Flexible Stainless Steel Substrate Research Articles

Electrochemical engineering approach of high performance solid-state flexible supercapacitor device based on chemically synthesized VS2 nanoregime structure

Abstract Portable and furnished electronics appliances demand power efficient energy storage devices where electrochemical supercapacitors gain much more attention. In this concern, a simple, low-cost and industry scalable successive ionic layer adsorption and reaction (SILAR) approach has been adopted to deposit nanostructured VS2 onto flexible and light-weight stainless steel (SS) substrate towards supercapacitor application. The nanocrystalline nature with hexagonal crystal structure has been confirmed for VS2 through structural analysis. The VS2 electrode exhibits a maximum specific capacitance of 349 F g−1 with a super stable behavior in three-electrode liquid-state configuration. Fabricated flexible symmetric solid-state supercapacitor (FSSC) device using gel electrolyte yields specific power of 1.5 kW kg−1 (specific energy of 25.9 Wh kg−1) with a widen voltage window of 1.6 V. A red LED has been glown for 30 s using the system consisted of two devices in series combination. Furthermore, the system glows a combination of 21 red LEDs network with acronym ‘VNIT’, demonstrating commercial exposure. The attribution of device demonstration even under mechanical stress holds great promise towards advanced flexible electronics application.

Development of flexible Cd-free Cu(In,Ga)Se2 solar cell on stainless steel substrate through multi-layer precursor method

Cu(In,Ga)Se2 (CIGS) absorbers on flexible stainless steel (SUS) substrates in thin-film solar cells are deposited by multi-layer precursor method with different [Ga]/([Ga]+[In]) grading profiles, thus yielding different band-gap energy (Eg) grading profiles. In Eg grading profiles, near-surface Eg is defined as average Eg within 200 nm from CIGS surface, and minimum Eg is the lowest Eg. It is disclosed that near-surface Eg and minimum Eg have impacts on open-circuit voltage and short-circuit current density, respectively. 17.6%-efficient CIGS solar cell on flexible SUS substrate using CdS buffer is obtained with the suitable Eg grading profile consisting of near-surface Eg and minimum Eg of 1.26 and 1.08 eV, respectively. Flexible Cd-free CIGS solar cell on SUS substrate using ZnS(O,OH) buffer is next fabricated with relative low conversion efficiency of 8.5%, attributed to a relatively low Zn diffusion into CIGS and/or the large conduction band offset (CBO) at ZnS(O,OH)/CIGS interface. However, all photovoltaic parameters of the Cd-free CIGS solar cell are improved after light-soaking process owing to improvement of the CBO at ZnS(O,OH)/CIGS interface. Ultimately, 14.8%-efficient Cd-free CIGS solar cell on flexible SUS substrate utilizing ZnS(O,OH) buffer is obtained, thereby demonstrating the ability for portable power source.

Flexible kesterite Cu2ZnSnS4 solar cells with sodium-doped molybdenum back contacts on stainless steel substrates

In this work we report the Na incorporation from Na-doped Mo (Mo-Na) back contact for kesterite Cu2ZnSnS4 solar cells on flexible stainless steel substrates. It is demonstrated that Na can be effectively incorporated into CZTS by inserting Mo-Na layer at back contact. Direct contact of CZTS and Mo-Na layer leads to poor homogeneity and adhesion. The thickness of MoS2 formed at the back contact depends on the presence of Na and whether Mo contacts with CZTS directly. Back contact configuration with a Mo capping layer on Mo-Na layer is found to be helpful to maintain the advantages of Mo back contact and control the thickness of MoS2 interface. As a result, CZTS device fabricated on this configuration yields higher conversion efficiency of 6.2%. However, this efficiency is still far lower than that on traditional soda lime glass substrate which shows efficiency over 8%. The loss mechanism of device fabricated on stainless steel is investigated and analyzed according to the device performance and electrical parameters.

Al:ZnO Nanosheets on Flexible Stainless Steel Substrate as Impact Sensor

We report the fabrication of impact sensor on flexible stainless steel substrate (SS 304) based on Al:ZnO nanosheets and Polydimethylsiloxane (PDMS) nanocomposite film. Synthesis of Al:ZnO nanosheets are carried out by hydrothermal method at lower temperature (90 °C) on Al alloy substrate without Al dopants. PDMS polymer is prepared by mixing of curing agent and base (Silicone Elastomer, Sylgard 184) in the ratio of 10:1 respectively. For the fabrication of impact sensor, a mixer of PDMS (1 gm) and Al:ZnO nanosheets (0.1 gm) are used for making the nanocomposte film. The mixture of nanocomposite solution was spin coated (500 RPM with 60 Sec) over the flexible stainless steel (diameter of 25 mm) substrate, subsequently kept the film at 85 °C for 2 hrs. The cured nanocomposite film is sandwich between Au coated substrates along with the necessary electrical leads. The maximum output response obtained from the fabricated Al:ZnO nanosheets and PDMS nanocomposite film based impact sensor is about 4.45 V with fast finger impacts. Various finger impacts (slow, medium and fast, force in the range of 50 to 120 gms) showed the maximum output responses of 2.01, 3.19 and 4.45 V respectively. The variations in the magnitude (speed) of finger impacts suggest the possible use of developed sensor for impact as well as speed sensing applications. In addition, the overall output response of the nanocomposite sensor can be used for energy harvesting applications as a power source in ultra low power devices. It can also be used in flexible and stretchable device applications include touch sensor, e-skin, personal healthcare and biomedical applications.

Decoration of Ultrathin MoS2 Nanoflakes over MWCNTs: Enhanced Supercapacitive Performance through Electrode to Symmetric All‐Solid‐State Device

AbstractUltrathin nanoflakes surface architecture of MoS2 thin film has been successfully decorated by simple and inexpensive chemical bath deposition onto dip and dry coated multiwalled carbon nanotubes (MWCNTs) to compare electrochemical performance with respect to individual MWCNTs and MoS2 thin films on flexible stainless steel (SS) substrates. Two dimensional thin films of MWCNTs, MoS2 and MoS2/MWCNTs (MCT) have been characterized through X‐ray diffraction, X‐ray photospectroscopy, Raman spectroscopy and scanning/transmission electron microscopes. The unique nanostructured morphology of well anchored nanoflakes over MWCNTs enhances the value of specific capacitance and improves the cycle stability compare to bare MoS2. Strikingly, all‐solid‐state (ASS) symmetric SS/MCT//MCT/SS supercapacitor device has been constructed using flexible stainless steel substrate with the aid of PVA‐LiClO4 gel electrolyte and results are discussed herein.

Electrolytic anion affected charge storage mechanisms of Fe3O4 flexible thin film electrode in KCl and KOH: a comparative study by cyclic voltammetry and galvanostatic charge–discharge

Effect of electrolytic anions on the charge storage mechanism and hence on the specific capacitance of Fe3O4 (magnetite) flexible thin film electrodes (FTFEs) has been studied. The synthesis of Fe3O4 on flexible stainless steel substrates has been carried out using successive ionic layer adsorption and reaction technique. 0.2 M FeCl3 and 0.1 M NaOH aqueous solutions were used as cationic and anionic sources respectively. X-ray diffraction pattern of the FTFE shows peaks at angles 2θ = 43.64° and 44.54° indicating the formation of orthorhombic Fe3O4 crystals of average size 10.25 nm. The scanning electron microscopic (SEM) image of FTFE shows irregularly stacked thin layers of interconnected nanograins. Surface wettability investigation concluded the hydrophilic nature of the prepared electrodes, as the measured contact angle was 10.5°. Thickness of the thin film observed by SEM cross section is ~267 nm. Cyclic voltammetric (CV) analyses substantiated that depending on the existence of electrolytic anion, the electrode stores charge either by physisorption-desorption or by redox reactions. FTFE shows maximum current hence the specific capacitance in KOH is more than SC in KCl. The observed maximum specific capacitance (SC) in 1 M aqueous solution of KCl was 206.53 F g−1 and that in 1 M aqueous solution of KOH was 542.21 F g−1 at 100 mV s−1. The galvanostatic charge–discharge analyses shows that the electrochemical performance of FTFE in KOH is better than that in KCl. The observed values of SCs at current density 1 mA cm−2 in KCl and KOH were 281.22 and 487.84 F g−1 respectively, which are nearly same as those given by the CV.

Electrochemically synthesized mesoporous architecture of vanadium oxide on flexible stainless steel for high performance supercapacitor

Mesoporous architecture of vanadium oxide thin films were successfully synthesized on flexible stainless steel substrates [SS (1.5 × 5 cm, no- 304)] at 2.30 V deposition potential by potentiostatic electrodeposition technique using 0.007 M, 20 ml aqueous solution of vanadyl sulphate. Electrochemical properties of electrodeposited V2O5 electrodes were analyzed by cyclic voltammetry, chronopotentiometric charge discharge and electrochemical impedance in 1 M aqueous KCl electrolyte. The annealed vanadium oxide electrode (400 °C for 3 h) shows highest value of specific capacitance 608.94 F/g at 5 mV/sec in 1 M KCl. Charge discharge behavior exhibits high reversibility with specific energy 63.73 Wh/kg, specific power146.66 kW/kg and columbic efficiency (η) 94.97%. Impedance spectroscopy reveals capacitive behavior and gives combined internal resistance ~1.53 ohm.

Ge quantum dot enhanced hydrogenated amorphous silicon germanium solar cells on flexible stainless steel substrate

Ge quantum dots (QDs) have been applied to increase the internal quantum efficiency (IQE) of photodetector up to 1500% at the 400nm and are expected to benefit the performance of solar cell. We have successfully prepared Ge-QDs using plasma enhanced chemical vapor deposition (PECVD) that is fully compatible with the solar cell deposition process. Transmission electron microscope (TEM) and Atomic force microscope (AFM) images show that the QDs are ∼14nm in diameter. By adjusting deposition time, as well as H2 dilution ratio and H2-plasma treatment time, the Ge-QDs are optimized for the highest solar cell efficiency. It is found that the IQE is significantly improved, particularly for long wavelength spectrum (λ>500nm), resulting in increased short circuit current density (Jsc) by 8.31% and increased solar cell efficiency.

Synergistic effect between redox additive electrolyte and PANI-rGO nanocomposite electrode for high energy and high power supercapacitor

Supercapacitors (SCs), as high power density energy storage resources, have recently attracted considerable attention. Increasing the energy of supercapacitors is a key parameter to success in achieving far more demanding energy storage applications. There are two approaches to achieve this goal: the first is to widen the operating potential window, and the second is to develop emerging capacitive or pseudocapacitive materials. Polyaniline (PANI) with different morphologies, and hence different supercapacitive performances, has been considered as one of the intriguing active materials due to its high conductivity, intrinsic flexibility, and high redox active specific capacitance. In this work, we report on a simple and convenient method to synthesize PANI nanotubes with rectangular morphology. Then we synthesized PANI/reduced graphene oxide (PANI-rGO) nanocomposite via a convenient electrochemical reduction process. We investigated electrochemical performance of the electrode in the presence and absence of catechol, as a redox-additive molecule incorporated into the electrolyte, by CV, EIS and GCD methods. With incorporation of the catechol in the electrolyte the operating potential window of the electrode increased from 1.0 to 1.2V, and its capacitance boosted about 5-fold from 429 to 1967F/g at a current density of 1A/g. The astonishing supercapacitive performance of the electrode is attributed to; (i) the rectangular nanotube morphology of the PANI, which provides both a better electrical conductivity and a facilitated ion transport pathway, and (ii) the synergetic effect between PANI-rGO and catechol. The electrode showed a superior long cycle life with 81% retention of the initial specific capacitance after 5000 cycles, and demonstrated an excellent rate capability with specific capacitances of 267 and 546F/g, at a current density of 20A/g, in the absence and presence of catechol, respectively. Furthermore, we fabricated a symmetric device using the PANI-rGO film on a flexible stainless steel substrate in the catechol-containing electrolyte. The device showed specific capacitance of 409F/g at 1A/g, energy density of 81.8Wh/kg and power density of 7.7kW/kg. These findings could be beneficial for further development of diverse energy storage devices and open up new prospects for the fabrication of high energy and power supercapacitors.

Structural, optical, and electrical-transport properties of Al-P-O inorganic layer coated on flexible stainless steel substrate

We coated inorganic layer containing oxygen, aluminium, phosphorus, and negligible sodium (APO) on stainless steel (STS) by using slot-die coating method and studied its application prospects as a substrate for flexible devices. The APO layer was compositionally uniform in overall area with an amorphous crystal structure. Surface morphology characterization of STS exhibited an improved flatness after the APO layer coating process. The optical property characterization of the APO film carried out by measuring optical reflectance spectrum and refractive index. We also investigated the electrical-transport mechanism in the APO layer. These experimental observations imply the possibility of potential application of APO-STS as a substrate for flexible devices.

Structural evolution of nanocrystalline silicon in hydrogenated nanocrystalline silicon solar cells

We deposited hydrogenated nanocrystalline silicon (nc-Si:H) thin films and n-i-p solar cells onto flexible stainless steel substrates through the plasma-enhanced chemical vapor deposition (PECVD) method to investigate the effects of n-doped layers with different crystallinity on the structural evolution of the subsequent intrinsic nc-Si:H layers. The n-doped layers with various crystalline volume fractions were formed by changing the hydrogen dilution ratios. The structural characteristics of the nc-Si:H thin films were tested using transmission electron microscopy (TEM) and Raman scattering measurements. Intrinsic nc-Si:H layers, with an incubation layer up to 200nm, were observed deposited on low crystallinity n-doped layers during the initial growth stage. Increasing the crystallinity of n-doped layers helps reduce the thickness of the incubation layers at the n/i interface and improves the microstructure homogeneity of i-layers. The experimental results demonstrate that the short circuit current density and fill factors of solar cells can be greatly improved by adopting high-crystallinity n-doped layers. This is mainly a result of the enhancement of photo-induced carrier transport properties. The n-i-p solar cells with high-crystallinity n-layers exhibited 25% higher conversion efficiency than those with amorphous n-layers.

Influence of minimum position in [Ga]/([Ga]+[In]) profile of Cu(In,Ga)Se2 on flexible stainless steel substrate on its photovoltaic performances

Cu(In, Ga)Se2 (CIGS) solar cells on stainless steel (SUS) substrates are fabricated with various [Ga]/([Ga]+[In]), GGI, profiles in their absorbers. From GGI profiles, near-surface GGI is defined as average GGI within 200nm from CIGS surface, mini GGI value is the lowest GGI, and mini GGI position is a distance between the lowest GGI position and CIGS surface. These are used as representatives of the GGI profile. Their impacts on cell performances are quantitatively examined. It is revealed that near-surface GGI is optimized in a range of approximately 0.40–0.45 (or band-gap energy of 1.28–1.30eV), resulting in improvement of conduction band offset at CdS/CIGS interface. From simulation, optimized mini GGI position is in a range of 250–350nm, well consistent with space charge region width. According to experimental results, fill factor and open-circuit voltage are increased when mini GGI position is decreased from 1.1 to 0.4µm, while short-circuit current density is increased with decreasing mini GGI value. Ultimately, 17.3%-efficient CIGS solar cell on flexible SUS substrate with thin CIGS thickness of 1.5µm is achieved, where near-surface GGI, mini GGI position, and mini GGI value are 0.42, 0.5µm, and 0.06, respectively.

Formation process and photovoltaic properties of Cu(In,Ga)Se2 and (Ag,Cu)(In,Ga)Se2 on flexible stainless steel substrates formed at different selenization temperatures

Cu(In,Ga)Se2 (CIGS) and (Ag,Cu)(In,Ga)Se2 (ACIGS) films were successfully fabricated on stainless steel substrates using the non-vacuum spin-coating process followed by the selenization process. As the selenization temperature was increased to 550 °C, the Voc, Jsc, FF, and conversion efficiency of both CIGS and ACIGS solar cells were enhanced. On selenization at temperature above 550 °C, the morphology of the CIGS films become angular shape, and porous microstructures were formed. EDS and SIMS analyses revealed that the iron ions were substantially diffused from stainless steel substrates into the CIGS absorber layers. The existence of iron ions in CIGS thin films resulted in formation of short circuits of CIGS solar cells, thereby dropping the conversion efficiency of solar cells to zero. On the other hand, the efficiency of ACIGS was higher than that of CIGS solar cells owing to the high band gap and densified thin films. In addition, adding silver ions to the absorber layers effectively enhanced the stability of ACIGS thin films during high-temperature selenization, and suppressed the interaction between the absorber layers and iron ions. This research reveals that the incorporation of silver ions to form ACIGS improved the conversion efficiency at low selenization temperatures, and enhanced the stability of ACIGS films at high selenization temperatures.

Electrical Characteristics of Top-Gated Graphene Field Effect Transistors Fabricated on Stainless Steel (STS) Substrate.

Top-gated Graphene transistors with Al2O3 gate-dielectric on the flexible stainless steel substrate have been demonstrated. Graphene was synthesized on copper foil using a chemical vapor deposition method and transferred onto the stainless steel substrate by wet transfer technique. The stainless steel substrate was polished by chemical mechanical polishing method and the spin-on-glass layer was coated on the surface to improve the surface roughness. The average surface roughness R(a) was as low as 5.9 nm from the AFM measurement. The measured hole and electron mobilities from the current-voltage characteristics at room temperature were calculated as high as 310 and 45 cm2/Vs, respectively. In addition, the effect of surrounding temperature up to 355 K on the electrical variations was investigated. The mobility was inversely proportional to the temperature with negligible hysteresis where the temperature coefficient was calculated as low as -0.65 %/K.

30×40 cm2 flexible Cu(In,Ga)Se2 solar panel by low temperature plasma enhanced selenization process

A progressing non-toxic plasma-enhanced solid Se vapor selenization process (PESVS) technique, compared with hydrogen-assisted Se vapor selenization (HASVS) to achieve a large-area (30×40cm2) Cu(In,Ga)Se2 (CIGS) solar panel with enhanced efficiencies from 10.8% to 13.2% (14.7% for active area), was demonstrated. The bonding of Se was partially broken by ICP plasma treatment and these Se radicals are helpful to enhance reaction activity for following selenization process at an extremely low temperature of 330°C. The effects of plasma steps, plasma power, selenization temperature and optimized conditions were thoroughly studied in detail. The remarkable enhancement of the efficiency is ascribed to the better crystallinity, enlarged grain size, less Se vacancy and uniform depth distribution of Ga. From reaction kinetics point of view, PESVS provides extra energy to crack Se, resulting in the decrease in reaction activation energy. The PESVS methodology was also applied to low temperature (450°C) selenized CIGS thin film solar panel with uniform conversion efficiency more than ~10%. Furthermore, a large-area flexible stainless steel substrate with remarkable conversion efficiency of ~6.8% without Na addition was demonstrated. We believed that this work can provide a facile approach of low temperature selenization on flexible substrate applications or fast selenization for throughput consideration, thus stimulating the mass-production in large scale CIGS PV industry.

Substrate temperature optimization for Cu(In, Ga)Se2 solar cells on flexible stainless steels

Cu(In, Ga)Se2 (CIGS) thin films are deposited on flexible stainless steel (SS) substrates using the so called 3-stage co-evaporation process at different substrate temperatures ranging from 440°C to 640°C during the 2nd stage and the 3rd stage (TS2). The effects of TS2 on the properties of CIGS thin films are systematically investigated. It is found by secondary ion mass spectrometry measurement that CIGS thin films deposited at different TS2 show different Ga/(Ga+In) ratio (GGI) profiles along the growth direction. High TS2 facilitates the grain growth and leads to larger grain size. However, high TS2 worsens the spectral response of CIGS solar cells in the long wavelength range, which is partly attributed to the too much iron atom diffusion from the SS substrates into the CIGS thin films. All CIGS thin films show (112) preferred orientations with a shift to higher angle due to variation of compositions. A shoulder-like two-peak structure of (112) and (220/204) peaks appears for CIGS thin films deposited at lower TS2. Conversion efficiency of 11.3% is obtained for CIGS thin film solar cells deposited at the TS2 of 500°C.

电化学机械复合抛光薄膜太阳能电池柔性不锈钢衬底

电化学机械复合抛光薄膜太阳能电池柔性不锈钢衬底

Double-layered Ag–Al back reflector on stainless steel substrate for a-Si:H thin film solar cells

An effective light trapping method for substrate-type hydrogenated amorphous silicon (a-Si:H) thin film solar cells is the use of a back reflector (BR) of high roughness, e.g., ‘hot silver’, which is deposited at temperatures higher than 450°C. In this work, textured silver-aluminum (Ag–Al) BR films were fabricated by depositing Ag on Al film at Ag-deposition temperatures (TAg) ranging from 25 to 350°C. The surface morphology and roughness of Ag–Al films were strongly affected by TAg. The Al and Ag films were formed entirely of Ag2Al alloy at TAg of 330°C or higher, while the Ag–Al films maintained a double-layered structure at 290°C or below. Although the films did not undergo alloying at TAg of 290°C, the Ag–Al films have a well-developed surface structure with high diffuse-reflectance, compared to Ag films deposited at the same temperature. The conversion efficiency of an a-Si:H thin film solar cell on a flexible stainless steel substrate increased from 7.63% to 8.44% as TAg was increased from 25 to 290°C, as a result of more effective light scattering by Ag–Al BRs, producing increased short-circuit current. However, at higher TAg, Ag2Al alloy films with sharp crystallite edges were formed, and were not appropriate as BRs. The present work clearly shows that double-layered Ag–Al films fabricated at temperatures as low as 290°C could be useful back reflectors for substrate-type thin film solar cells.

Electrical insulation and breakdown properties of SiO2 and Al2O3 thin multilayer films deposited on stainless steel by physical vapor deposition

The electrical properties of dielectric thin layers deposited on conducting substrates still need to be thoroughly characterized for a wide variety of applications such as solar modules, flexible displays and sensor integration. In this work, thin dielectric films composed of layers and alternated multilayers of SiO2 and Al2O3 up to a total thickness of 3μm have been deposited on flexible rough stainless steel substrates by means of reactive magnetron sputtering. Their electrical properties have been studied focusing on important parameters such as leakage current density and disruptive field strengths. Moreover, temperature annealing and bending effects have been quantified. It is concluded that the best electrical properties with this type of materials are achieved with multilayered structures.

Physical properties of Cu(In,Ga)Se2 film on flexible stainless steel substrate for solar cell application: A multi-layer precursor method

The process named “multi-layer precursor method”, consisting of Ga–Se/In–Se/Cu–Se stacked precursors, is proposed to prepare Cu(In,Ga)Se2 (CIGS) films on flexible stainless steel (SUS) substrates. In this work, precursor deposition temperature (TPRE), varying from about 250 to 430°C, is first scrutinized. From Raman scattering measurement, it is suggested that the increase in the TPRE enhances Cu2−xSe secondary phase during film deposition, thus enlarging CIGS grain size, while decreases ordered vacancy compound (OVC) near surface of the finished film, caused by desorption of In2Se during the precursor deposition. Suitable TPRE is in a range of approximately 370–400°C, resulting in long carrier lifetime. Next, according to the examinations of material compositions of CIGS absorbers, the optimized [Cu]/([In]+[Ga]) contributes to the absorbers with large grain size due to the help of Cu2−xSe phase during film deposition and OVC near their surfaces for pn homo-junction. The appropriate [Ga]/([In]+[Ga]) leads to optimized band-gap energy with high CIGS quality implied by long carrier lifetime. Ultimately, the effective [Cu]/([In]+[Ga]) and [Ga]/([In]+[Ga]) ratios for the flexible CIGS solar cell with high conversion efficiency under the so-called “multi-layer precursor method” are in ranges of about 0.74–0.84 and 0.28–0.35, respectively.