Enhancement Of Current Density Research Articles

Well performing Fe-SnO2 for CO2 reduction to HCOOH

The climate change imposes to mankind a severe management of CO2 emissions in atmosphere. CO2 valorization through electrocatalysis revealed to be a valuable solution to this global issue. SnO2 is an electrocatalyst widely investigated for its capability to reduce CO2 to formic acid. In particular, mesoporous SnO2 offers a high adsorption capability, resulting in a high catalytic activity. In order to improve its performance, Fe-doping is here investigated for the first time. We observed that Fe-doped SnO2 exhibits a remarkable 100% enhancement of the partial current density for HCOOH production at relatively low overpotentials, although keeping the selectivity unchanged.

Critical current improvement and resistance evaluation of superconducting joint between Bi2223 tapes

We improved the critical current (I c) of the superconducting joint between the Bi2223 tapes by introducing the two-step sintering process. The in-field transport I c of ∼300 A at 4.2 K and 1 T under a 10−9 Ω criterion was successfully demonstrated. The I c improvement can probably be attributed to the enhancement of the intergrain critical current density for a Bi2223 intermediate layer. Ultra-low in-field joint resistance below 10−14 Ω at 4.2 K and 1 T was also demonstrated using current decay measurement. To the best of our knowledge, this study is the first to demonstrate a practical level of in-field transport I c and ultra-low in-field joint resistance for the superconducting joint between Bi2223 tapes. We believe that this superconducting joint technology will facilitate development of persistent current mode Bi2223 superconducting magnets.

Expediting hole transfer via surface states in hematite-based composite photoanodes.

Regarding the indirect hole transfer route in hematite-based photoelectrodes, the widely accepted viewpoint is that the FeIVO states act as a hole transfer medium, while other types of surface states act as recombination centers. Alternatively, it has rarely been reported that the recombining surface states may contribute to the charge transport in modified photoelectrodes. In this study, we employed CoCr layered double hydroxide (LDH)/Fe2O3 and CoCr LDH/Zr:Fe2O3 as research models to investigate the distinct charge transfer pathways in composite photoanodes. Different from the adverse role of surface states at ∼0.7 V versus the reversible hydrogen electrode (r-SS) in the bare hematite photoelectrodes (Fe2O3 or Zr:Fe2O3), the r-SS in the composite photoanodes (CoCr LDH/Fe2O3 or CoCr LDH/Zr:Fe2O3) served as a hole transfer station to induce high-valent Co cations, and the position of r-SS determined the onset potential of the composite photoelectrodes. Moreover, the FeIVO states still acted as active intermediates to transport numerous holes to the cocatalyst, which enhanced the charge utilization efficiency at 1.23 V versus the reversible hydrogen electrode (RHE) to a large extent. Besides, a noteworthy fact is that Zr doping increased the number of active FeIVO states, which significantly contributed to the enhancement in current density. However, it led to a delayed onset potential because of the positively shifted surface states (r-SS and FeIVO). Evidently, the different surface state distributions between Fe2O3 and Zr:Fe2O3 gave rise to anisotropic charge transfer and recombination behavior in the composite photoanodes. This study gives extensive insight into the hole transfer route in composite photoanodes and reveals the surface state-tuning effects of dopants and cocatalysts, which are significant for a deep understanding of the surface states and optimal design of composite photoanodes via surface state modulation.

Competition between ferromagnetism and superconductivity in GdBa2Cu3O7-x/La0.7Sr0.3MnO3 bilayers with varying thickness

We investigated the effect of the thickness of superconducting layer on the competition between ferromagnetism and superconductivity. The epitaxial bilayer systems consisting of GdBa 2 Cu 3 O 7-x (GdBCO) with varying thickness and La 0.7 Sr 0.3 MnO 3 (LSMO) were grown on (001) SrTiO 3 (STO) substrate. From the spectroscopic measurements, we observed an existence of a possible structural coupling between the GdBCO and the LSMO layers. The structural coupling is found to depend on the GdBCO thickness and to induce different types of strain on both layers, leading to the competition between the ferromagnetic and the superconducting orders. With respect to the flux pinning, an additional pinning contribution besides magnetic pinning induced by LSMO is emerged by the structural coupling, which is attributed to local atomic disorder. Controlling the thickness of GdBCO modifies the structural coupling and consequently, the degree of additional pinning contribution aroused by disorder on the CuO 2 plane can be adjusted. An appropriate structure with a certain thickness amplifies the hybrid effect of magnetic pinning and additional pinning, resulting in an enhancement of the critical current density at high magnetic fields. Our findings suggest a possibility of controlling complex flux pinning through an optimization of structural coupling between the GdBCO and the LSMO layers.

Controllable perovskite crystallization via potassium pretreatment toward high-performance solar cells

High-photoelectric performance and long-term stability of perovskite solar cells (PSCs) are closely related to the crystallinity and morphology of organic–inorganic halide perovskite films. However, interfaces and grain boundary defects of perovskite films could degrade the quality of perovskite films. In this work, potassium nitrate (KNO3) was taken to pretreat the compact TiO2 layer by a simple spin-coating method, which can simultaneously passivate both the electron transport layer (ETL)/perovskite interface defects and grain boundaries defects in perovskite films. Accordingly, the crystallinity and absorption intensity of the perovskite films were improved, which also enlarged the grain size, prolonged carrier lifetimes, and reduced the defect density. Therefore, an enhancement of short-circuit current density ranges from 22.56 to 24.00 mA cm−2 and a corresponding power conversion efficiency increases from 16.74% to 19.26%. PSCs also show that improved operational stability was 40%–65% with only 20% power conversion efficiency loss after 320 h under the relative humidity. The ETL modified by KNO3 reported herein provided a new approach of defect passivation with high-performance PSCs.

Highly enhanced field emission from vertically aligned carbon nanotubes grown on a patterned substrate via non-lithographic method

In the present work, a silicon substrate has been patterned with a gold thin film of thickness 15 nm using thermal evaporation , followed by growth of carbon nanotubes (CNTs) using thermal chemical vapor deposition . The effect of temperature on the growth of CNTs on Au patterned substrate is studied using Raman and Field emission scanning electron microscope (SEM). A significant change in the growth of the CNTs grown on Au film patterned substrate with temperature can be observed using SEM images. However, no significant change in the micro crystallinity of the films was observed. Field emission properties of vertically aligned carbon nanotubes, grown at different temperatures, on gold film patterned substrate has been investigated. For the non-patterned substrate, for the CNT film grown at 900 °C, the current density comes out to be 8.0 mA/cm 2 @ 4.8V/μm, which increases to 14.6 mA/cm 2 in the case of CNT film grown on gold patterned substrate. The observed enhancement of nearly 180% in current density for the patterned substrate as compared to non-patterned silicon substrate is primarily attributed to the reduced electric field screening. The reduced screening is realized with the help of COMSOL simulation, showing a significant enhancement in the local electric field near edges. • Use of novel non- Lithographic technique to pattern CNT films. • Effect of temperature on the Growth of vertically aligned CNTs on patterned substrate. • Nearly 180% enhancement in Field emission current density for CNTs grown over patterned substrate at 900 °C. • Simulation based verification of enhancement in the Field emission properties due to reduced screening.

FAPbBr3 perovskite quantum dots as a multifunctional luminescent-downshifting passivation layer for GaAs solar cells

Solar cells based on GaAs often include a wide-bandgap semiconductor as a window layer to improve surface passivation. Such devices often have poor photon-to-electron conversion efficiency at higher photon energies due to parasitic absorption. In this article, we deposit FAPbBr3 perovskite quantum dots on the AlInP window layer of a GaAs thin-film solar cell to improve the external quantum efficiency (EQE) across its entire absorption range, resulting in an 18% relative enhancement of the short-circuit current density. Luminescent downshifting from the quantum dots to the GaAs device contributes to a large effective enhancement of the internal quantum efficiency (IQE) at shorter wavelengths. Additionally, improved surface passivation of the window layer results in a 14–16% broadband increase of the IQE. These mechanisms combined with increased overall photon collection (antireflective effects) results in a doubling of the EQE in the ultraviolet region of the solar spectrum. Our results show a promising application of perovskite nanocrystals to improve the performance of well-established thin-film solar cell technologies.

Charge carrier dynamics and photovoltaic properties of near-infrared absorbing squaraine incorporated solution-processed additive-free PTB7:PCBM based ternary solar cells

The introduction of a third component vehemently modifies the morphology and charge carrier dynamics in the blend of a donor–acceptor pair, thereby affecting the photovoltaic properties of organic solar cells (OSCs). Combining steady-state, impedance, and transient spectroscopic measurements, photovoltaic properties of 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ) incorporated additive-free PTB7:PC70BM OSCs are assessed. As observed from steady-state measurements, concomitant enhancement in open-circuit voltage (VOC) and short-circuit current density (JSC) has caused a 33% enhancement in power conversion efficiency (PCE) with good reliability and reproducibility. On introducing 25 wt.% SQ to the OSCs, V OC has increased from 0.74 to 0.80 V, while J SC has improved from 11.3 to 13.9 mA cm−2 with an increment in exciton dissociation probability rate from 81.5% to 94.9%. However, the fill factor values show inconsistent marginal variations with SQ addition. Equivalent circuit modeling of bias-voltage dependent impedance spectra along with transient photovoltage measurements reveal an improvement in effective charge carrier lifetime for the SQ incorporated OSCs, in comparison to the binary device. The addition of SQ also ensures better charge transport and extraction, as evidenced by photo-CELIV and transient photocurrent analysis. Atomic force microscopy (AFM) images confirm the effective tuning of the morphology of the active layer when SQ is introduced into the binary blend, favoring efficient charge dissociation and transport. The possible operation mechanism of SQ incorporated ternary OSCs is proposed based on photoluminescence and AFM measurements. Moreover, the un-encapsulated OSC with 25 wt.% SQ has retained 91% of the initial PCE, while for the binary device the PCE declined to ∼75% of the initial value after 200 h of continuous 1 sun illumination from a white LED in ambient atmosphere.

Interlayer modification for high-performance and stable solid oxide electrolysis cell

Solid oxide electrolysis cells (SOECs) are an attractive technology that can convert energy into hydrogen or other syngas due to their high energy-conversion efficiency. To improve both performance and stability of SOECs, the effect of the interlayer modification between La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) air electrode and ytrria-stabilized zirconia (YSZ) electrolyte on the high-temperature water electrolysis performance was studied using electrochemical impedance spectroscopy at 1023 K under 40% H2O– 60% H2 fuel flow. Enhancement of the current density from 0.9 A/cm2 to 1.25 A/cm2 was achieved by replacing the porous Ce0.9Gd0.1O1.95 (GDC) interlayer by a dense GDC interlayer. Detailed analysis of the impedance spectra of the cell indicated that utilizing the dense GDC interlayer leads to a significant decrease of the ohmic resistance. Scanning electron microscopy-wavelength dispersive X-ray spectroscopy results show that the dense GDC interlayer could significantly reduce the secondary phase formation of SrZrO3 between the GDC and YSZ interface. Thus, the enhancement of the SOEC current density was also accompanied by good stability of the cell as confirmed over 50 h at 1023 K.

Multi-sub-inlets at cathode flow-field plate for current density homogenization and enhancement of PEM fuel cells in low relative humidity

Multi-sub-inlets are proposed at the cathode flow-field plate (FFP) of a polymer electrolyte membrane (PEM) fuel cell to improve the current density homogeneity and overall cell performance. The cathode main inlets andsub-inlets arefed with humidified and dry air, respectively, for appropriate membrane hydration and enhanced water removal to maintain thecathodetotalflow rateat the same relative humidity. The influences of the number of sub-inlets and the sub-inlet flow rate (the amount of air from the sub-inlets) on the overall cell performance with cathode reactant relative humidity (RHc) of 0%, 10%, and 20% are numerically investigated using a 3D multiphase fuel cell model. Compared with the conventional parallel FFP design, a multi-sub-inlet parallel FFP design can relieve oxygen maldistribution, improve water removal ability and dissolved water content, and maintain a low pressure drop, increasing the homogeneity of current density and overall cell performance. The numerical results also indicate that a reasonable increase in the sub-inlet flow rate for upstream sub-inlets can further benefit the maximum power density while maintaining the homogeneity of oxygen distribution. Multi-sub-inlet parallel FFP designs with RHc of 10% and 20% exhibit no significant differences in the distributions of internal physical quantities and cell performance, although 10% RHc saves water for air humidification.

Redox behaviour of CaCl2 melts in presence of moisture as impurity. Part I: Cyclic voltammetry

• Redox behaviour of bare CaCl 2 melts -explored using cyclic voltammetry at 900 °C at inert tungsten electrode. • Effect of addition of CaCl 2 .2H 2 O and Ca(OH) 2 in CaCl 2 melt studied using cyclic voltammetry. • Peak current densities observed in bare melts enhanced with addition of CaCl 2 .2H 2 O or Ca(OH) 2 . • Complex reduction behaviour attributed to formation of CaOHCl in melt at high temperatures. • Peak analysis of cyclic voltammograms and semi-integral curves carried out; cathodic reduction mechanism proposed. Redox behaviour of CaCl 2 melt at 900 °C is well known; what is not completely established so far is how the voltammetric behaviour of melt would be in presence of moisture. CaCl 2 prepared from vacuum drying of CaCl 2 .2H 2 O retained some residual moisture that eventually led to formation of CaOHCl at 900 °C as a result of which two redox couples were observed in the cyclic voltammograms at tungsten electrode. In order to decipher whether the redox peaks were a reflection of formation of single electro-active species, CaCl 2 .2H 2 O and Ca(OH) 2 were added in pre-electrolysed CaCl 2 melts and those were again analysed by cyclic voltammetry. Enhancement of peak current density of redox peaks, which were observed in pre-electrolysed CaCl 2 melt, was seen. This was attributed to the increased concentration of CaOHCl in the melt in presence of CaCl 2 .2H 2 O and Ca(OH) 2 . Subsequent to voltammetric peak analysis and logarithmic analysis of semi-integral curves for all melts, a mechanism involving formation of ( CaOH ) 2 2 + adsorbed undergoing a one-step two-electron transfer process in the first redox step was proposed. Second redox step resulted due to adsorption of O 2 - on tungsten, and its peak current density also got enhanced due to addition of CaCl 2 .2H 2 O and Ca(OH) 2 in melt.

Efficiency‐Enhanced Scalable Organic Photovoltaics Using Roll‐to‐Roll Nanoimprint Lithography

Light-trapping nanostructures have for decades been researched as a route to enhance the performance of organic solar cells (OSCs). Whereas the power conversion efficiencies (PCEs) of OSCs have reached above 18 %, industrially compatible devices made by scalable processing in air, using only nontoxic solvents and materials, have shown significantly lower performance values. Although light-trapping nanostructures may improve this, the methods for integrating the nanostructures are typically not compatible with industrial scale up. In this work, scalable, industrially compatible, nonfullerene-based OSCs are developed with integrated light-trapping nanostructures at the back electrodes in the devices. The OSCs are made by using scalable roll-to-roll (R2R) and sheet-to-sheet (S2S) processes and the nanostructures are made by using roll-to-plate (R2P) nanoimprint lithography. A fully scalable solution is thereby developed for industrially compatible nanostructured OSCs. The nanostructured devices show enhancements in PCE up to 25 % compared to reference cells, owing to an enhancement in the short-circuit current density (15 %) by enhanced absorption, and improved charge carrier extraction leading to an enhancement in the fill factor (7 %). Optical modeling is utilized to verify the optical effect of the nanostructures. The best devices attain a PCE of 6.5 %, which is the highest reported efficiency for air-processed slot-die coated ITO-free flexible PBDB-T : ITIC devices, here using nontoxic solvents.

Interpenetrating structure for efficient Sb2Se3 nanorod array solar cells loaded with CuInSe2 QDs sensitizer

The strong anisotropic electrical properties of one-dimensional (1D) nanostructure semiconductors, especially the anisotropic carrier transport, have a negative and significant influence on the performance of solar cells if the nanostructures have random orientation. Considering the advantages of nanorod solar cells in carrier transport, we have achieved growth of vertically aligned Sb2Se3 nanorod array with highly (hk1) orientation on CdS substrate, and constructed superstrate nanorod solar cells for the first time. The Sb2Se3 nanorod array solar cells exhibit the more efficient and long-range carrier transport in vertical direction. Furthermore, in order to suppress interface recombination, a CuInSe2 quantum dots (QDs) sensitizer has been applied to fill the volume between the nanorods completely, thus forming an interpenetrating nanocomposite structure. The CuInSe2 QDs can harvest additional light by absorption of visible light and contribute photocurrent. Meantime, the QDs function as a hole transport material and thus reduce the dependence of lateral transport. Consequently, the interpenetrating nanocomposite CuInSe2/Sb2Se3 solar cells display a power conversion efficiency of 7.54% with significant enhancements in the short-circuit current density and open-circuit voltage over pure Sb2Se3 nanorod cells. This is the highest efficiency for superstrate solar cells based on Sb2Se3 nanorod arrays.

Space charge limited current for bipolar flow in a crossed-field vacuum gap

In this paper, a numerical iteration approach is proposed to make an investigation of the influence of a transverse magnetic field on the space charge limited bipolar flow in a planar vacuum diode. By employing the method, the unknown limiting current density and potential distribution can be simultaneously determined. Considering a planar ion vacuum diode with a transverse magnetic field B parallel to the electrodes surface, we investigated the limiting current density as a function of B. Numerical calculations show that the limiting current density of the crossed-field vacuum diode may be approximately given by Je=JCL[a(B/BH)b+F], where JCL is the CL law and BH the Hull cutoff magnetic field, and a and b are the function of the ion current density, respectively. The physical meaning of F may be interpreted as the 1D current density enhancement factor due to the effect of ions for B=0. In the absence of ions, the limiting current solution is recovered in a crossed-field vacuum gap.

Pressure Dependence of Superconducting Properties, Pinning Mechanism, and Crystal Structure of the Fe0.99Mn0.01Se0.5Te0.5 Superconductor.

We have investigated the pressure (P) effect on structural (up to 10 GPa), transport [R(T): up to 10 GPa], and magnetic [(M(T): up to 1 GPa)] properties and analyzed the flux pinning mechanism of the Fe0.99Mn0.01Se0.5Te0.5 superconductor. The maximum superconducting transition temperature (Tc) of 22 K with the P coefficient of Tc dTc/dP = +2.6 K/GPa up to 3 GPa (dTc/dP = −3.6 K/GPa, 3 ≤ P ≥ 9 GPa) was evidenced from R(T) measurements. The high-pressure diffraction and density functional theory (DFT) calculations reveal structural phase transformation from tetragonal to hexagonal at 5.9 GPa, and a remarkable change in the unit cell volume is observed at ∼3 GPa where the Tc starts to decrease, which may be due to the reduction of charge carriers, as evidenced by a reduction in the density of states (DOS) close to the Fermi level. At higher pressures of 7.7 GPa ≤ P ≥ 10.2 GPa, a mixed phase (tetragonal + hexagonal phase) is observed, and the Tc completely vanishes at 9 GPa. A significant enhancement in the critical current density (JC) is observed due to the increase of pinning centers induced by external pressure. The field dependence of the critical current density under pressure shows a crossover from the δl pinning mechanism (at 0 GPa) to the δTc pinning mechanism (at 1.2 GPa). The field dependence of the pinning force at ambient condition and under pressure reveals the dense point pinning mechanism of Fe0.99Mn0.01Se0.5Te0.5. Moreover, both upper critical field (HC2) and JC are enhanced significantly by the application of an external P and change over to a high P phase (hexagonal ∼5.9 GPa) faster than a Fe0.99Ni0.01Se0.5Te0.5 (7.7 GPa) superconductor.

Optically photoactive Cu–In–S@ZnS core-shell quantum dots/biopolymer sensitized TiO2 nanostructures for sunlight energy harvesting

Colloidal semiconductor quantum dots (QDs) have been intensively investigated because of their remarkable tunable optical and electrical properties for potential clean energy production through solar photoconversion devices. Herein, we present for the first time the design and development of a hybrid nanostructure for applications in sunlight energy photoconversion, relying on a “safe and sustainable by design (SSD)” strategy, as follows: a) “Cadmium-free” (non-Cd-containing) inorganic semiconductor quantum dots (QDs), as optically active nanomaterials composed of quaternary Cu–In–S/ZnS systems (ZCIS); b) carboxylic-functionalized cellulose derivative (CMC) as biopolymer ligand and macromolecular stabilizing agent; c) A green chemistry approach based on an aqueous synthesis at mild conditions (e.g., pH, temperature, “organic-free”, nontoxic precursors) for creating water-soluble supramolecular colloidal core-shell nanostructures (i.e., [email protected], core: ZCIS; shell: CMC); d) As a proof-of-concept, the fabrication of a photoelectrochemical cell (PEC-cell) based on a solid-liquid heterojunction using the photoanode composed of TiO2 sensitized by [email protected] nanohybrids. Regarding optical properties, the results demonstrated that the [email protected] nanohybrids presented absorption/emission characteristics with maxima responses within the visible range of the light spectrum, which is prospectively appropriate for sunlight photoconversion applications. The solid-liquid junction photoelectrochemical cells (PEC-cell) fabricated using TiO2 films deposited onto ITO glass slides sensitized by ZCIS QDs evidenced photoactivity under visible light illumination using “dark” (“OFF”) and “light” (“ON”) cycles. Moreover, the PEC-cells confirmed the significant enhancement of photoinduced current density (over 150%) upon illumination when the relative sensitization density associated with the ZCIS QDs/TiO2 ratio was increased, and ethanol was used as the co-solvent. The results were credited to better contact between ZCIS QDs and TiO2 nanoparticles, tailoring a more favorable energy level alignment at the heterojunction interfaces, promoting the formation of a cascade of conduction band edges. Thus, these quantum dot-sensitized nanostructures developed through a sustainable and biocompatible approach produced strictly via green chemistry process can be anticipated as a sustainable alternative to the existing heavy metal-based sunlight photoactive optical nanomaterials after further optimization of conversion efficiency parameters.

Harvesting Sub-bandgap Photons via Upconversion for Perovskite Solar Cells.

Lanthanide-based upconversion (UC) allows harvesting sub-bandgap near-infrared photons in photovoltaics. In this work, we investigate UC in perovskite solar cells by implementing UC single crystal BaF2:Yb3+, Er3+ at the rear of the solar cell. Upon illumination with high-intensity sub-bandgap photons at 980 nm, the BaF2:Yb3+, Er3+ crystal emits upconverted photons in the spectral range between 520 and 700 nm. When tested under terrestrial sunlight representing one sun above the perovskite's bandgap and sub-bandgap illumination at 980 nm, upconverted photons contribute a 0.38 mA/cm2 enhancement in the short-circuit current density at lower intensity. The current enhancement scales non-linearly with the incident intensity of sub-bandgap illumination, and at higher intensity, 2.09 mA/cm2 enhancement in current was observed. Hence, our study shows that using a fluoride single crystal like BaF2:Yb3+, Er3+ for UC is a suitable method to extend the response of perovskite solar cells to near-infrared illumination at 980 nm with a subsequent enhancement in current for very high incident intensity.

Evolution of structural and optoelectronic properties in fluorine–aluminum co-doped zinc oxide (FAZO) thin films and their application in CZTSSe thin-film solar cells

The window layer is an important layer that transmits sunlight and generates electric current as the carriers move. Aluminum (Al) -doped zinc oxide (AZO) has been widely applied as the window layer in thin-film solar cells (TFSCs) owing to its favorable optoelectronic properties, as its properties can be controlled and further improved with suitable dopants. In this study, we strategically co-dope Al and fluorine (F) in ZnO thin films (FAZO) to improve the transmittance with controlled carrier concentration. To study the influence of F dopant on the structural, optical, and electrical properties of FAZO thin films, the F doping concentration is varied (0–1.5%) while keeping the Al content fixed (2%). With increasing F doping concentration, the carrier concentration, transmittance, and bandgap values increase, whereas, the sheet resistance and resistivity of the single-layer FAZO thin films decrease, compared to the reference AZO film. The addition of a small amount of F alters the surface roughness with increasing concentration. The properties of the single-layer FAZO thin films show deteriorated properties at the highest doping concentration (1.5%). Under the optimum condition of 1% F, FAZO thin films exhibit the lowest sheet resistance of 5.84 Ω/sq, in addition to the highest transmittance of 89.3% in the visible light region. Furthermore, the FAZO thin films applied in Cu2ZnSn(S,Se)4 (CZTSSe) device shows significant enhancements in the short-circuit current density (Jsc) and fill factor (FF), resulting in improved device performance from ~8 to 9.57%.

Three-Dimensional Modeling of Anode-Supported Planar SOFC with Corrugated Electrolyte

The aim of this work is to analyze the effect of corrugated electrolyte on the cell performance. The corrugated electrolyte is applied to the traditional anode-supported planar solid oxide fuel cell (SOFC) based on the theory of mesoscale electrode-electrolyte interface modification. Three-dimensional models of SOFCs with electrolytes with different corrugation heights and periods are developed. In order to better understand the influence mechanism of corrugated electrolyte, not only the effect of the corrugated electrolyte on the overall cell performance is analyzed, but also the local gas distribution, concentration polarization, activation polarization, exchange current density and electron current density are discussed. The results show that the corrugated electrolyte leads to a decrease in the local exchange current density, but the enlargement of the activation reaction zone leads to an increase in the total charge transfer, thereby resulting in an improvement in cell performance. The enhancement of average current density with an expansion factor of 2 has a maximum value of 56.9% at an operating voltage of 0.7 V.

Development of arsenic doped Cd(Se,Te) absorbers by MOCVD for thin film solar cells

Recent developments in CdTe solar cell technology have included the incorporation of ternary alloy Cd(Se,Te) in the devices. CdTe absorber band gap grading due to Se alloying contributes to current density enhancement and can result in device performance improvement. Here we report Cd(Se,Te) polycrystalline thin films grown by a chamberless inline atmospheric pressure metal organic chemical vapour deposition technique, with subsequent incorporation in CdTe solar cells. The compositional dependence of the crystal structure and optical properties of Cd(Se,Te) are examined. Selenium graded Cd(Se,Te)/CdTe absorber structure in devices are demonstrated using either a single CdSe layer or CdSe/Cd(Se,Te) bilayer (with or without As doping in the Cd(Se,Te) layer). Cross-sectional TEM/EDS, photoluminescence spectra and secondary ion mass spectroscopy analysis confirmed the formation of a graded Se profile toward the back contact with a diffusion length of ~1.5 μm and revealed back-diffusion of Group V (As) dopants from the CdTe layer into Cd(Se,Te) grains. Due to the strong Se/Te interdiffusion, CdSe in the Se bilayer configuration was unable to form an n-type emitter layer in processed devices. In situ As doping of the Cd(Se,Te) layer benefited the device junction quality with current density reaching 28.3 mA/cm 2 . The results provide useful insights for the optimisation of Cd(Se,Te)/CdTe solar cells. Compositional control of optical band gap in Cd(Se,Te) thin films (0 ≤ x ≤ 1) (left) and the Se profile in finished Cd(Se,Te) devices (right) fabricated by MOCVD. • Cd(Se,Te) thin films (0 ≤ x ≤ 1) deposited with linear compositional control using a chamber-less MOCVD process. • CdSe-only and CdSe/CdSe 0.2 Te 0.8 bilayers utilised for Cd(Se,Te) grading in devices. • In-situ and ex-situ group V (arsenic) doping of the graded Cd(Se,Te) obtained. • Device performance improved for thinner CdSe layers and in-situ doped bilayers. • Good control of Se profile achieved via CdSe and CdSe/CdSe 0.2 Te 0.8 properties.