Hydrogen Dilution Research Articles

Risk assessment of hydrogen leakage and explosion in a liquid hydrogen facility using computational analysis

In this study, the dispersion and explosion of liquid hydrogen (LH2) in leakage accidents are investigated using the Flame Accelerator Simulator (FLACS) code. The study focus was a liquid hydrogen research facility in Gimhae, South Korea. Simulations were conducted under various conditions by varying the mass flow rates (0.61 and 0.3 kg/s), directions (lateral in areas with minimal structures, lateral towards a tube trailer truck, and downward), and durations (90 and 180 s) of leakage. The results indicated that higher leakage mass flow rates produce a larger flammable cloud volume (FCV), resulting in higher maximum overpressures than that caused by lower flow rates. Downward leakage generally resulted in a larger FCV and higher overpressure than lateral leakage. The explosion characteristics were also influenced by geometry of LH2 facility, including the presence of structures in the leakage path. Contrastingly, leakage duration had a minimal effect on the maximum overpressure because an increased duration causes a greater dilution of hydrogen, only slightly expanding the FCV. According to the overpressure–impulse diagram, higher leakage flow rates cause severe health risks, approaching thresholds for lung rupture and 100% fatality. Contrary to the minor damages caused by lower leakage flow rates. High flow rates, particularly with downward leaks, can cause significant structural damage in brick buildings, potentially leading to partial demolition.

Investigation structural heterogeneities in hydrogenated nanocrystalline silicon thin films from argon-diluted silane dusty plasma PECVD

This study presents a novel approach for achieving a high deposition rate of nanocrystalline hydrogenated silicon (nc-Si:H) thin films using dusty plasma, eliminating the need for hydrogen dilution. Contrary to conventional beliefs, the research demonstrates that crystalline seeds can nucleate directly from the plasma environment itself. The investigation explores the relationship between plasma parameters and the degree of crystallinity in the deposited films, along with the characterization of structural inhomogeneities throughout the film's thickness. Raman spectroscopy, X-ray diffraction, and Transmission Electron Microscopy (TEM) are utilized for detailed analysis. The results reveal intriguing variations in crystallinity along the film's thickness, with higher crystallinity observed near the surface compared to regions closer to the substrate interface. In-depth analysis of grain size variation reveals that the average crystallite size decreases near the surface and increases in the bulk volume of the material. Additionally, deposition parameters, specifically power and pressure, are found to influence grain sizes, with higher values promoting larger grain growth. Notably, the observation of conical growth in layers deposited from dusty plasma presents a promising avenue for achieving controlled and desirable microstructures. This study sheds light on the critical influence of deposition parameters on film properties and the potential of dusty plasma for achieving desirable microstructures in nc-Si:H thin films. The findings offer valuable insights for tailoring thin film properties in diverse technological applications.

Heavy Boron-Doped Silicon Tunneling Inter-layer Enables Efficient Silicon Heterojunction Solar Cells.

P-type hydrogenated nanocrystalline silicon (nc-Si:H) has been used as a hole-selective layer for efficient n-type crystalline silicon heterojunction (SHJ) solar cells. However, the presence of an additional valence band offset at the interface between intrinsic amorphous hydrogenated silicon and p-type nc-Si:H films will limit the hole carrier transportation. In this work, it has been found that when a heavily boron-doped silicon oxide layer deposited with high hydrogen dilution to silane (pB) was inserted into their interface, the fill factor of SHJ solar cells increases 3% absolutely because of the reduced valence band offset and the increased opportunity to provide a hopping tunnel assisted by the doping energy level and valence band tail states. Furthermore, the additional boron incorporation in intrinsic amorphous silicon adjacent to pB helps to enhance the built-in electric field, thus increasing the hole selectivity. By these means, the power conversion efficiency was improved from 23.9% to approximately 25%.

On the role of hydrogen inhibition in gas-phase methane pyrolysis for carbon capture and hydrogen production in a tubular flow reactor

The thermal pyrolysis of methane enables economically competitive hydrogen production without direct CO2 emissions. Although several mechanisms for the process have already been proposed, especially the inhibitory effect of hydrogen as well as the process operation at increased pressure have not yet been fully clarified. In this context, the present work investigates the influence of hydrogen and argon as inert gas on product composition, methane conversion, and hydrogen selectivity as a function of temperature (1000 °C to 1600 °C), residence time (1 s to 7 s), molar dilution ratio (1:1–4:1), and pressure (1 bar to 4 bar) in a high-temperature reactor. Within the scope of this work, total differences in CH4 conversion of up to 50 % could be observed at equal process parameters between an argon and hydrogen dilution, underlining the potential impact of diluents on the overall process. Moreover, increasing the pressure from 1 bar to 4 bar reduces the formation of byproducts significantly for both H2 and Ar as diluent, however, with different mechanistic characteristics. The most remarkable difference is the formation of propylene that exclusively takes place in argon-diluted reaction gas mixtures. This occurrence persists unabated, even under elevated pressures and temperatures reaching as high as 1600 °C. We ascribe this phenomenon to the interaction of methyl and ethyl radicals, establishing it as an impasse to further reactions leading to the formation of solid products. Herewith, the study provides novel insights from a reaction engineering perspective as well as from a process development perspective and clarifies the role of the dilution gases hydrogen and argon on the methane pyrolysis reaction.

Accelerating flammable gas cloud dissipation in hydrogen leakage during refilling hydrogen-powered vehicles via employing canopy fans

Mitigating the hydrogen leakage risk during the refilling process contributes to promoting the hydrogen energy commercialization. In this study, the high-pressure hydrogen leakage and dilution characteristics were analyzed with fans installed on the hydrogen refueling station canopy. Two fan conditions are involved: blowing upwards condition, and blowing downwards condition. The role of leakage pressure, atmospheric wind velocity, and fan conditions on the spatiotemporal evolutionary characteristics of flammable gas clouds (FGC) were discussed. Results showed that the hydrogen distribution is significantly impacted by wind velocity and fan blowing conditions when the hydrogen-powered vehicle is refueled. At a small leakage pressure, under windless conditions, employing fans contribute to the FGC dissipation. At windy conditions the fan blowing upwards does not accelerate the FGC dissipation, but rather increases the its volume and slows down its dilution. At a large leakage pressure, at small wind velocities, fan blowing upwards contributes to FGC dilution. However, at large wind velocities, fan blowing upwards is not effective in accelerating the hydrogen dilution. In all the scenarios, fan blowing downwards always helps to accelerate the hydrogen dilution. This study offers a pragmatic approach to effectively mitigate the risk of hydrogen leakage during the refilling process.

Study on P-a-Si:H properties of N-type heterogeneous junction solar cells manufactured by large-area parallel plate PECVD machine

P-type hydrogenated amorphous silicon (P-a-Si:H) plays an important role in heterojunction solar cells. On the one hand, P-a-Si:H processed by plasma enhanced vapor deposition (PECVD) can selectively collect carrier holes on the rear of N-type silicon based heterojunctions with intrinsic thin layer (HJT) solar cells (in this article, the back ride of the cell is P-a-Si:H); On the other hand, the ohmic contact between P-a-Si:H and conductive ITO film is beneficial for hole transport. Therefore, the performance of P-a-Si:H has very significant impact on the property of HJT solar cells. The electrical conductivity, impurity activation energy, and passivation performance of silicon wafer surface are the core performance indicators of P-a-Si:H materials themselves. In this paper, we systematically research the optimal RF power density, doping concentration (diborane doped), hydrogen dilution ratio and plate spacing for the growth process of P-a-Si:H using a self-developed large-area parallel plate PECVD equipment (Jincheng Machine). The results show that the P-a-Si:H has an electrical conductivity of 1.27 × 10−3 S/cm and an activation energy of 251 meV, and the maximum mass production efficiency of the HJT solar cell is 25.21%, Voc is 741 mV and Jsc is 41.57 mA/cm2.

Hydrogenated silicene grown by plasma enhanced chemical-vapor deposition

Silicene, a 2D hexagonal structure of silicon, has shown great promise for next-generation advanced electronic devices due to recent progress. However, one major obstacle to its application and integration into devices is its strong tendency of rapid oxidation in an ambient environment. Enhancing the chemical inertness by means of chemical modification without comprising its unique structure and properties is vital. Here, we report the fabrication of hydrogenated silicene grown on polycrystalline Ag films by means of plasma-enhanced chemical-vapor deposition (PECVD) with proper hydrogen dilution. Our Raman spectroscopy and x-ray diffraction results show the existence of typical monolayer and few-layer silicene. The x-ray photoelectron spectroscopy demonstrates its oxidation resistance after a few minutes of air exposure in a class 100 clean room. We propose that PECVD silicene can be an alternative to molecular-beam-epitaxy silicene for potential low-cost and large-area silicene applications.

Impact of Pressure and Hydrogen Dilution on the Kinetics of Methane Decomposition in AC-Excited, High Pressure Plasmas

Impact of Pressure and Hydrogen Dilution on the Kinetics of Methane Decomposition in AC-Excited, High Pressure Plasmas

Improving the air supply and hydrogen dilution control of a fuel cell electric vehicle with explicit model predictive control

This study demonstrates the applicability of an explicit model predictive controller (ExMPC) to the air mass flow control in a fuel cell electric vehicle. The two control tasks comprise the supply of air to the fuel cell stack for the electrochemical reaction as well as the dilution of hydrogen in the outlet gas flow of the cathode subsystem. With the aim of achieving zero control deviation for steady states, the linear model in the state observer is extended with two perturbations. During the experimental validation of the proposed controller, fast dynamics are achieved with the ExMPC, which generally exploits the limits of the control variables. After the calibration of the ExMPC, the final comparison to a set of reference PI controllers reveals a significant improvement in the closed-loop behavior of the cathode subsystem during step changes in the controller setpoints.

Tritium transport in the vacuum vessel pressure suppression system for helium cooled pebble bed

In the frame of the safety studies for the EU-DEMO reactor, attention is paid to the hydrogen concentration in the vacuum vessel and connected volumes since it would lead to a possible hazard of releasing tritium and activated dust. The risk of explosion cannot be excluded a priori if H2 stockpiles. For this reason, in both water (WCLL) and helium (HCPB) cooled breeding blanket concepts of EU-DEMO, the problem is under investigation with a cross-reference between the available technologies in fission (such as the Passive Autocatalytic Recombiners – PAR) and fusion application. In particular, the recent analyses pointed out the implementation of the PARs into the Vacuum Vessel Pressure Suppression System or linked systems.This paper evaluates the Hydrogen behavior (main mobilized tritium source term) for the Helium-Cooled Pebble Bed (HCPB) VVPSS concept. The analyses preliminary investigate the stratification of the hydrogen mass inventory inside the PSS. In particular, a MELCOR 1.8.6 model of the PSS, based on past activities aimed at dust transport and thermohydraulic analyses, is adopted. The paper also introduces the applicability of PAR technology in the operation range of fusion devices, analyzing the problem of the recombination rate due to the dilution of Hydrogen after a Helium blowdown.

Material Properties of Nanocrystalline Silicon Carbide for Transparent Passivating Contact Solar Cells

Due to its high transparency, silicon carbide can replace amorphous silicon as a front contact material in crystalline silicon solar cells. Herein, first a look at doping in nc‐SiC:H with different deposition techniques is taken. Then, the influence of various deposition conditions for hot wire chemical vapor deposition‐prepared nc‐SiC:H is investigated. Both the electrical conductivity and the optical bandgap increase simultaneously for a multitude of deposition parameters. Combining a high filament temperature of the catalytic filament, a high hydrogen dilution of the precursor gas and an overall low total gas flow, conductivities of 0.38 S cm−1 in combination with an optical bandgap of 3.2 eV can be achieved. In the last section, a closer look into the dependencies of the layer thicknesses of the two different nc‐SiC:H layers applied in solar cells on the cell performance is taken. While the layer with conducting properties only has minor influences on cell properties, a trade‐off between passivation and fill factor is identified for the passivating nc‐SiC:H layer. For thicker layers, the passivating nc‐SiC:H layer achieves a very high implied open‐circuit voltage above 740 mV, but the fill factor starts to degrade due to a very low conductance of the layer.

Growth, structural and vibrational properties of hydrogenated nanocrystalline silicon thin films prepared by radiofrequency magnetron sputtering technique at room temperature

The main objective of this paper is to produce the hydrogen-free and hydrogenated nanocrystalline silicon (nc-Si:H(x)) thin films deposited onto the single-crystalline Si(100) wafer by radio-frequency magnetron sputtering (RF-MS) at a substrate temperature of ∼ 300 K. Sputtering was effectuated by a microwave plasma in a mixture of argon and hydrogen (Ar + (H2(x)) gasses taken at different proportions of hydrogen dilution: x = 0, 2.5, and 5 sccm (standard cubic centimeter per minute). The deposition rates of the nc-Si:H were fully controlled, and the thickness of these films was ∼ 200 and 300 Å. Pt-capping layer was deposited in order to protect the nc-Si:H layer from oxidation. The thickness of the capping layer was fixed at ∼ 5 Å.The effects of the hydrogen flow rate and post-growth thermal treatment on the crystalline structure and morphology of as-grown nanocrystalline silicon thin films were systematically investigated by ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS), atomic force microscopy (AFM), grazing incidence x-ray diffraction (GI-XRD) and micro-Raman spectroscopy methods. From the measured data, the average nanocrystallite sizes, surface morphology and other important characteristics of these thin films were analyzed. The grown nc-Si:H thin films may be used as a semiconducting electrode material for electrochemical proton production, which is of great technological importance, especially for solid-state electrochromic device applications.

Explosion-prevention strategies of airflow controlling and closed-inerting for hydrogen dilution in utility tunnel

Under the large-scale application of hydrogen energy and the acceleration of utility tunnel construction in China, the hydrogen pipeline would enter the utility tunnel soon. The explosion-prevention strategy is of important to hydrogen transportation in utility tunnel. Thus, a series of comparative studies were carried out in the present study, to explore the high efficiency dilution methods for unexpected hydrogen leak scenarios. (1) Effects of source type and domain extension were further validated based on our previous numerical model. The small-hole model was found to be simple and feasible for pipe release simulation, and has the same high accuracy like the notional nozzle model. The influence of unexpanded domain is acceptable. (2) Investigation of the explosion-prevention strategies was performed based on the finding of the worst leakage case, and hydrogen leaks at the middle of the upwind tunnel with upward leak direction was found to be the worst leakage case for the normal utility tunnel. (3) Compared with the layouts of lateral vents and the single horizontal air distributor, the middle exhaust vent was found to be the optimal airflow controlling strategy. (4) Furtherly, compared to the optimal airflow controlling strategy, closed-inerting was validated to be the most efficient dilution method. In the closed-inerting cases, the peak value of the flammable gas volume which is only ∼40% of the unimproved case appears. After that, the flammable cloud volume decays gradually, while the value increases steadily in the initial unimproved case. No obvious difference was found between the N2 and CO2 injection cases.

Utilisation of Ammonium Carbonate in a Solid Oxide Cell

In this work, the utilisation of aqueous ammonium carbonate, (NH4)2CO3, has been investigated as a fuel for solid oxide cell technology for the first time. In its pure form, ammonium carbonate is a solid white power that can easily be stored. It is easily dissolved in water to create an ammonium-rich aqueous solution and can therefore potentially be utilised as a fuel for solid oxide cell technology 1. Aqueous ammonium carbonate is produced as a waste stream from the coke production processes required for steelmaking. Coke is needed as a fuel for blast furnaces and is typically produced via dry distillation of coal in the absence of oxygen, which yields a waste gas stream known as coke oven gas (COG). Cleaning and treatment of COG yields an aqueous waste stream containing ammonia (28 wt%), water (61 wt%), phenol-based tars (5 wt%), carbon dioxide (3.9 wt%), hydrogen sulfide (0.6 wt%) and trace levels of hydrogen cyanide and sodium hydroxide. Due to the presence of carbon dioxide, a significant fraction of the ammonia is present in the form of ammonium carbonate. Significant amounts of COG are produced due to steelmaking, with 44,000 Nm3 produced every hour at the Tata Steel Port Talbot (UK) site alone, corresponding to 264 kg of ammonia every hour 2. Presently, ammonia waste is disposed via incineration, wasting energy and a valuable resource, and contributing to air pollution and greenhouse gas emissions.Ammonia is a well-established chemical commodity used mainly for the manufacture of mineral fertiliser 3. Recently, ammonia has gained more interest in the energy sector since it is a carbon-free hydrogen carrier and can be used directly and efficiently in fuel cells and gas turbines without emitting CO2 4. It also has a high energy density (12.7 MJ L-1) and its storage as a liquid requires less energy-intensive conditions (-33 ˚C) in comparison with hydrogen (-253 ˚C) 5. The high volumetric hydrogen density of ammonia (17.8 wt%) and ease of liquefication make it ideal for capturing, storing, and transporting hydrogen.This work investigates the utilisation of aqueous ammonium carbonate solutions in a solid oxide cell. The electrical performance and gaseous outputs of an anode-supported solid oxide cell operating in fuel cell and electrolysis mode at 750 °C have been established. The cell performance was characterised by current-voltage (I-V) curves and the dried gaseous outputs were characterised by online quadrupole mass spectrometry (QMS).QMS measurements showed that upon delivery to the anode, ammonium carbonate decomposed to form gaseous hydrogen, carbon dioxide and nitrogen, with no NO x emissions detected. No carbon monoxide was detected due to the presence of the water-gas shift reaction. In fuel cell mode, QMS measurements showed the cell utilised hydrogen to produce electrical power. The I-V curves (see Figure) showed the electrical power output was lower than pure hydrogen, due to greater open circuit voltage and concentration losses caused by dilution of hydrogen in the steam, carbon dioxide and nitrogen present. The activation losses observed under aqueous ammonium carbonate were very low.In electrolysis mode, the cell utilised steam to produce hydrogen, which was diluted in carbon dioxide and nitrogen. At 1.4 V, QMS measurements showed the output gases were composed of 60 vol% hydrogen, 29 vol% nitrogen and 11 vol% carbon dioxide. No co-electrolysis of carbon dioxide was observed, and no carbon monoxide was produced. The main losses under ammonium carbonate were ohmic overpotentials (see Figure), with no activation or concentration losses observed. Whilst this work has focussed on the short-term performance and outputs of the cell, no potential causes of long-term deactivation were identified. M. Ragu, C. J. Laycock, G. Owen, G. Lloyd, and A. Guwy, ECS Trans., 103 (1), 2173-2184 (2021). doi.org/10.1149/10301.2173ecstS. C. J. Van Acht, C. J. Laycock, S. J. W. Carr, J. Maddy, A. J. Guwy, G. Lloyd, and L. F. J. M. Raymakers, Int. J. Hydrogen Energy, 45, 15196-15212 (2020) doi.org/10.1016/j.ijhydene.2020.03.211.M. A. de Graaff, N. Hornslein, H. L. Throop, P. Kardol, and L. T. A. van Diepen, Adv. Agron., 155, 1-44 (2019). doi.org/10.1016/bs.agron.2019.01.001A. Valera-Medina, H. Xiao, M. Owen-Jones, W. I. F. David, and P. J. Bowen, Prog. Energy Combust. Sci., 69, 63–102 (2018). doi.org/10.1016/j.pecs.2018.07.001.M. Cheliotis, E. Boulougouris, N. L. Trivyza, G. Theotokatos, G. Livanos, G. Mantalos, A. Stubos, E. Stamatakis, and A. Venetsanos, Energies, 14(11), 3023-3042 (2021). doi.org/10.3390/en14113023 Figure. I-V and power curves of an anode-supported solid oxide cell operating on mixtures of hydrogen and aqueous ammonium carbonate at 750 °C. The mixtures indicated are balanced in pure hydrogen. Figure 1

Pilot impact on turbulent premixed methane/air and hydrogen-enriched methane/air flames in a laboratory-scale gas turbine model combustor

The impact of pilot flame operation on the combustion of pure methane and hydrogen-enriched methane (H2/CH4: 50/50 in vol%) fuels was investigated in a gas turbine model combustor under atmospheric conditions. The burner assembly was designed to mimic the geometry of an industrial burner, the Siemens DLE Burner, in which a concentric annular ring equipped with pilot flame burners is implemented in the dome of the combustor. Two pilot burner configurations have been investigated: a non-premixed and a partially premixed pilot arrangement. The performance of the pilot burners was evaluated for varying Reynolds number (Re) and H2 enrichment. High-speed OH∗ chemiluminescence imaging, as well as simultaneous planar laser-induced fluorescence measurements of the OH radicals and formaldehyde (CH2O) were used for evaluating the dynamics and structures of the flames for different conditions. Furthermore, emission measurements were carried out to determine the influence of hydrogen dilution on the NOx and CO emission levels. The main findings are (a) the effect of the pilot flame is sensitive to the Reynolds number of the main flame and the type of the pilot flame, (b) the stability range becomes narrower with increasing hydrogen ratio, due to the tendency to flashback, (c) non-premixed pilot flames lower the NOx and increase the CO emissions, albeit rather small differences in the emissions have been detected, and (d) the NOx and CO emissions become significantly lower with increasing hydrogen ratio.

Modeling the diffusion of flammable hydrogen cloud under different liquid hydrogen leakage conditions in a hydrogen refueling station

Constructing hydrogen refueling stations will be popular for hydrogen energy use in the future, and investigating the diffusion characteristics of hydrogen in a leakage incident is quite significant. The instantaneous evolution of flammable hydrogen clouds arising from liquid hydrogen leakage in a hydrogen refueling station is predicted using Ansys Fluent, and parametric analyses are conducted to reveal the effects of storage pressure, source height, and leakage direction on the distributions of the flammable regions. In addition, the feasibilities of heating the ceiling or the ground of the station after the leakage of liquid hydrogen to accelerate the hydrogen dilution are examined. The results show that the flammable region is stabilized at 90 s, the corresponding flammable hydrogen cloud volume is about 333 m3, and the extensions of downwind and vertical directions reach 10 m and 9.3 m. Storage pressure has a finite effect on the downwind diffusion distance of the flammable cloud. A lower source height tends to format the high-concentration hydrogen cloud near the ground while a higher source height helps separate the flammable clouds from the ground. The upward leakage direction leads to the maximum downwind diffusion distance of about 10.2 m while the downward leakage direction makes the high hydrogen concentration region confined below the ceiling. Just maintaining the ceiling at the initial temperature of 300 K is effective for accelerating the hydrogen dilution in the upward leakage. The maximum hydrogen concentration and the flammable volume can be reduced at rates of 0.35 vol % and 8% for every 50 K increase in heating temperature. For the downward leakage, keeping the ground at the initial temperature just works for the first 40 s in reducing the maximum hydrogen concentration, while increasing the heating temperature receives a gradually declined effect on reducing the flammable volume.

Pulsating one-dimensional detonation in ammonia-hydrogen–air mixtures

In this study, one-dimensional detonations in ammonia/hydrogen-air mixtures are numerically investigated by solving the fully compressible Navier-Stokes equations with detailed chemistry. Pulsating instabilities with single-mode are observed during the detonation wave propagation, accompanied by periodic coupling and decoupling of the lead shock wave and the reactive front. The ratio between driver pressure and initial pressure determines the overdrive degree and thus the oscillatory mode of detonation for a premixture with certain composition. The effects of hydrogen dilution and mixture equivalence ratio on pulsating detonations are also examined under a constant driver pressure. The growing hydrogen fraction in fuel blends significantly increases the oscillation frequency. In addition, the pulsating detonation frequency rises with increasing equivalence ratio under fuel-lean conditions, peaks under stoichiometric conditions, and falls under fuel-rich conditions as the equivalence ratio increases further. Evolutions of reactants, main intermediate radicals, and products are analysed in both fuel-lean and fuel-rich conditions. A chemical explosive mode analysis further confirms the highly-autoignitive nature of the mixture in the induction zone between reaction front and shock front where thermal diffusion plays a negligible role.

Spatially resolved electrochemical performance and temperature distribution of a segmented solid oxide fuel cell under various hydrogen dilution ratios and electrical loadings

Inhomogeneous distributions are essential factors resulting in degradations of performance and durability of a solid oxide fuel cell (SOFC). In this work, effects of hydrogen dilution ratio and electrical loading on spatially distributed electrical performance and temperature of a segmented SOFC are investigated. Interpretations of local electrode processes and polarization resistances including ion transport, charge transfer, and gas diffusion during potentiostatic operation of the whole cell are obtained. The segment near the gas outlet has the worst initial performance owing to considerably large oxygen surface exchange and reaction overpotential. The temperature distribution obtained by spline interpolation of the experimental data demonstrates that diluting the fuel significantly decreases the average cell temperature at open circuit voltage, which indicates the parasitic combustion heat cannot be ignored. Strongly inhomogeneous distributions of current density and temperature in the cell are observed at low hydrogen ratio and operating voltage, which leads to locally harsh conditions near the gas outlet region. Furthermore, microstructure analysis reveals that the cathode segment adjacent to the gas outlet undergoes greater degradation resulting from oxygen depletion of the cell under low voltage. The results facilitate better understanding of the inhomogeneous electrochemical and temperature behaviors in different zones of a SOFC.

Hydrogen effect on structural and optical properties of in-situ fabricated nc-Si:H prepared by facing targets sputtering

We report high-quality hydrogenated nanocrystalline silicon (nc-Si:H) thin films were prepared by facing targets sputtering (FTS) in the environment of Ar and H2 mixture gases. By increasing hydrogen dilution (RH) of FTS deposition, the structural evolution of as-fabricated Si-based films was observed. Fourier infrared spectroscopy (FTIR) shows that decrease in bonded hydrogen (CH) concentration, especially that of (Si-H2)n with increasing RH, indicating that the H etching effect increased atomic density of these films, thus improving film quality. With the RH increased, the Raman spectra show that the morphological transition from amorphous to crystalline states. We further reveal correlations between the degree of structural order in the amorphous network and the RH by calculating experimental data from the Raman measurements. Moreover, as-fabricated nc-Si:H films show large bandgap and narrow band tail states with increasing RH, which allows potential applications in the window passivation layer for HIT solar cells and Si-based charge-coupled devices (CCD). This work offers a novel route to fabricate high-quality nc-Si:H films for optoelectronic applications.

Improved interface passivation by optimizing a polysilicon film under different hydrogen dilution in N-type TOPCon silicon solar cells.

The passivation properties of a polysilicon (poly-Si) thin film are the key for improving the photovoltaic performance of TOPCon silicon solar cells. In this work, we investigate the influence of the poly-Si microstructure on the interface passivation and photovoltaic performance in TOPCon solar cells. The poly-Si thin films are prepared from phosphorus-doped hydrogenated microcrystalline silicon (μc-Si:H) layers deposited via plasma enhanced chemical vapor deposition (PECVD) under different hydrogen dilutions and recrystallized by high temperature post-deposition annealing. The results revealed that, as the hydrogen dilution ratio increases, the microstructure of the pre-deposited films transforms from an amorphous phase to a microcrystalline phase. Meanwhile, the effective minority carrier lifetime of the symmetrically passivated contact structure shows a maximum value of 1.75 ms, implying that the efficient passivation at the c-Si interface is obtained which is mainly attributed to the joint enhancement of the improved field effect passivation from poly-Si films and the reduced defects density on the silicon surface. Consequently, the devices displayed excellent rectification behavior with a rectifying ratio of 3 × 105, ascribed to the enhanced carrier transport with the high quality poly-Si film pre-deposited in the initial region of structural transition. Correspondingly, the obvious improvement of TOPCon solar cell performance was achieved, exhibiting an optimized conversion efficiency of 17.91%. The results provide an optimal design scheme for enhancing the photovoltaic properties of the TOPCon silicon solar cells.