Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Contacts”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Self-Aligned, Selective Area Poly-Si/SiO2 Passivated Contacts for Enhanced Photocurrent in Front/Back Solar Cells: Preprint

Poly-Si/SiO2 passivated contact front/back solar cells suffer low Jsc due to parasitic absorption in the front poly-Si layer. We demonstrate a self-aligned, selective area front contact dry-etch technique that retains the as-deposited poly-Si beneath the metal grid lines but thins it elsewhere. Jsc improves by 0.7 mA/cm2 over our standard 40 nm thick poly-Si. Greater improvements are expected with thicker poly-Si needed for fired metal contacts. Surface passivation is slightly diminished with poly-Si thinning but can be partially restored with re-hydrogenation.

14 SOLAR ENERGY↗
DOE OSTI2020

Quantitative Understanding and Implementation of Screen Printed p+ Poly-Si/Oxide Passivated Contact to Enhance the Efficiency of p-PERC Cells

This paper reports on the modeling, optimization and implementation of p-TOPCon (tunnel oxide passivated contacts) on the rear side of a PERC to enhance its efficiency. Local Al-BSF of a traditional PERC was replaced by p+ polySi/oxide passivated contact composed of ~15Å thick chemically grown tunnel oxide, capped with 120-250nm thick p+ poly-Si layer grown by LPCVD. Process optimization resulted in full area unmetallized saturated current density (Jo) of ~ 5fA/cm2 for planar surface, nearly independent of poly-Si thickness in the range. Metallized J0 showed an increase with decreased poly-Si thickness and was found to be 9.6 and ~25fA/cm2 for 250nm and 120 nm polySi, respectively, with 4.6% direct metal-Si contact fraction, suitable for bifacial cells. A 21.4% efficient baseline PERC cell with local BSF was fabricated and analyzed to extract the rear side saturation current density (J0b’) of 66fA/cm2. Model calculations showed that by replacing this local BSF with 250nm TopCon developed in the study showed some Voc enhancement of 7mV, consistent with the observed Voc increase of 10mV. Model calculations also reveal that a more advanced LBSF PERC with better bulk lifetime and emitter saturation current density can extends its potential gain up to 0.4% in cell efficiency from the integration of p-TOPCon.

14 SOLAR ENERGY↗
DOE OSTI2023

High-Performance Passivating Contacts for Si PV Based on Engineered, Doped Nanopinholes through Dielectric Layers

We present a novel, industrially relevant method to fabricate high-performance poly-Si passivating contacts for Si PV. Passivating contacts based on SiOx/poly-Si layer stacks have been implemented in record-efficiency homojunction Si solar cells. In this technology, the carrier transport through a surface-passivating SiOx is enabled either by quantum-tunneling or nanopinholes. The doped poly-Si layer provides charge-carrier selectivity. Previously, the ISFH research group demonstrated a record 26.1% efficient Si homojunction cell, where transport pinholes in ~2 nm SiOx were produced by thermal breakdown at > 1000 degrees C, which is hard to control and is surface morphology-dependent. At room temperature, our new process uses electroless plating of Ag nanoparticles, followed by metal-assisted chemical etching. Nanogalvanic corrosion yields < 20 nm-wide nanopinholes in an insulating > 2 nm SiOx layer. The nanopinholes are filled by a heavily doped a-Si:H overlayer. We drive in the dopants into the Si wafer with subsequent high-temperature annealing. Preferential incorporation of dopants at pinhole locations results in nanoscale p+/n or n+/n junctions near the wafer interface. Each heavily-doped nanoscale pinhole junction collects and transports photogenerated carriers to the cell metal contacts. The density of the engineered nanopinholes can be tuned over a wide range which is critical for optimization of device performance. The same nanogalvanic corrosion principles can be applied to produce doped transport pinholes in well-passivating thick dielectric SiOx/SiNy stacks. Importantly, our process does not rely on thermal breakdown of the dielectric layers and can be applied to textured wafers resulting in Si solar cells with > 20% conversion efficiency.

dielectric layer↗
DOE OSTI2020

Low-Dimensional Contact Layers for Enhanced Perovskite Photodiodes

Controlling defects and energy-band alignments are of paramount importance to the development of high-performance perovskite-based photodiodes. Yet, concurrent improvements in interfacial contacts and defect reduction simply by tailoring bottom contacts have not been investigated. An effective strategy is reported that can simultaneously improve energy-band alignments and structural defects by introducing low-dimensional contact (LDC) layers at the bottom interface. It is found that LDC-based perovskites considerably suppress undesirable structural defects induced by microstrains, resulting in reduced nonradiative recombination centers and improved carrier lifetimes. Additionally, the resulting LDC-based interface structures help block minority carrier injection from the electrodes by forming built-in electric fields. As a consequence, LDC-based perovskite photodiodes showed improved light detection capabilities. Finally, the result opens an avenue to yield highly efficient photodiodes.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Thin insulating tunneling contacts for efficient and water-resistant perovskite solar cells

Here, we demonstrated that inserting a tunneling layer between perovskite and electron transport layer could significantly increase device performance by suppressing carrier recombination at the cathode contact. The tunneling layer can also serve as an encapsulation layer to prevent perovskite film from damage caused by water or moisture. This method is simple because it does not need lattice matching between the buffer layer and perovskite. The low temperature solution process makes it compatible with many types of perovskite materials, and may be applied for anode contact as well. The freedom to choose any insulating layer for contact enables more device designs and manufacturing.

25 ENERGY STORAGE↗
DOE OSTI2021

Modeling of transport in carrier-selective contacts in silicon heterojunction solar cells

High-performance silicon heterojunction (SHJ) solar cells use carrier-selective contact structures based on hydrogentated amorphous Si (a-Si:H) to maximize collection of photogenerated carriers. The high open circuit voltages observed experimentally in SHJ cells require that the carrier-selective contacts provide selectivity and passivation. However, a microscopic understanding of the dynamics of carrier transport through the a-Si layer is currently lacking. In this paper, we explicitly simulate the transport of holes across the a-Si:H(i) layer using a novel kinetic Monte Carlo approach. The hole-selective contact structure investigated in this paper uses p-type doped a-Si:H(p) and intrinsic a-Si:H(i) on an n-type crystalline silicon wafer, where the selectivity is provided by the a-Si:H(p) and the passivation is provided by the a-Si:H(i). However, in addition to the passivation provided by the a-Si:H(i), this layer also creates a potential barrier to the collection of photogenerated holes. There have been experimental studies in the literature that have suggested that multi-phonon processes are the main transport mechanism that assists in the transport of holes across the intrinsic a-Si:H barrier. Simulations presented here show that multi-phonon injection of holes into the a-Si:H(i) layer is the rate limiting step for transport across the a-Si:H(i) layer. Our results indicate that multi-phonon transport is strongly dependent on the electric field at the a-Si:H(i)/c-Si heterointerface as well. Transport simulations presented in this paper are consistent with experimental findings that multi-phonon processes limit transport across the a-Si:H(i) layer and are responsible for photocurrent suppression at the a-Si:H(i)/c-Si heterointerface when these processes are slower than the associated incident hole flux due to photo-excitation.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

In Situ Transmission Electron Microscopy Study of Molybdenum Oxide Contacts for Silicon Solar Cells

Here, a molybdenum oxide (MoO x ) and aluminum (Al) contact structure for crystalline silicon (c-Si) solar cells is investigated using a combination of transmission line measurements (TLM) and in-situ transmission electron microscopy (TEM). Cross-sectional high-resolution TEM (HRTEM) micrographs reveal a ≈2 nm silicon oxide (SiO x ) interlayer at c-Si/MoO x interface in the as-deposited state, indicating that formation of SiO x occurs during deposition of MoO x . Moreover, oxygen diffusion takes place from MoO x toward Al resulting in the formation of a ≈2–3 nm aluminum oxide (AlO x ) interlayer at the MoO x /Al interface. Overall, it is observed that MoO x /Al contact is relatively stable upon annealing up to 200 °C and still retains ohmic transport with sufficiently low contact resistivity.

14 SOLAR ENERGY↗
DOE OSTI2020

Molybdenum Contacts to MoS 2 Field‐Effect Transistors: Schottky Barrier Extraction, Electrical Transport, and Low‐Frequency Noise

MoS 2 has great interest for nanoscale electronic devices, including transistors and sensors. Defect‐free structure, clean interface with the gate dielectric, and metals with suitable metal–semiconductor junctions are key for reliable devices. Molybdenum is shown as an excellent electrode for MoS 2 field‐effect transistors (FETs), but the correlation among device current, field‐effect mobility, and the low‐frequency noise (LFN) with number of atomic layers is not studied. Furthermore, the impact of Mo/MoS 2 Schottky barrier on electronic injection and scattering in the device needs to be understood. Herein, by studying the FETs with channels of different numbers of atomic‐layer thicknesses, it is shown that a molybdenum metal contact to MoS 2 provides reliable current injection with low Schottky barrier height, low contact resistance, low electron–phonon scattering, and negligible impurity scattering. The mobility and LFN are optimal at a channel thickness of ≈12 atomic layers, which is consistent with the “mobility maximum window” in MoS 2 transistors with prior studies using other contact metals.

Kwon, Jiseok↗
DOE OSTI2023

Stable Cycling with Intimate Contacts Enabled by Crystallinity–Controlled PTFE–Based Solvent–Free Cathodes in All–Solid–State Batteries

All-solid-state batteries (ASSBs) employing Li-metal anodes and inorganic solid electrolytes are attracting great attention due to high safety and energy density for next-generation energy storage devices. However, the volume change of cathode active materials can cause contact loss, resulting in charge carrier isolation, heterogeneous current distribution, and poor electrochemical properties in ASSBs. Here, a simple, yet effective, solvent-free electrode engineering approach with polytetrafluoroethylene (PTFE) as a binder for ASSBs is reported, enabling intimate contact and stable interfaces with the cathode. It is substantiated that the crystallinity of PTFE can be controlled depending on the heat history, and highly crystalline PTFE displays robust mechanical properties. High-nickel LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathode prepared with crystalline PTFE show improved cycle and rate performances in ASSBs. In addition, it is revealed that the intimate contact between cathode particles with a stable cathode electrolyte layer is maintained during cycling by postmortem studies. Furthermore, this simple engineering method can be applied to prepare cathodes with a variety of active materials and solid electrolytes in ASSBs.

25 ENERGY STORAGE↗
DOE OSTI2024

Characterizing 4-string contact interaction using machine learning

Abstract The geometry of 4-string contact interaction of closed string field theory is characterized using machine learning. We obtain Strebel quadratic differentials on 4-punctured spheres as a neural network by performing unsupervised learning with a custom-built loss function. This allows us to solve for local coordinates and compute their associated mapping radii numerically. We also train a neural network distinguishing vertex from Feynman region. As a check, 4-tachyon contact term in the tachyon potential is computed and a good agreement with the results in the literature is observed. We argue that our algorithm is manifestly independent of number of punctures and scaling it to characterize the geometry ofn-string contact interaction is feasible.

Physics↗
DOE OSTI2016

History-Dependent Problems with Applications to Contact Models for Elastic Beams

We prove an existence and uniqueness result for a class of subdifferential inclusions which involve a history-dependent operator. Then we specialize this result in the study of a class of history-dependent hemivariational inequalities. Problems of such kind arise in a large number of mathematical models which describe quasistatic processes of contact. To provide an example we consider an elastic beam in contact with a reactive obstacle. The contact is modeled with a new and nonstandard condition which involves both the subdifferential of a nonconvex and nonsmooth function and a Volterra-type integral term. We derive a variational formulation of the problem which is in the form of a history-dependent hemivariational inequality for the displacement field. Then, we use our abstract result to prove its unique weak solvability. Finally, we consider a numerical approximation of the model, solve effectively the approximate problems and provide numerical simulations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

The Relevance of Pion-Exchange Contributions Versus Contact Terms in the Chiral Effective Field Theory Description of Nucleon–Nucleon Scattering

The standard way to demonstrate the relevance of chiral symmetry for the NN interaction is to consider higher partial waves of NN scattering which are controlled entirely by chiral pion-exchanges (since contacts vanish). However, in applications of NN-potentials to nuclear structure and reactions, the lower partial waves are the important ones, making the largest contributions. Lower partial waves are sensitive to the short-range potential, and so, when the short-range contacts were to dominate over the chiral pion contributions in lower partial waves, then the predictions from chiral potentials would have little to do with chiral symmetry. To address this issue, we investigate systematically the role of the (chiral) one- and two-pion exchanges, on the one hand, and the effect of the contacts, on the other hand, in the lower partial waves of NN scattering. We are able to clearly identify the signature of chiral symmetry in lower partial waves. Furthermore, our study has also a pedagogical spinoff as it demonstrates in detail how the reproduction of the lower partial-wave phase shifts comes about from the various ingredients of the theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Contact Problem of Wear of the Elastic Half Plane with Winkler’s Coating Caused by Punches of Canonical Shapes

The problem of contact interaction of punches of canonical shapes (cylindrical, elliptic, and hyperbolic) with elastic half planes covered with protective coatings is solved with regard for the wear of the material. We propose a method for the solution of the singular integrodifferential equation of the problem. The numerical analysis of contact pressure is performed for different times, and some specific features of wear of the material by the punches of different shapes are discovered. The time for which the coating is totally worn out at a given point of the contact zone is determined.

42 ENGINEERING↗
DOE OSTI2018

Smooth Contact of a Semiinfinite Punch with Rounded Edge and an Elastic Strip

We consider a problem of contact of an elastic strip with a semiinfinite punch with rounded edge indented into one face of the strip, while the other face of the strip is fixed. Friction forces in the contact zone are neglected. By the Wiener–Hopf method, we obtain the exact analytic solution of the problem. The distributions of contact stresses, the stresses inside the strip and along its fixed face, and the normal displacements of points of a part of the load-free face of the strip are determined. We construct the isochores and determine the position of the point at which the maximum values of the principal shear stresses are attained.

42 ENGINEERING↗
DOE OSTI2019

Influence of Effective Physical Contact Area on Microstructure and Mechanical Properties of Diffusion-Bonded TC4/1060Al Joints

In the present study, dissimilar TC4 alloy and 1060Al alloy were successfully diffusion-bonded at a very low temperature about 410 °C by improving the effective physical contact area. A sound joint with a crack-free interface and a high shear strength (128 MPa) is obtained with a combination of TC4 surface roughness of 109.90 μm (S{sub a}) and 1060Al surface roughness of 101.43 μm (S{sub a}), and customized parallel surface scratches. Under this condition, the two parent metals share the largest contact area during the physical contact stage of diffusion bonding process, which is consistent with the theoretical calculation. The results show that no Ti-Al binary intermetallic compounds are observed at the interface of the joints. The maximum shear strength of the joint reaches 128 MPa with optimized bonding parameters (410 °C for 120 min with a pressure of 20 MPa), which is higher than the shear strength of 1060Al (80 MPa) base metal. The fractography analysis indicates the joints failed with a ductile fracture at the 1060Al side.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Spontaneous imbibition of water and determination of effective contact angles in the Eagle Ford Shale Formation using neutron imaging

Understanding of fundamental processes and prediction of optimal parameters during the horizontal drilling and hydraulic fracturing process results in economically effective improvement of oil and natural gas extraction. Although, the modern analytical and computational models can capture fracture growth, there is a lack of experimental data on spontaneous imbibition and wettability in oil and gas reservoirs for the validation of further model development. In this work, we used neutron imaging to measure the spontaneous imbibition of water into fractures of Eagle Ford Shale with known geometries and fracture orientations. An analytical solution for a set of nonlinear second-order differential equations was applied to the measured imbibition data to determine effective contact angles. The analytical solution fit the measured imbibition data reasonably well and determined effective contact angles were slightly higher than static contact angles due to effects of in-situ changes in velocity, surface roughness, and heterogeneity of mineral surfaces on the fracture surface. Additionally, small fracture widths may have retarded imbibition and affected model fits, which suggests that average fracture widths are not satisfactory for modeling imbibition in natural systems.

DiStefano, Victoria H. (ORCID:0000000160239716)↗
DOE OSTI2025

Direct root contact among neighboring plants influences activity of soil extracellular enzymes

Composition and diversity of vegetation systems can influence soil microbial activity and extracellular enzyme (EE) dynamics, which are crucial for soil carbon (C) accrual and nutrient cycling. Yet, the impact of plant interactions and competition on EE activities remains a notable knowledge gap. This study examines how direct root contact and neighboring plant identity affect the activity and spatial distribution of four key soil EEs: β-glucosidase (BGlu), chitinase, acid phosphatase (AcidP), and alkaline phosphatase (AlkP). Using three-compartment rhizoboxes with switchgrass (Panicum virgatum L.) grown alongside bush clover (Lespedeza capitata Michx.), and black-eyed Susan (Rudbeckia hirta L.), we assessed enzyme activities using zymography under conditions that either allowed or restricted direct root contact by root barriers. Results show that root proliferation and species interactions significantly influenced EE activity. While BGlu and AcidP activities were strongly correlated with root biomass, AlkP activity was consistently higher in the absence of root barriers, indicating a pronounced microbial response to plant interactions via direct/close root contacts. Additionally, soil phosphorus availability modulated enzyme activity, with higher phosphatase activities in low-P soils. Furthermore, these findings highlight the importance of root-root interactions and plant species composition in shaping soil biochemical processes.

enyzme activity↗
DOE OSTI2022

Evaluation of PbTe and SnTe as Ohmic Contact Layers in CdTe Solar Cell Devices

For solar cells based on CdTe, the choice of a suitable back contact material is limited by CdTe's deep work function. Here, we explored p-type PbTe and SnTe as ohmic contacts to CdTe. These contact layers were grown on single crystal CdTe substrates by molecular beam epitaxy, and the valence band offset between film and substrate was measured using X-ray photoemission spectroscopy. Polycrystalline device structures were also grown by sublimation to assess performance improvements. Doping was achieved in PbTe by thallium incorporation. Only the highest Tl doped PbTe resulted in a desirable band alignment with the CdTe, forming an electron reflector and no hole barrier. Time-resolved photoluminescence measurements also revealed significant photocarrier lifetime improvements for only the highest doped PbTe. Consequentially, devices incorporating the highest doped PbTe layers showed increased power conversion efficiency, primarily from increased fill factor. Doping of the PbTe was measured via Hall effect with variable magnetic field, which was required due to the formation of an n-type parasitic interface layer. To properly interpret the variable field Hall measurements, we derived an expression for the magnetic field-dependent conductivity tensor of an L-valley semiconductor.

anisotropic band valley↗