Stainless Steel Foil Substrates Research Articles

High-performance radial junction solar cells on ZnO coated stainless steel with excellent flexibility and durability

High flexibility and industrial compatibility are the key factors for developing large-scale lightweight, wearable, and portable thin film flexible solar cells. Here, a rather flexible and mechanically durable three-dimensional (3D) radial junction (RJ) solar cell has been directly constructed over discrete standing Si nanowires (SiNWs), upon flexible ZnO-coated stainless steel (SS) foil substrates. The ZnO layer deposited on the SS surface can optimize the density of SiNWs to improve the optoelectronic performance. A power conversion efficiency of 6.01% has been accomplished, with open-circuit voltage and photo-current density of 0.76 V and 12.87 mA/cm2, respectively. Remarkably, the outstanding mechanical stability of these RJ devices has been recorded, which can sustain > 4000 cycles of large bending to a radius of 2.5 mm, with only a 7% efficiency decrease. Note that the one-pump-down fabrication procedure of this 3D nanostructure RJ cells upon flexible ZnO-coated SS substrates is compatible with the industrial-mainstream Roll-to-Roll technology, holding thus a strong promise to establishing a simple and low-cost strategy for high-performance and durable flexible photovoltaics.

Characterization of Cu(In,Ga)(Te,S)2 thin films grown on stainless steel foil substrates

In this study, Cu(In,Ga)(Te,S)2 (CIGTS) thin films with [Ga]/([In] ± [Ga]) atomic ratios in the ranges of 0.22–0.28 and 0.50–0.67 were fabricated using a two-stage technique. During the first stage of the technique, in one set of samples, Cu, In and Ga layers were deposited by electrodeposition on a Mo coated stainless steel (SS) foil substrate forming a SS/Mo/Cu/In/Ga precursor structure. For another set of samples, a Te layer was also deposited by e-beam evaporation on the SS/Mo/Cu/In/Ga structure forming a SS/Mo/Cu/In/Ga/Te precursor structure. During the second stage, SS/Mo/Cu/In/Ga and SS/Mo/Cu/In/Ga/Te stacks were reacted using rapid thermal annealing (RTA) for 5 min at 600 °C with or without presence of S vapors to produce CIGTS series thin films. SS/Mo/Cu/In/Ga stack under S atmosphere yielded CuInGaS2 with a Ga-In gradient across the thickness by RTA process. SS/Mo/Cu/In/Ga/Te stack reacted without S in the reaction atmosphere yielded the CuInGaTe2 compound. When S was present, the same stack with top Te layer yielded only CuInGaS2 compound. When, however, already formed CuInGaTe2 compound layers were heated in S environment at 400 °C, some Te could be retained in the films in the form of elemental Te. Gallium and In grading in various reacted films were evaluated by x-ray diffraction, secondary-ion mass spectrometry and EDS. CIGTS films showed highly (112) preferred oriented chalcopyrite phase and with the increase of Ga content, shifts were observed in the XRD peak positions demonstrating Ga inclusion in the lattice. Gibbs free energy calculations were used to explain the preferred reaction of S with metallic constituents when both S and Te were present for reaction.

Toward lossless photovoltaic efficiency of Laser-shaped flexible Cu(In,Ga)Se2 solar cells on stainless steel substrates

Flexible Cu(In,Ga)Se2 (CIGS) solar cells on metal substrates are susceptible to thermal effects during laser shaping, resulting in their failure. In this study, a two-step scribing–cutting approach for shaping CIGS cells on stainless steel foil substrates was developed. Electrical–thermal dual isolations were performed by laser scribing to guard against damage to the CIGS cells during the laser shaping process. The efficiency loss ratio after an ultraviolet nanosecond laser shaping decreased from an average of 80% for the one-step method to an average of < 10% for the two-step method. The efficiency loss could be further decreased with a larger cell area of > 1 cm2, which is closer to lossless laser shaping. This method was also demonstrated successfully on curved-shaped cells. This work opens up the prospect of using laser shaping in the mass manufacture of flexible CIGS solar cells on metal substrates.

Investigation of Vacuum Arc-Deposited ta-C and ta-C:N Thin Films on Silicon and Stainless-Steel Foil Substrates Using Raman Spectroscopy

In this paper, we investigated the vacuum arc-deposited tetrahedral amorphous carbon (ta-C) and nitrogen-doped ta-C (ta-C:N) thin films grown on silicon and stainless-steel foil substrates by the visible Raman Spectroscopy. We found that carbon films grown on silicon surfaces prefer more sp3 hybridized carbon compared to the stainless-steel foil, which prefer more sp2 hybridized carbon even though the films are grown concurrently under the same conditions. The impact energy of plasma ions modifies the interfacial layer formation, giving a strong dependence of the sp2/sp3 ratio with the substrate bias, behaving differently for different substrates. However, nitrogen doping in amorphous carbon thin films helps to increase sp2 contents uniformly on both the surfaces for a fixed substrate bias. Understanding such interfaces are of interest for many electronic, optoelectronic, and energy storage devices as these interfaces get buried and can influence the properties significantly.

Large‐area, high‐temperature stainless steel foil substrate for manufacturing low‐cost and flexible CMOS polysilicon TFTs

AbstractA large‐area stainless steel foil substrate which is compatible with high‐temperature (&gt;800°C) processing was developed to support a hybrid printed and conventional process technology to fabricate polysilicon thin‐film transistors (TFTs). The purpose was to build a platform that could lead to low‐cost, roll‐to‐roll manufacturing of polysilicon TFTs. To fabricate a self‐aligned top‐gate TFT structure, a screen‐printed dopant process, which requires high‐temperature activation, was developed to substitute capital‐intensive ion implantation. For the pilot line process, a 300‐mm2 and 100‐μm‐thick stainless steel substrate made of an alloy with a low thermal expansion coefficient (CTE) was chosen. Then, the foil finishing process was optimized to achieve flatness and minimize surface roughness. A barrier and dielectric encapsulation were developed to prevent trace metal diffusion from the substrate into the active layers. The polysilicon TFTs were then evaluated with static and dynamic bending tests.

Formulation and characterization of screen printable dopant ink for fabrication of polysilicon TFTs

To move the promise of printed electronics from the laboratory to volume production required adopting a new approach eliminating ink-jet printing and adopting instead a hybrid mature print and conventional process. Novel screen printable N+ and P+ dopant inks were developed to fabricate polysilicon thin film transistors (TFTs). Semiconductor-grade dopant inks were formulated from a combination of thermoset plastic with boron and phosphor compounds. Inks were screen printed on polysilicon active islands on a 300 mm square stainless-steel foil substrate. The drain and source of the top gate TFTs were then formed via a thermal anneal activation. The residue after annealing was removed with an inoffensive process to avoid damage to the thin silicon layer and gate oxide. Doping was uniform across 300 mm sheet substrate. The sheet resistance was modulated to 200 Ω sq−1 for the N+ and 1000 Ω sq−1 for the P+ active layer. Field mobility of polysilicon TFTs fabricated using this screen-printed dopant process were 80 cm2V s−1 for PMOS and 200 cm2V s−1 for NMOS using low-cost, mature equipment, and an easily manageable process that is both scalable and compatible with roll-to-roll manufacturing.

Fabrication, micro-structure characteristics and transport properties of co-evaporated thin films of Bi2Te3 on AlN coated stainless steel foils

N-type bismuth telluride (Bi2Te3) thin films were prepared on an aluminum nitride (AlN)-coated stainless steel foil substrate to obtain optimal thermoelectric performance. The thermal co-evaporation method was adopted so that we could vary the thin film composition, enabling us to investigate the relationship between the film composition, microstructure, crystal preferred orientation and thermoelectric properties. The influence of the substrate temperature was also investigated by synthesizing two sets of thin film samples; in one set the substrate was kept at room temperature (RT) while in the other set the substrate was maintained at a high temperature, of 300 °C, during deposition. The samples deposited at RT were amorphous in the as-deposited state and therefore were annealed at 280 °C to promote crystallization and phase development. The electrical resistivity and Seebeck coefficient were measured and the results were interpreted. Both the transport properties and crystal structure were observed to be strongly affected by non-stoichiometry and the choice of substrate temperature. We observed columnar microstructures with hexagonal grains and a multi-oriented crystal structure for the thin films deposited at high substrate temperatures, whereas highly (00 l) textured thin films with columns consisting of in-plane layers were fabricated from the stoichiometric annealed thin film samples originally synthesized at RT. Special emphasis was placed on examining the nature of tellurium (Te) atom based structural defects and their influence on thin film properties. We report maximum power factor (PF) of 1.35 mW/m K2 for near-stoichiometric film deposited at high substrate temperature, which was the highest among all studied cases.

A non-vacuum dip coated SiO2 interface layer for fabricating CIGS solar cells on stainless steel foil substrates

A novel solution processed SiO2 coating is investigated for use as an interface layer between the substrate and Mo back contact for making CIGS solar cells on flexible SS foils. Prior to deposition of Mo, a ~ 1 μm thick SiO2 layer is applied on commercially available SS foils using an economical non-vacuum dip coating method. CIGS absorbers as well as complete CIGS solar cells having the structure Mo/CIGS/CdS/i-ZnO/AZO are grown on SS foils with and without the interface layer and their characteristics are compared. The interface layer improves the adhesion and high temperature mechanical stability of Mo back contact. Although phase formation of CIGS absorber is not influenced by the presence of interface layer, the grain structure and surface morphology are positively impacted, resulting in an enhanced solar cell performance. Composition measurements did not reveal any increase of Fe content in the CIGS absorber after the high temperature selenization step. However, the role of interface layer in blocking the diffusion of Fe from the SS substrate is uncertain, as the high-quality Mo back contact itself could be acting as an efficient Fe barrier layer. The interface layer is capable of electrically isolating Mo back contact from the underlying SS substrate, thus offering the prospect of monolithic integration for making lightweight CIGS modules. With a simple and inexpensive deposition process, which can be easily upscaled for large substrates, the dip-coated SiO2 interface layer could be a suitable alternative for various existing vacuum deposited layers in realizing low-cost flexible CIGS modules.

V2O5 Film Embedded Carbon Fiber Paper Synthesized By Sol Process As Highly Pseudocapacitive Electrode for Energy Storage

In this work, by utilizing carbon paper having cress-crossing fibrous network structure as a template, high porosity crystalline V2O5 film electrode is synthesized using a simple sol precursor dip-dry-anneal method. Detailed cyclic voltammetry (CV), charge-discharge (CD) and impedance measurements were carried out in acetonitrile +LiClO4 electrolyte. CV data identify V5+/V4+ and V4+ /V3+ redox peaks which yield high specific capacitance of 800 Fg-1. These values are significantly higher compared with the similarly processed V2O5 over flat stainless steel (SS) foil substrate which proves the efficacy of carbon fiber paper for structuring V2O5 and in enhancing its specific capacitance. The CD data show high (>92%) Coulomb efficiency highly reversible redox reactions compared to the V2O5 film over SS. The major contributing factor was multifaceted access to electrolyte ions which enhances redox rates via charge transfer in response to electron injection or extraction via carbon fiber network.

Flexible, Thin-Layer Solid-State Supercapacitor Based on V2O5-Graphene Composite Electrode and Ionic Liquid Gel Polymer Electrolyte for Portable Electronic Systems

Electrochemical and energy storage properties of vanadium oxide-graphene composite electrode based solid state supercapacitor using ionic liquid gel electrolyte over flexible stainless-steel foil substrates are discussed. The composite electrode was deposited by a simple technique of spin coating of nano-size graphene dispersed vanadium sol gel followed 300°C -6h air annealing. Graphene mitigates the low electrical resistance limitation of faradaic V2O5 while contributing double layer capacitance to the overall pseudocapacitance. The BMIMBF4 ionic liquid gel with 0.2M LiClO4 dopant acts as high ionic conductivity electrolyte and source of counter ions for redox reactions. The flexible symmetrical V2O5/graphene supercapacitor shows high specific capacitance of 650 Fg-1 and energy and power density values of 30 Wh.kg-1 and 3kW kg-1, respectively at charging potential of 1.5V. The linear charge-discharge, high Coulomb efficiency ~90% and low internal resistance support its use as power source for portable electronics with high energy storage capability.

WITHDRAWN: Flexible, Thin-Layer Solid-State Supercapacitor Based on V2O5-Graphene Composite Electrode and Ionic Liquid Gel Polymer Electrolyte for Portable Electronic Systems

This abstract has been withdrawn at the request of the authors.

Optimizing the Structural, Electrical and Thermoelectric Properties of Antimony Telluride Thin Films Deposited on Aluminum Nitride-coated Stainless Steel Foil

In this study, we examined the thermoelectric (TE) properties of co-evaporated p-type antimony telluride (Sb2Te3) thin films on aluminum nitride (AlN)-coated stainless steel foil substrates. We investigated the influence of composition and substrate temperature on the thin-film microstructure and transport properties, by varying the tellurium (Te) concentration in the thin films as well as the substrate temperature during deposition (room temperature (RT) and 300 °C). Thin films prepared with an RT substrate were further annealed at 264 °C to obtain crystallized thin films with high phase purity. Columnar thin films with large grains and a standard multi-oriented crystal structure were obtained when thin films were deposited on substrates heated to 300 °C. Thin films deposited at RT and subsequently annealed at 264 °C had a dense, layered microstructure, with a preferential c-axis or (00 l) texture as the compositions approached phase stoichiometry. The temperature dependence of the thermoelectric properties was measured, and variations were interpreted in terms of the deviation from stoichiometry and the obtained microstructure. A maximum power factor (PF) of 0.87 mW/m ∙ K2 was obtained for off-stoichiometric 65.0 at% Te thin film, which was the highest among the samples deposited at high substrate temperatures. A higher PF of 1.0 mW/m ∙ K2 was found for off-stoichiometric thin films with 64.5 at% Te, which was deposited at RT and subsequently annealed. The improvement of thermoelectric power in films containing excess Te could be related to energy dependent carrier scattering at the Sb2Te3/Te interface.

Cu(In,Ga)Te2 film growth by a two-stage technique utilizing rapid thermal processing

Cu(In,Ga)Te2 (CIGT) thin films doped with Na were grown using a two-stage technique. During the first stage of the process precursor layers were formed over Mo coated stainless steel foil substrates by electrodeposition of Cu, In and Ga and evaporation of a NaF film as a dopant and Te. During the second stage, the foil/Mo/(Cu, In, Ga)/NaF/Te stacks were reacted by rapid thermal processing. The ramp rate to the reaction temperature of 600 °C was changed between 0.5 and 10 °C s−1. Resulting compound layers were analyzed to evaluate the effect of the temperature ramp rate on film quality. It was found that a secondary phase of InTe that was detected in films reacted at ramp rates of 0.5–5 °C s−1 was not present for the films reacted at a ramp rate of 10 °C s−1. Film morphology of the fast ramp rate sample showed improved crystallinity and grain size, which was superior compared to others. Gallium gradation was detected through all the layers irrespective of the temperature ramp rate, surface of the films being more In-rich.

Seed-induced synthesis of flower-like a Li3V2(PO4)3/carbon composite and its application in lithium-ion batteries

Uniform, flower-like Li3V2(PO4)3/C composites were successfully synthesized using a novel, seed-induced method and were then directly applied as a cathode in lithium-ion batteries. The morphology, structure and electrochemical properties of these novel composites were examined using X-ray diffraction, scanning electron microscopy and galvanostatic charge-discharge tests. The uniform, flower-like Li3V2(PO4)3/C composites were produced on stainless steel and titanium foil substrates, but the morphology of the flowers depended on the type of substrate and the method of immersion. The Li3V2(PO4)3/C composites grown on the stainless-steel substrate exhibited the best electrochemical performance with a specific capacity of 115 mAh g−1 at the 15 C rate and a capacity retention of 94% after 500 cycles. This remarkable electrochemical performance was attributed to the formation of the perfect flower-like structure and abundance of pores in the composite. The seed-induced method proved to be a promising approach for preparing electrode materials for use in lithium ion batteries.

Cu(In,Ga)(Se,Te)2 films formed on metal foil substrates by a two-stage process employing electrodeposition and evaporation

Cu(In,Ga)(Se,Te)2 or CIGST films were grown over molybdenum coated stainless steel foil substrates using a two-stage technique. The process involved deposition of a Cu-In-Ga/Se-Te precursor stack over the Mo layer using electrodeposition for the metals and evaporation for the chalcogens. The stack was then annealed at 600 °C to initiate reaction between the constituent elements. The reacted films were characterized in terms of their structural, compositional, electrical and optical properties. Results were compared to films obtained using all-evaporated precursor stacks formed on glass substrates. It was observed that the compositional control and the morphological properties of the compound layers grown on the metal foil substrates employing electrodeposition and rapid thermal annealing were superior to the films obtained on glass substrates using evaporated precursors and slower temperature ramp rate during annealing. Glancing angle XRD measurements at the front and back surfaces of the layers showed that Ga distribution through the CIGT films was much more uniform than that through the CIGS layers. CIGST films, which contained both Se and Te had slightly Se-rich surface compared to their bulk.

Non-aqueous electrochemical deposition of lead zirconate titanate films for flexible sensor applications

Lead zirconate titanate (PZT) is one of the most important piezoelectric materials widely used for underwater sensors. However, PZTs are hard and non-compliant and hence there is an overwhelming attention devoted toward making it flexible by preparing films on flexible substrates by different routes. In this work, the electrochemical deposition of composition controlled PZT films over flexible stainless steel (SS) foil substrates using non-aqueous electrolyte dimethyl sulphoxide (DMSO) was carried out. Effects of various key parameters involved in electrochemical deposition process such as current density and time of deposition were studied. It was found that a current density of 25 mA/cm2 for 5 min gave a good film. The morphology and topography evaluation of the films was carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively, which showed a uniform morphology with a surface roughness of 2 nm. The PZT phase formation was studied using X-ray diffraction (XRD) and corroborated with Raman spectroscopic studies. The dielectric constant, dielectric loss, hysteresis and I–V characteristics of the film was evaluated.

Piezoelectric characterization of Pb(Zr,Ti)O3 thin films deposited on metal foil substrates by dip coating

We fabricated the piezoelectric bimorphs composed of Pb(Zr,Ti)O3 (PZT) thin films on metal foil substrates. To efficiently inexpensively manufacture piezoelectric bimorphs with high flexibility, 1.2-µm-thick PZT thin films were directly deposited on both surfaces of 10- and 20-µm-thick bare stainless-steel (SS) foil substrates by dip coating with a sol–gel solution. We confirmed that the PZT thin films deposited on the SS foil substrates at 500 °C or above have polycrystalline perovskite structures and the measured relative dielectric constant and dielectric loss were 323–420 and 0.12–0.17, respectively. The PZT bimorphs were demonstrated by comparing the displacements of the cantilever specimens driven by single- and double-side PZT thin films on the SS foil substrates under the same applied voltage. We characterized the piezoelectric properties of the PZT bimorphs and the calculated their piezoelectric coefficient |e31,f| to be 0.3–0.7 C/m2.

Role of the precursor chemistry on the phase composition and electrochemical performance of thin-film LiMn2O4 Li-ion battery cathodes prepared by spray pyrolysis

LiMn2O4-films were prepared by air-blast spray pyrolysis directly onto stainless steel foil substrate. The films were synthesized from various precursor solutions of dissolved nitrates and acetates with and without the addition of polyethylene glycol (PEG). Hereby X-ray diffraction experiments revealed that the phase compositions of the as-prepared and thermally post-treated films were highly dependent on the precursors used, but independent of the addition of PEG. Samples prepared from nitrates yielded phase mixtures of α-Mn2O3, Mn3O4 and LiNO3 as-prepared and LiMn2O4 and α-Mn2O3 after post-thermal treatment. Whereas films sprayed from acetate precursors consisted of LiMn2O4 predominantly before and after heat treatment, as well. Scanning electron microscopy investigations showed that the applied precursor had an effect on the film morphology and the addition of PEG led to film thinning. Galvanostatic cycling tests and post-mortem analyses of the electrochemical cells fabricated from the thermally treated thin layers revealed that the film prepared from acetates and PEG had the highest capacity retention despite the formation of orthorhombic LiMnO2 besides the cubic LiMn2O4 during battery cycling.

Thermo-oxidation of laboratory-produced undoped and W-doped carbon films: A reaction product analysis

Thermo-oxidation is a technique where O2 gas is used to remove carbon co-deposits at elevated temperatures from plasma-facing materials of fusion devices. Following thermo-oxidation, the reaction products produced will need to be managed by a reactor's gas-handling system, including the tritium plant. Thus, it is important to know what molecular species are produced during oxidation. The reaction products of thermo-oxidation have previously been studied for undoped films indicating CO, CO2 and D2O as the reaction products. The present study directly compares the reaction product evolution of undoped films to that of films doped with tungsten.A glow discharge was used to produce sets of undoped and W-doped films on stainless steel (SS) foil substrates. X-ray photoelectron spectroscopy (XPS) found the W-doped films to contain an average 0.1 at.% W/(W+C). Laser thermal desorption spectroscopy (LTDS) was used to measure the areal D-concentration. Reaction products during oxidation were measured using a quadrupole mass spectrometer (QMS). Both the undoped and W-doped specimens were oxidized in 2Torr O2, at 350 °C for 4h, total. LTDS was then used to determine how much D had been removed during oxidation (93% and 32% of the D was removed after oxidation for the undoped and W-doped cases respectively). The reduced D loss for the W-doped specimens is attributed to a change in film structure due to the incorporation of W in the film. Oxidation reaction products for both undoped and W-doped films include CO, CO2, and D2O, with no finding of D2 or CD4 within experimental uncertainty. Particle accounting was performed for oxygen, deuterium and carbon atoms.

Considerations and Methodology to Determine R2R Manufacturing and Scaling of Electronic Devices on Flexible Stainless Steel Foil Substrates

ABSTRACTStainless steel substrates enable a combination of low cost, flexibility, durability, high processing temperatures, and sub-100 um thickness making it well suited for sheet based and roll-to-roll processing. NFC (13.56 MHz) based circuits using high performance polysilicon TFTs on steel sheets have been manufactured using a hybrid printed process in a production environment. The process scheme utilizes a hybrid, additive materials approach encompassing low cost manufacturing steps such as slot die coating and screen printing of silicon and dopant inks to enable a high throughput, low cost, manufacturing flow. This paper describes the approach for migrating from a sheet-based hybrid process flow to a R2R-based process. A comparison of substrate choices and considerations for R2R process integration is presented. A sensitive electrical method for evaluating the feasibility of R2R-based process integration schemes and materials selection is presented. MIM capacitor leakage, TFT device characteristics, NFC circuit performance, and defect density considerations are shown as a function of steel substrate bending, down to a diameter of 0.75 inches. Electrical characteristics and optical inspections show no measurable change to insulator characteristics, demonstrating a high degree of flexibility and overall device and process capability for R2R processing.