Microstructure-chemomechanics relations of polycrystalline cathodes in solid-state batteries
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25 ENERGY STORAGE↗
SEARCH · Engineering Papers
Results for “polycrystalline”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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A generalizable machine learning-assisted fast Fourier transform algorithm to simulate the large strain phenomena in polycrystalline materials
Machine learning methods have shown initial promise in constitutive modeling for single crystals or homogenized polycrystals, delivering notable computational efficiency. However, existing machine learning-based constitutive models often lack generalizability, limiting their application across diverse boundary value problems. This study introduces a thermodynamics-informed artificial neural network model to accelerate rate-tangent crystal plasticity fast Fourier transform simulations for cross-scale deformation behaviors of polycrystals under complex loading. Our model integrates microstructural variability and local interactions effectively. To address local effects in each grain, we employ K-means clustering to group Gauss points within the microstructure into clusters assumed to be in similar mechanical states. This approach, based on self-clustering analysis, extends model scope from macroscopic stress response to the granular level, capturing mechanical responses and orientation evolution across grains. This reduces the number of nonlinear problems to solve, with cluster responses propagated throughout each group. The thermodynamics-based artificial neural network-extracted features are further processed using local material state clusters to account for history-dependent deformation and evolving microstructures. Additionally, representative volume element simulations with rate-tangent crystal plasticity fast Fourier transform provide reliable datasets for model training. The proposed model demonstrates high efficiency, accuracy, self-consistency, and enhanced generalizability in predicting strain–stress responses and orientation evolution at both individual grain and aggregate scales under complex loading conditions, such as biaxial tension and arbitrary loading scenarios.
36 MATERIALS SCIENCE↗
Low-temperature and effective ex situ group V doping for efficient polycrystalline CdSeTe solar cells
CdTe solar cell technology is one of the lowest-cost methods of generating electricity in the solar industry, benefiting from fast CdTe absorber deposition, CdCl 2 treatment and Cu doping. However, Cu doping has low photovoltage and issues with instability. Doping group V elements into CdTe is therefore a promising route to address these challenges. Although high-temperature in situ group V doped CdSeTe devices have demonstrated efficiencies exceeding 20%, they face obstacles including post-deposition doping activation processes, short carrier lifetimes and low activation ratios. Here, we demonstrate low-temperature and effective ex situ group V doping for CdSeTe solar cells using group V chlorides. For AsCl 3 doped CdSeTe solar cells, the dopant activation ratio can be 5.88%, hole densities reach >2 × 10 15 cm -3 and carrier lifetime is longer than 20 ns. Thus, ex situ As doped CdSeTe solar cells show open-circuit voltages ~863 mV, compared to the highest open-circuit voltage of 852 mV for Cu doped CdSeTe solar cells.
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Chapter 1: Introduction - Motivation of Polycrystalline Thin-Film Solar Cells
Thin-film solar cell development may be conceptualized as improving processes to lower costs and improve performance, with characterization as a guide along the way. Yet, pushing the boundaries of characterization is as much at the core of thin-film solar cell development as material synthesis. As PV continues to mature, there is an endless drive to improve performance to compete. Hence, PV technology is striving for increasing levels of perfection, requiring a corresponding sophistication in characterization and understanding. Consequently, the topic of this book -advanced characterization-is timely and critical to develop the potential of thin-film solar technology.
material synthesis↗
Chapter 8: Time-Resolved Photoluminescence Characterization of Polycrystalline Thin-Film Solar Cells
This chapter describes some photoluminescence (PL) approaches to characterize thin film solar cells with emphasis on time-resolved methods. Spectral PL analysis is complementary and was recently reviewed. Since TRPL is not very commonly used in PV characterization, we consider interface and bulk recombination in the test structures and in devices, briefly describe charge-carrier transport and recombination microscopy, and finally, summarize and compare some CdTe, CdSeTe, CIGS, kesterite, and perovskite EO characteristics.
bulk recombination↗
Large-scale atomistic studies of sliding friction in polycrystalline aluminum interfaces
In this work, we discuss large-scale non-equilibrium molecular dynamics (NEMD) simulations of ductile metal sliding comprising up to 1.8 × 10 9 atoms over time scales of 100 ns. The results of these simulations have identified a variety of physical mechanisms that are important in determining the steady-state frictional force for a wide range of velocities at compressed metal–metal interfaces. These include grain growth and refinement, the evolution of large plastic strains and strain rates, material mixing, and melting. These phenomena can be included in a strain, strain rate, and grain size model that gives good agreement with the NEMD simulations and can be applied to macroscopic continua.
74 ATOMIC AND MOLECULAR PHYSICS↗
Spatially and Spectrally Resolved Defects in Polycrystalline CdTe Thin Films Revealed by Quantitative Cathodoluminescence
Increasing the grain size is a potential strategy to reduce grain-boundary recombination and improve performance of thin-film solar cells. Here, CdTe thin films with a range of grain sized were produced by varying the CdC1 2 post-deposition treatment temperature. We use high-resolution cathodoluminescence (CL) microscopy to study recombination and shallow defect levels in detail. Intensities from room temperature CL maps were compared across samples. We find that the CL intensity initially increases with grain size, as expected, but then plateaus as the grain size is increased further. The plateau is correlated with a decrease in the characteristic length-related to the carrier diffusion length-determined from CL intensity profiles near grain boundaries. In addition, low-temperature CL measurements demonstrate the evolution of the defect levels with CdC1 2 temperature.
cadmium telluride thin films↗
Synthesis and characterization of electron beam irradiation-induced damage in polycrystalline metal thin films
High-energy physics research, industrial sterilizing, and material processing depend extensively on electron beam accelerators. Exit windows are crucial components of such electron accelerator systems, maintaining vacuum integrity inside the machine while providing mechanical strength, thermal stability, and radiation resistance at the beam-target interface. In this study, thin metallic films of Ni, Ti, Cr, and V were explored for use in electron beam exit windows, and their properties were compared with the properties of their bulk counterparts. Simulation results of metal foils predicted Ti to exhibit less beam power dissipation compared to Ni. However, Ni possesses superior mechanical and structural properties compared to Ti. The performance of these films under electron beam irradiation was examined by depositing thin layers of these films on silicon and metallic substrates using magnetron sputtering and exposing them to e-beam irradiation in a controlled setup. The deposited films were subjected to a dose of approximately 66 kGy at a beam energy of 10 MeV and characterized prior to and postexposure to the beam using field emission scanning electron microscopy, atomic force microscopy, x-ray diffraction (XRD), and nanoindentation. Particular emphasis was given to characteristics like the grain structure, surface morphology, dislocation density, and hardness. XRD patterns revealed irradiation-induced changes in peak intensities, while the crystallinity remained largely unchanged. Nanoindentation results showed that the pristine and irradiated Ti and Ni films were twice as hard when compared to bulk Ti and Ni samples, regardless of the substrate type used (Si or bulk Ti, or Ni). These results emphasize the superior mechanical properties of thin metal films compared to their bulk counterparts. In conclusion, this study advances the optimization of thin film materials for robust and efficient e-beam applications, ensuring improved durability and operational reliability.
AFM↗
Magnetostriction of Polycrystalline Tb-Dy at Cryogenic Temperatures
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cost↗
Damp Heat Degradation of Polycrystalline Silicon Passivated Contacts
After 1000 hours of damp heat exposure at 85% humidity and 85 C, LPCVD n-poly and p-poly are stable for both metallized and non-metallized regions whereas for PECVD, only n-poly is stable; PECVD p-poly suffers significant degradation and defects became more pronounced with exposure time; and PECVD p-poly degrades more than LPCVD p-poly with or without additional dielectric layers (i.e., SiNx + Al2O3 stack).
damp heat degradation↗
Engineering Polycrystalline Perovskite for Low-Cost Pixelated X-Ray Imager
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Confinement‐Driven Inverse Domain Scaling in Polycrystalline ErMnO 3
Abstract The research on topological phenomena in ferroelectric materials has revolutionized the way people understand polar order. Intriguing examples are polar skyrmions, vortex/anti‐vortex structures, and ferroelectric incommensurabilties, which promote emergent physical properties ranging from electric‐field‐controllable chirality to negative capacitance effects. Here, the impact of topologically protected vortices on the domain formation in improper ferroelectric ErMnO 3 polycrystals is studied, demonstrating inverted domain scaling behavior compared to classical ferroelectrics. It is observed that as the grain size increases, smaller domains are formed. Phase field simulations reveal that elastic strain fields drive the annihilation of vortex/anti‐vortex pairs within the grains and individual vortices at the grain boundaries. The inversion of the domain scaling behavior has far‐reaching implications, providing fundamentally new opportunities for topology‐based domain engineering and the tuning of the electromechanical and dielectric performance of ferroelectrics in general.
36 MATERIALS SCIENCE↗
Investigation of Sub‐Bandgap Emission and Unexpected n‐Type Behavior in Undoped Polycrystalline CdSe x Te 1‐x
Abstract Se alloying has enabled significantly higher carrier lifetimes and photocurrents in CdTe solar cells, but these benefits can be highly dependent on CdSe x Te 1‐x processing. This work evaluates the optoelectronic, chemical, and electronic properties of thick (3 µm) undoped CdSe x Te 1‐x of uniform composition and varied processing conditions (CdSe x Te 1‐x evaporation rate, CdCl 2 anneal, Se content) chosen to reflect various standard device processing conditions. Sub‐bandgap defect emission is observed, which increased as Se content increased and with “GrV‐optimized CdCl 2 ” (i.e., CdCl 2 anneal conditions used for group‐V‐doped devices). Low carrier lifetime is found for GrV‐optimized CdCl 2 , slow CdSe x Te 1‐x deposition, and low‐Se films. Interestingly, all films (including CdTe control) exhibited n‐type behavior, where electron density increased with Se up to an estimated ≈10 17 cm −3 . This behavior appears to originate during the CdCl 2 anneal, possibly from Se diffusion leading to anion vacancy (e.g., V Se , V Te ) and Cl Te generation.
14 SOLAR ENERGY↗
First Principles Study of Aluminum Doped Polycrystalline Silicon as a Potential Anode Candidate in Li‐ion Batteries
Addressing sustainable energy storage remains crucial for transitioning to renewable sources. While Li‐ion batteries have made significant contributions, enhancing their capacity through alternative materials remains a key challenge. Micro‐sized silicon is a promising anode material due to its tenfold higher theoretical capacity compared to conventional graphite. However, its substantial volumetric expansion during cycling impedes practical application due to mechanical failure and rapid capacity fading. A novel approach is proposed to mitigate this issue by incorporating trace amounts of aluminum into the micro‐sized silicon electrode using ball milling. Density functional theory (DFT) is employed to establish a theoretical framework elucidating how grain boundary sliding, a key mechanism involved in preventing mechanical failure is facilitated by the presence of trace aluminum at grain boundaries. This, in turn, reduces stress accumulation within the material, reducing the likelihood of failure. To validate the theoretical predictions, capacity retention experiments are conducted on undoped and Al‐doped micro‐sized silicon samples. In conclusion, the results demonstrate significantly reduced capacity fading in the doped sample, corroborating the theoretical framework and showcasing the potential of aluminum doping for improved Li‐ion battery performance.
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As‐Doped Polycrystalline CdSeTe: Localized Defects, Carrier Mobility and Lifetimes, and Impact on High‐Efficiency Solar Cells
Abstract The efficiency potential for single‐junction photovoltaics (PV) is described by the detailed balance model, which requires the elimination of nonradiative recombination and perfect minority carrier collection. Improvements in GaAs, Si, and perovskite PV follow this model. It might be more complex for CdTe, a leading thin‐film PV technology. While lifetime, passivation, and doping goals for 25% efficient CdTe solar cells are largely reached, voltage is ≈20% below the detailed balance limit. Why is that? In Se‐alloyed CdSe x Te 1‐x (Se is required for >20% efficiency) additional losses can occur due to electrostatic and bandgap fluctuations and due to electronic trap states. To understand mechanisms limiting CdSeTe solar cell performance and to suggest improvements, carrier dynamics, and transport in CdSe x Te 1‐x with variation in Se composition and as doping is analyzed. It is shown that trapping, likely due to anion‐site defects and their complexes, is correlated with low charge carrier mobility of 0.1–0.6 cm 2 (Vs) −1 . Even with 1000 ns charge carrier lifetimes, carrier diffusion length is less than the absorber thickness, reducing efficiency to ≈23%. Device simulations are used to analyze the performance of CdSe x Te 1‐x solar cells; thermodynamic models are not sufficient for absorbers with electronic disorder and trapping.
14 SOLAR ENERGY↗
Microwave Annealing for Fast and Effective Hydrogen Activation in Polycrystalline Silicon Passivating Contacts
Hydrogenation is a crucial step in the fabrication of high-efficiency silicon solar cells. In this study, the effectiveness of hydrogen activation is demonstrated via microwave annealing of hydrogen-rich dielectrics coated on poly-Si passivating contacts. This method is compared with conventional hydrogenation techniques, such as annealing in N2 in the presence of a hydrogen-rich source (such as hydrogenated aluminum oxide (AlOx:H), hydrogenated silicon nitride (SiNy:H), or a AlOx:H/SiNy:H stack). Key improvements observed include a reduction in J0 from 30 to <5 fA cm-2, an increase in iVoc from 690 to >730 mV, and an enhancement in effective lifetime (teff) from 0.6 to ~3.5 milliseconds on phosphorus-doped poly-Si/SiO2 passivating contact samples. With a very short annealing time of ~1-2 min, the samples passivated by AlOx:H, SiNy:H, or the stack show similar performance to samples subjected to 30 min of nitrogen annealing. Photoluminescence (PL) spectra corroborate the findings regarding the hydrogenation of the poly-Si layer and the c-Si substrate, with an increase in PL intensity after microwave annealing. Ultimately, this work suggests that microwave annealing could be a promising addition, offering flexibility to traditional firing hydrogenation processes.
hydrogenation↗
Modeling Microstructural Effects on Heterogeneous Temperature Fields within Polycrystalline Explosives
The paper addresses the role of crystal anisotropy on the evolution of heterogeneous temperature fields in plastic-bonded explosives (PBXs) under conditions of weak shock. The modeling approach is based on simplified idealizations of PBX microstructure including RDX grains and estane binder regions subjected to velocity boundary conditions representative of impact conditions in situ. The constitutive description of the microstructure constituents includes a dislocation-based, anisotropic, single crystal plasticity model for the explosive grains and a linear viscoelastic model to represent the estane binder. Large suites of simulations were used to systematically study the correlation in heating of the grains with local wave dynamics, crystal orientation, and the microstructural neighborhood. These correlations were identified through the selection of characteristics of crystal anisotropy including oriented wave speeds and Taylor factor. A key observation is that the wave dispersion within a certain distance from the impact interface plays a dominant role in the temperature field. Beyond this distance, individual crystal orientations play a more dominant role, but cannot entirely account for the observed heterogeneity without consideration of the local microstructure neighborhood.
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Understanding the Role of CdTe in Polycrystalline CdSe x Te 1– x /CdTe-Graded Bilayer Photovoltaic Devices
Grading of bandgap by alloying CdTe with selenium to form a CdSe x Te 1–x /CdTe-graded bilayer device has led to a device efficiency over 19%. A CdSe x Te 1–x absorber would increase the short-circuit current due to its lower bandgap but at the expense of open-circuit voltage. It has been demonstrated that adding a CdTe layer at the back of such a CdSe x Te 1–x film reduces the voltage deficit caused by the lower bandgap of absorber from selenium alloying while maintaining the higher short-circuit current. This leads to a photovoltaic device that draws advantage from both materials with an efficiency greater than either of them. In this report there is a detailed account using device data, ultraviolet photoelectron spectroscopy, electron microscopy, and first-principles density functional theory modeling is provided, which shows that CdTe acts as an electron reflector for CdSe x Te 1–x .
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗