to the current CaRMS system to bring the process more in line with legislation and current Canadian value systems, such that “A Canadian is a Canadian.”

Psychological pressure and compounded errors during elite-level tennis

ObjectivesIn the context of Grand Slam tennis, we sought to examine how situational pressure and prior errors can disrupt subsequent performance in elite performers. MethodsA retrospective analysis of more than 650,000 points across 12 Grand Slam tennis tournaments from 2016 to 2019 was conducted to identify pressurised in-game moments and unforced errors. A scoring system was used to index situational pressure based on the current match situation (e.g., break points, stage of the match) on a point-by-point basis. The occurrence of performance errors was identified based on double faults and unforced errors, as instances of controllable mistakes. ResultsA mixed effects logistic regression model revealed that an increase in the pressure index (a 1–5 score) significantly increased the probability of a performance error (ps < .001), as did an error on the preceding point (OR = 1.2, 95%CI [1.17, 1.23], p < .001). A multiplicative effect of pressure and prior errors also emerged, as the negative impact of prior errors on performance was greater when situational pressure was already high, in line with the predictions of Attentional Control Theory: Sport (ACTS). Analyses of the distribution of winners and unforced errors across individual players revealed that winning players were as susceptible to pressure and prior errors as losing players. ConclusionsThese findings extend our understanding of how ongoing feedback from prior mistakes may further exacerbate the effects of pressure on performance.

Photon redistribution of two-terminal perovskite/Si tandem solar cells induced by the optical coupling layer for higher power conversion efficiency

The tandem structure is promising to break the Shockley–Queisser limit of single-junction solar cells. Optical management is essential in two-terminal (2T) tandem devices to equalize the current of each sub-cell and enhance the performance. In this work, the photon redistribution effect caused by the optical coupling layer (OCL) and its impact on 2T perovskite/Si tandem solar cells are systematically investigated. We modulate the overall optical field distribution to balance the current of the two sub-cells by structural modulation. The introduction of an OCL affects the photon distribution in the 2T tandem device, which disturbs the original current match and complicates the optical management. In addition to the antireflection function, the photon redistribution effect due to the coupling effects exists for each type of OCL. Various materials (LiF, MgF2, Al2O3 and ZnO) are employed as OCLs and compared. It is shown that they influence the device performance to different degrees. Compared to LiF and MgF2, the influence of the 2T tandem device on short-circuit current density is more significant when Al2O3 and ZnO act as OCLs. By investigating the optical mechanism and then improving the optical management, an optimized device performance can be achieved. We believe that it is necessary to consider the coupling effect in the structural design of 2T tandem solar cells.

Bidirectional planar-displacement waveguide tracker for high-concentration photovoltaics.

A bidirectional planar-displacement waveguide tracker was devised to replace the traditional two-axis tracking system for high-concentration photovoltaics, with improved module thickness, optical field uniformity, and current matching. The concentrating magnification reaches 725 times, and the sun tracking angle is more than 170°, which is equivalent to 11.3 tracking hours per day. The module thickness is only 6.16 cm. This design enabled us to place the module flat on the ground, in which swing was not required. This will greatly improve the mechanical strength and the lifetime of the module and solve the development dilemma faced by III-V multijunction solar cells.

1 eV GaAsSbN–based solar cells for efficient multi-junction design: Enhanced solar cell performance upon annealing

In this work, we demonstrate the beneficial effect of post-growth rapid thermal annealing (RTA) on the performance of ~1 eV GaAsSbN-based solar cells. Different configurations of the dilute nitride material are studied: a bulk quaternary GaAsSbN layer and type-II GaAsSb/GaAsN superlattices (SL) with different period thickness. The RTA treatment leads in both types of structures to an enhanced external quantum efficiency (EQE) and reduced values of the dark saturation current and series resistance. The origin of these improvements is attributed to reduced densities of N and Sb-rich clusters and point defects. Remarkably, all solar cell parameters are substantially improved, this being particularly significant for the short circuit current density (JSC) and power conversion efficiency (PCE), the latter with a relative enhancement as high as 500%. The large increment of JSC is an important step towards current–matching in multi–junction solar cells containing GaAsSbN structures.

An Exploration of All‐Inorganic Perovskite/Gallium Arsenide Tandem Solar Cells

All‐inorganic perovskite/gallium arsenide (GaAs) tandem solar cells are of great interest for potential space applications. Herein, planar all‐inorganic four‐terminal (4‐T) and two‐terminal (2‐T) perovskite/GaAs tandem solar cells are simulated and optimized, respectively. To achieve higher absorption in the 4‐T configuration, the reflection and parasitic absorption have to be reduced through optimizing the thickness of the perovskite and GaAs base, reducing the thickness of SnO2 and the organic hole transport layer (HTL), and introducing an antireflection coating, respectively. To balance the short‐circuit current and open‐circuit voltage of the GaAs bottom cell, the doping concentration on GaAs is optimized to 1018 cm−3 that has resulted in a high power conversion efficiency (PCE) of 30.97%. Based on the results of 4‐T configuration, all‐inorganic perovskites with different halide compositions are used for current matching to achieve a high‐efficiency 2‐T configuration. After studying the effects of defect density and optimizing the doping concentration of the GaAs base, an extremely high PCE of 30.67% is achieved based on 2‐T CsPbIBr2/GaAs tandem solar cells. Furthermore, the current mismatching under the AM0 spectrum is eliminated for potential high altitude/space application, and the device offers a very competitive PCE of 27.23% compared with that of traditional GaAs double‐junction tandem solar cells.

27.9% Efficient Monolithic Perovskite/Silicon Tandem Solar Cells on Industry Compatible Bottom Cells

Monolithic perovskite/silicon tandem solar cells recently surpass the efficiency of silicon single‐junction solar cells. Most tandem cells utilize &gt;250 μm thick, planarized float‐zone (FZ) silicon, which is not compatible with commercial production using &lt;200 μm thick Czochralski (CZ) silicon. The perovskite/silicon tandem cells based on industrially relevant 100 μm thick CZ‐silicon without mechanical planarization are demonstrated. The best power conversion efficiency (PCE) of 27.9% is only marginally below the 28.2% reference value obtained on the commonly used front‐side polished FZ‐Si, which are about three times thicker. With both wafer types showing the same median PCE of 27.8%, the thin CZ‐Si‐based devices are preferred for economic reasons. To investigate perspectives for improved current matching and, therefore, further efficiency improvement, optical simulations with planar and textured silicon have been conducted: the perovskite's bandgap needs to be increased by ≈0.02 eV when reducing the silicon thickness from 280 to 100 μm. The need for bandgap enlargement has a strong impact on future tandem developments ensuring photostable compositions with lossless interfaces at bandgaps around or above 1.7 eV.

Simulation study of an optimized current matching for In0.39Ga0.61N/In0.57Ga0.43N/In0.74Ga0.26N triple-junction solar cells

Simulation study of an optimized current matching for In0.39Ga0.61N/In0.57Ga0.43N/In0.74Ga0.26N triple-junction solar cells

Wide spectral coverage (0.7–2.2 eV) lattice‐matched multijunction solar cells based on AlGaInP, AlGaAs and GaInNAsSb materials

AbstractWe report on the progress in developing lattice‐matched GaAs‐based solar cells with focus on developing AlGaInP, AlGaAs, and GaInNAsSb materials, aiming at achieving a wide spectral coverage, that is, 0.7–2.2 eV. To this end, we first benchmark the performance of an upright four‐junction GaInP/GaAs/GaInNAsSb/GaInNAsSb solar cells grown by molecular beam epitaxy on p‐GaAs substrates with bandgaps of 1.88, 1.42, 1.17, and 0.93 eV, respectively. The four‐junction cell exhibited an efficiency of ~39% at 560‐sun illumination while showing good electrical performance even up to 1000 suns. As a first step to further improve the efficiency toward 50% level, we demonstrate AlGaInP (&gt;2 eV) and GaInNAsSb (&lt;0.8 eV) subcells. We prove that AlGaInP cells with 0.1 Al composition would exhibit current‐matching condition when being incorporated in a five‐junction architecture together with two GaInNAsSb bottom and AlGaAs top junctions. Furthermore, current matching required for a six‐junction tandem architecture is achieved for an Al composition of 0.26. Overall, the results open a practical path toward fabrication of lattice‐matched solar cells with more than four junctions.