Acceptor Dopant Concentration Research Articles

Investigating the potential of WO3 and WS2 as Cd-free buffer layers in Sb2Se3-Based thin-film solar cells: A numerical study with SCAPS-1D software

In this numerical study, the performance of thin-film solar cells (TFSCs) based on Sb2Se3 with WO3 and WS2 materials as Cd-free buffer layers was investigated using SCAPS-1D software. WO3 and WS2 were chosen for their suitable band gaps, good electrical conductivity, and optical transparency. The proposed solar cell structures, Au/Sb2Se3/WO3/ITO and Au/Sb2Se3/WS2/ITO were theoretically examined, considering various factors such as conduction band offset, absorber and buffer layer thickness, doping concentrations, series and shunt resistances, temperature, activation energy, and C–V characteristic. The conduction band offset at the absorber/buffer interface showed spike-like configurations, with values of 0.38 eV and 0.23 eV for the WO3 and WS2 buffer layers, respectively. The optimized thickness for the absorber layer in both structures was 1 μm, while for WO3 and WS2 buffer layers, it was 0.1 μm and 0.05 μm, respectively. The optimized acceptor and donor doping concentrations were 1 × 1016 cm−3 and 1 × 1018 cm−3, respectively. The efficiency of the proposed photovoltaic devices was found to be 9.538 % (with Voc = 0.561 V, Jsc = 30.856 mA/cm2, FF = 55.84 %) and 10.151 % (with Voc = 0.558 V, Jsc = 29.189 mA/cm2, FF = 62.34 %) for structures with WO3 and WS2 buffer layers, respectively. These results suggest that using non-toxic materials like WO3 and WS2 as buffer layers can be an efficient and environmentally friendly alternative to toxic CdS for fabricating cost-effective and highly efficient Sb2Se3-based TFSCs.

Co-doping effect on the microstructural and electrical properties of barium stannate materials

Proton-conducting perovskite oxides are of considerable interest to researchers as promising electrolytes for low- and intermediate solid oxide electrochemical cells. Therefore, designing new potential proton-conducting phases and improving the functional properties of known materials are of great importance from both fundamental and applied viewpoints. In the present work, BaSnO3 was selected as a reference proton-conducting system and then a co-doping strategy was employed to analyze ‘composition – structure – microstructure – transport properties’ relationships. To perform such an analysis, the properties of previously studied BaSn0.7M0.3O3–δ (M = In, Sc, Y) compounds were compared here to their co-doped derivatives, BaSn0.7In0.15Sc0.15O3–δ, BaSn0.7Y0.15Sc0.15O3–δ, and BaSn0.7In0.15Y0.15O3–δ. It is found that the type of dopant affects the materials sinterability, when more coarse-crystalline ceramics are formed with increasing the average ionic radii at the Sn-position. The introduction of Y3+-cations reduces both ionic and hole conductivities compared to single-doped with In3+ or Sc3+ barium stannate materials. However, simultaneous doping with In3+/Sc3+ cations minimizes the contribution of hole conductivity compared to that of Sc-doped barium stannate with the same acceptor dopant concentration.

Competition between built-in polarization and p–n junction field in III-nitride heterostructures

The high built-in polarization field is a fingerprint of III-nitride heterostructures. Alloy composition and doping profile significantly affect the magnitude of the electric field present in subsequent layers, but the sign of the electric field is usually defined by substrate polarity and external bias. Here, we propose to utilize acceptor and donor doping concentrations exceeding 1020 cm−3 to obtain a high junction field that can solely abolish built-in polarization for a polar (0001) InGaN/GaN quantum well (QW). We have used photoluminescence (PL), time-resolved PL (TRPL), and contactless electroreflectance in order to gain insight into the strength of the electric field present in the grown heterostructures. Good match between expected and measured electric field values was obtained. A dramatic decrease in the luminescence lifetime for a flat QW was confirmed using TRPL. The presented results open a way to realize devices that profit from the low built-in field, like photodetectors, using abundant polar substrates.

Degradation and Failure Mechanism of p-GaN Gate E-Mode GaN HEMTs

GaN-based power transistors are becoming pivotal devices for high power and high voltage operation due to their higher breakdown voltage, higher carrier mobility because of two-dimensional electron gas (2-DEG), better thermal resistance, higher frequency switching, and lower on-state resistance (RON) [1]. P-GaN gate E-mode GaN HEMTs have emerged as a center of extensive research to understand their operation and reliability [2]. However, one of the reasons the E-mode GaN HEMTs are not yet successfully utilized to their maximum potential is the lack of complete understanding of gate breakdown. Gate degradation of p-GaN gate E-mode GaN HEMT is less understood because of the complexities involving the operating conditions and variables such as gate length, the acceptor doping concentration in the p-GaN layer [3], p-GaN gate thickness, and design of the device [4-5]. To outline a consistent degradation mechanism, this work aims to present an electro-physical model of gate breakdown in p-GaN gate E-mode HEMTs.Lateral E-mode GaN HEMT devices with p-GaN gate configuration are used for this study. According to the Scanning Transmission Electron Microscopy (STEM) imaging of a new device, the AlGaN barrier is 10 nm thick, and the p-GaN cap is 65 nm. The gate-source and gate-drain lengths are 0.5 micrometer and 2.5 micrometer, respectively. The gate length defined by the p-GaN layer is 0.5 micrometer and the edges of the gate metal are pulled in from the top edge of the p-GaN layer by 40 nm. A 0.7 micrometer-long, source-connected field plate is over the p-GaN gate. The p-GaN gate is subjected to static stress to induce accelerated breakdown. Devices were stressed with HP 4155 Semiconductor Analyzer. The electrical measurements were performed with the source, drain, and substrate connected to the ground. FEI 200 Nova was used for Scanning Electron Microscopy (SEM) imaging and Focused Ion-Beam (FIB) milling. ARM JEM-200F with a Cs corrector was used for STEM.Our results show that time-to-fail is highly dependent on device operating conditions. We found no correlation between time-to-fail and initial gate current (IG0). Instead, a higher impact of temperature was found on the gate current of the device (IG) and time-to-fail at 100 °C. Gate failure at constant voltage stress was a single-stage failure. Under constant current stress, on the other hand, the gate shows a multi-stage failure. The breakdown mechanism depends on the impact of static stress on the gate degradation, starting with increased gate current leading to Schottky barrier leakage and finally to catastrophic contact failure. Our study shows that the metal/p-GaN interface at the gate finger becomes the weakest part of the gate stack, likely to be the initiation point of degradation. Metal/p-GaN interface and surface defects develop as percolation paths acting as leakage sources, and nano-cracks have been observed in the gate cap. FA also shows physical degradation at the metal/p-GaN cap due to electrical stress. Observed physical damage in the gate region is correlated to the gate leakage characteristics to develop an electro-physical failure model for gate breakdown in p-GaN gate E-mode GaN HEMTs.

Nitrogen-doped titanium dioxide as a novel eco-friendly hole transport layer in lead-free CsSnI3 based perovskite solar cells

After an abrupt rise in the efficiency of perovskite solar cells (PSCs), hole transport layer (HTL) as an essential factor for fabricating efficient PSC devices attract attentions. The pristine spiro-OMeTADspiro-OMeTAD, as most widely used HTL, still suffers from poor electrical conductivity, low hole mobility, and low oxidation rate. In this research, the spiro-OMeTAD is replaced by nitrogen doped TiO2 (N-TiO2) HTL. Then, the variation in the device design key parameters such as the thickness and bulk defect density of perovskite layer, simultaneous modifications of defect density and defect energy level, and acceptor doping concentration in absorber layer, and operating temperature are examined with their impact on the photovoltaic characteristic parameters. The standard lead-free CsSnI3–based PSCs with spiro-OMeTAD HTL is simulated using SCAPS-1D software. The CsSnI3-based solar cell with N-TiO2 as HTL showed higher efficiency of 27.03 % than the standard device with PCE of 23.63 % for conventional spiro-OMeTAD HTL.

Simulation and numerical modeling of high‐efficiency CZTS solar cells with a BSF layer

AbstractThe present paper deals with the photovoltaic performance‐based numerical evaluation of copper–zinc–tin–sulfur (CZTS) solar cells embedded with CZTSe as a back surface field (BSF) layer. CZTS has been considered a leading candidate for the fabrication of solar devices owing to its availability and absence of toxicity. Adding a BSF layer to a solar device is a novel way to boost efficiency. It reduces the recombination of the carriers at the back surface, thus increasing the overall current output of the solar cells. SCAPS 1D simulator is used to study the impact of several parameters on electrical properties like temperature, the thickness of the CZTS layer, acceptor doping concentration, and the impact of series and shunt resistances. Considering the optimized parameters in each layer of the solar cells, this work delivers 24.7% efficiency with the BSF layer, which is 8% more than that without the BSF layer. The results of this modeling will facilitate researchers to fabricate a highly efficient CZTS solar cell.

Device modelling and optimization of various n-i-p configurations for MASnI3 perovskite solar cells to achieve high efficiency using Solar Cell Capacitance Simulator-1D

Perovskite materials are potential light harvesters, and in specific tin-based absorbers such as methyl ammonium tin iodide (MASnI3) are non-toxic with distinguished optoelectronic properties. This is the first simulation report to explore the application of strontium titanate (SrTiO3) as an electron transport layer (ETL) in planar n-i-p MASnI3 perovskite solar cell (PSC) device. In an attempt to enhance the output performance of MASnI3 PSCs, a systematic approach is devised to determine appropriate alternative charge-selective materials via solar cell capacitance simulator (SCAPS-1D) software. The significance of varying thickness, donor doping concentration, acceptor doping concentration, defect density, diffusion length, and energy band offset for the reference PSC configuration TiO2/MASnI3/Spiro-OMeTAD are investigated. The optimized reference structure delivered 19.72% efficiency. In pursuit of high photovoltaic performance, seven different electron transport materials were comparatively examined. As a result, PCBM, In2S3, and CeO2 were considered not suitable due to their limited electrical performance. Consequently, seven inorganic hole transport layers (HTL) along with four suitable ETL were utilized in MASnI3 PSC to construct twenty-eight novel n-i-p device structures whose efficiency ranges between 14.20% and 22.77% respectively. The influence of varying the work function of back contact, series resistance, shunt resistance, and temperature on the photovoltaic parameters was analysed. The vital parameters investigated in this simulation for implementing state-of-the-art PCS are energy band offset, diffusion length, activation energy, recombination current profile, and built-in-potential. The device configuration featured with SrTiO3/MASnI3/CuO and SrTiO3/MASnI3/MASnBr3 achieved a maximum efficiency of 22.77% and 22.60%, respectively. The PSC tailored with SrTiO3 have better thermal stability and enhanced fill factor, which accounts for improving the output power. These novel findings of all-inorganic PSC will provide preliminary support for practical implementation.

Benchmarking the yttrium content in the low temperature/low humidity electrical properties of yttrium-doped barium cerate

Yttrium-doped barium cerate (BCY) is one of the best proton-conducting ceramics to be used in fuel cells/electrolyzers at intermediate temperatures, due to its high hydration enthalpy and high conductivity. Nonetheless, it has commonly been discarded for these applications due to its instability in the presence of carbonaceous and humidified atmospheres. A recent work has addressed this issue, by suggesting the use of this material in very low water vapor partial pressures (pH2O ∼ 10−4 atm) [Electrochimica Acta 334 (2020) 135625] and at low temperatures (T ≤ 400 °C). Under these conditions, BCY can still offer pure protonic conductivity while also offering suitable stability. In the current work, we provide a comprehensive analysis of the effects of the acceptor dopant concentration (Y2O3) in the structural, microstructural, and electrical properties in a wide compositional series of BaCe1-xYxO3-δ (x = 0.05, 0.10, 0.20 and 0.30) at low levels of humidity in the low temperature range (100–400 °C). The results show that BaCe0.9Y0.1O3-δ (BCY10) offers the highest bulk conductivity in these conditions, while further increase in dopant concentration leads to impairment due to “proton trapping” effects. In contrast, the specific grain boundary conductivity increases with increasing dopant concentration due to a reduction of Schottky barrier height at the space-charge layer. We demonstrate that, by operating at very low temperatures (e.g., below 400 °C), the peak performing, BCY10 material can still operate at very low levels of water vapor partial pressure (pH2O ∼ 10−4 atm), where its stability can be maintained. This work paves the way for the optimization of this material, with a focus on utilizing low humidity levels and low temperatures, where it can offer a competitive advantage over that of the majority of other proton-conducting perovskites for potential applications operating under these conditions.

Grain growth and segregation in Fe-doped SrTiO3: Experimental evidence for solute drag

In functional ceramics, the impact of dopants on bulk crystals is generally well understood. Their impact on grain boundaries is less well known. The present study investigates the impact of acceptor dopants on grain growth in strontium titanate. Scanning electron microscopy and analytical (scanning) transmission electron microscopy have been used to gain knowledge on Fe segregation behavior, grain sizes, and grain size distributions of SrTiO3. While undoped microstructures show normal grain growth at low temperatures (<1350 °C), doped microstructures evolve bimodally. With increasing acceptor dopant concentration, an increasing population of small grains develops. It is shown that Fe segregates to the grain boundaries due to its negative charge and a positive boundary potential. Thus, the experimental findings seem to be well explained by the theory of solute drag: The diffusion of segregated defects (‘solutes’) at grain boundaries can retard grain boundary migration.

Replacing the Electron-Hole Transport Layer by Doping: Optimization of Tin-Based Perovskite Solar Cells from a Simulation Perspective

Due to their non-toxic nature and good charge transport properties, tin-based perovskite solar cells are gaining attention. Here, we used SCAPS-1D (Solar Cell Capacitance Simulator) to simulate and analyze constructed devices. We then created n-MASnI3 and p-MASnI3 layers that facilitate electron-hole transport by changing the doping concentration of MASnI3 in the perovskite absorber layer, replacing the conventional electron transport layer (ETL) and hole transport layer (HTL). This simplifies the manufacturing process to reduce cost and realize the conversion of lead-free perovskite solar cells. By studying the thickness of n-MASnI3 and p-MASnI3, and the acceptor and donor doping concentrations (ND and NA), we explored the effects on each device performance parameter in terms of energy band distribution, recombination rate variation, and external quantum efficiency. The first optimization of the electron transport layer and hole transport layer was thereby achieved. A second optimized analysis of the doping concentration of i-MASnI3 absorber layer was achieved. Finally, we optimized the device performance parameters as V OC = 0.8827 V, J SC = 23.1720 mA cm−2, FF = 63.1390% and PCE = 12.9144%.

Simulation Based Investigation on the Performance of Metal Oxides as Charge Transport Layers in Lead/Tin Perovskite Solar Cells Using SCAPS 1D

Perovskite solar cells have been in the lime-light of emerging photovoltaic technology owing to their rapid rise in efficiency. The solar capacitance simulator (SCAPS −1D) is a simulation tool that can be used to investigate on the factors that affect the performance of planar perovskite solar cells. In this work, a simulation model has been developed to investigate the performance of metal oxides as charge transport layers for lead and tin based perovskite solar cells. The simulation study on the optimization of energy band gap and electron affinity of ZnO electron transport material with lead/tin perovskite using inorganic metal oxide Cu2O as hole transport materials is done. The influence of trap defect density (Nt) and acceptor doping concentration (Na) of the perovskite layer on the solar cell performance is also evaluated. The doping concentration and defect density of the perovskite layer greatly influence the recombination rate which determines the efficiency of perovskite solar cell.The common p type metal oxides CuO and NiO are experimented for the perovskite solar cell using lead/tin perovskite. The simulation results prove Cu2O as the best metal oxide hole transport material that can be utilized for efficient ZnO based perovskite solar cells.

Numerically investigating the AZO/Cu2O heterojunction solar cell using ZnO/CdS buffer layer

Aluminium (Al)-doped zinc oxide (ZnO)/copper oxide (AZO/Cu2O) heterojunction solar cell is analyzed by a 1-D solar cell capacitance simulator (SCAPS-1D). The influence of single (CdS) and double (ZnO and CdS) buffer layers on the performance of AZO/Cu2O heterojunction solar cells is studied. The effects of device parameters such as Cu2O acceptor and CdS donor doping concentrations, external quantum efficiency, interface states density, metal work function, absorber and buffer layer thicknesses, and working temperature on both single and double buffer layer solar cell are carried out. The optimized solar cell structure of single buffer AZO/CdS/Cu2O/Au and double buffer AZO/ZnO/CdS/Cu2O/Au results in the power conversion efficiency (PCE) of 10.47 and 10.60 %, short circuit current density (JSC) of 11.33 and 11.37 mA cm−2, open-circuit voltage (Voc) of 1.1381 and 1.1405 V and fill factor (FF) of 81.21 and 81.74 %, respectively under illumination. Our findings reveal that the PCE of AZO/Cu2O based heterojunction thin-film solar cell is enhanced through the usage of a double buffer (ZnO/CdS) layer in comparison to the single (CdS) buffer layer.

Simulation on Optimum Doping Levels in Si Solar Cells

The two key variables of an Si solar cell, i.e., emitter (n-type window layer) and base (p-type substrate) doping levels or concentrations, are studied using Medici, a 2-dimensional semiconductor device simulation tool. The substrate is ptype and 150 μm thick, the pn junction is 2 μm from the front surface, and the cell is lit on the front surface. The doping concentration ranges from 1 × 1010 cm−3 to 1 × 1020 cm−3 for both emitter and base, resulting in a matrix of 11 by 11 or a total of 121 data points. With respect to increasing donor concentration (Nd) in the emitter, the open-circuit voltage (Voc) is little affected throughout, and the short-circuit current (Isc) is affected only at a very high levels of Nd, exceeding 1 × 1019 cm−3, dropping abruptly by about 12%, i.e., from Isc = 6.05 × 10−9 A·μm−1, at Nd = 1 × 1019 cm−3 to Isc = 5.35 × 10−9 A·μm−1 at Nd = 1 × 1020 cm−3, likely due to minority-carrier, or hole, recombination at the very high doping level. With respect to increasing acceptor concentration (Na) in the base, Isc is little affected throughout, but Voc increases steadily, i.e, from Voc = 0.29 V at Na = 1 × 1012 cm−3 to 0.69 V at Na = 1 × 1018 cm−3. On average, with an order increase in Na, Voc increases by about 0.07 V, likely due to narrowing of the depletion layer and lowering of the carrier recombination at the pn junction. At the maximum output power (Pmax), a peak value of 3.25 × 10−2 W· cm−2 or 32.5 mW· cm−2 is observed at the doping combination of Nd = 1 × 1019 cm−3, a level at which Si is degenerate (being metal-like), and Na = 1 × 1017 cm−3, and minimum values of near zero are observed at very low levels of Nd ≤ 1 × 1013 cm−3. This wide variation in Pmax, even within a given kind of solar cell, indicates that selecting an optimal combination of donor and acceptor doping concentrations is likely most important in solar cell engineering.

Numerical modeling and simulation for augmenting the photovoltaic response of HTL free perovskite solar cells

Organo-metal halide perovskites have drawn a lot of appeal from the research community in recent years because of its application as an absorber in thin-film solar cells. However, the fabrication of multi-layered defect-free planar perovskite solar cell (PSC) structures is a very challenging task. This is because the interface between charge transport layer/perovskite materials promotes hysteresis and recombination leading to poor long term stability. Along with the mechanism of charge transport, the dependence of performance on the material parameters in hole transport layer (HTL)-free PSCs is unclear. Removal of the HTL layer from the standard configuration in PSC degrades the device performance. In this paper, a novel HTL-free PSC employing glass/FTO/TiO2/CH3NH3Pb(I1-xBrx)3/Au contact structure has been investigated using a one-dimensional modeling program AMPS-1D. It was demonstrated that to achieve better photovoltaic performance, the thickness of the absorber should be increased; the acceptor doping concentration should be of the order of ∼ 1017 and the bandgap should be modified to 1.7 eV. Under moderate simulation conditions, if the above factors are satisfied, efficiencies over 17% can be attained.

Theoretical study of graded bandgap CZTSSe solar cells with two absorber layers

In this work, new Cu2ZnSn(S1−x, Sex)4 (CZTSSe) solar cells consisting of two absorber layers with constant and graded bandgaps are proposed. CZTS and CZTSe are used as the constant bandgap absorbing layers of the first and second proposed cells, respectively. To validate the simulations, first, a graded bandgap CZTSSe-based cell containing AZO/ZnO/CdS/CZTSSe/MoSe2/Mo layers as the basic structure is investigated, revealing that the results are in good agreement with previous experimental data. The impact of varying acceptor doping concentration and temperature on the performance of proposed cells is investigated. The optimum thicknesses of the absorber layers are obtained in all cases. After optimization, maximum efficiencies of 20.99% and 21.37% are obtained for the first and second cells respectively which are significantly greater than the basic structure. The proposed structures provide higher open circuit voltage and short circuit current, compared to the basic structure.

Modeling and optimization of n-c-AlGaAs/p-c-GaAs solar cells

The main of our work is to establish a model which enables us to predicate an improvement for solar cells efficiencies elaborated by hetero-structures compounds; we focused our optimization by simulation on an n-c-AlGaAs/p-c-GaAs solar cell with back surface field (BSF), which is a p/p+ (Low-High) junction. This junction creates a potential barrier which avoid speedy recombination of minor careers (electron in the base), however all the main parameters which have large impact on the short circuit current density, on the open circuit voltage, on the fill factor and on the conversion efficiency were discussed in this work. Generally the electrical conversion is function of the acceptor and donor doping concentrations, of the cell emitter and the base thicknesses, of the surface recombination velocity at front and back contacts and of careers live times (for electrons and holes). The effects of the discontinuities occurring in the energies bands clause to the interface were taken into consideration too.Under A.M 1.5 illumination, our calculations results reveal an efficiency of 23.80% for the optimum parameters (Nd = 5 × 1018 cm−3, Na = 5 × 1017 cm−3, JSC = 25.77 mA/cm², VOC = 0.985 V, Sf = 104 cm/s and Sb = 108cm/s). It seems that this simulated device can be used in cell concentrations utilities and, it presents an efficiency of 29.28% under 100 A.M 1.5. Finally, based on these attempts, the n-c-AlGaAs/ p-c-GaAs structure is suggested as promising solar cell applications and the actual model is intended to be extended to multilayer solar cells.

Elucidating the role of interfacial MoS2 layer in Cu2ZnSnS4 thin film solar cells by numerical analysis

In this study, the effects of transition metal dichalcogenide, MoS2 interfacial layer formation between the Cu2ZnSnS4 (CZTS) absorber layer and Mo back contact in a conventional CZTS thin film solar cell (TFSC) structure have been studied by numerical simulation using wxAMPS-1D software. The goal of this study is to elucidate the effects of both n and p-type MoS2 on the overall CZTS solar cell’s performance from the viewpoint of metal-semiconductor junction and heterojunction band alignment. Interestingly, CZTS device, regardless of p or n-type MoS2 largely outperforms device without any MoS2 due to lower back contact barrier value. Significant transition in efficiency is noticed when acceptor (increases efficiency) or donor (decreases efficiency) concentration has a transition from 1016 cm−3 to higher concentration of 1018 cm−3 or more. Also, effect of variable electron affinity and band gap of MoS2 has been discussed from band alignment perspective. Generally, MoS2 layer with lower electron affinity and band gap is preferred to induce desirable band alignment and subsequently result in higher efficiency. All-in all, the formation of p-type MoS2 in CZTS solar cells can be tuned to improve the cell performance mainly by doping with higher acceptor doping concentration and limiting layer thickness. However, the detrimental effect of n-MoS2 can be prevented by maintaining thinner layer in the vicinity of ∼30 nm with low to moderate donor doping (<1016 cm−3).

The role of point defects and defect gradients in flash sintering of perovskite oxides

The present study investigates the impact of point defects and their redistribution on the flash sintering process. Strontium titanate was chosen as a model system for the group of perovskite ceramics. The characteristics of flash sintering of strontium titanate were analyzed with different acceptor dopant concentrations. The onset of flash sintering was found to be dependent on the acceptor dopant concentration, as expected by the increasing conductivity. A gradient in the microstructure was found after flash sintering with larger grain sizes at the negative electrode. TEM-EDS measurements indicated Ti enrichment at the positive electrode for undoped strontium titanate and strong acceptor segregation for doped strontium titanate. In contrast, grain boundaries at the negative electrode were found to be stoichiometric for the undoped case and the acceptor segregation was less obvious for the doped case.Based on these results and the space charge behavior of strontium titanate, we infer that a gradient of the oxygen vacancy concentration is induced by the electric field during flash sintering: at the positive electrode the oxygen vacancy concentration is higher than at the negative electrode. For strontium titanate it is well known that a high oxygen vacancy concentration reduces the space charge and, hence, acceptor segregation, which agrees well with the experimental findings. Overall, the present study highlights the importance of point defect gradients and space charge for flash sintering of strontium titanate, which may be applicable for many other functional ceramics.

Solid solution limits and electrical properties of scheelite SryLa1-yNb1-xVxO4-δ materials for x = 0.25 and 0.30 as potential proton conducting ceramic electrolytes

The proton conductivity and solid solubility limits of acceptor strontium doped vanadium stabilised lanthanum niobate (SryLa1−yNb1-xVxO4-δ, x = 0.25, 0.30 and y = 0 to 0.10) were explored as potential proton conducting ceramic electrolytes. All samples were synthesized via a solid-state method. The phase purity, microstructure and thermal expansion behaviour of the materials were studied using powder X-ray diffraction, scanning electron microscopy and dilatometry, respectively. A maximum solid solution limit of 5% Sr in the A-site of SryLa1−yNb1-xVxO4-δ samples is observed for a vanadium content of x = 0.25, while further increases in the Sr or vanadium contents lead to the presence of Sr3(VO4)2 as a secondary phase. This acceptor dopant content of 5%Sr in the current scheelite material exceeds that possible in the parent vanadium-free fergusonite SryLa1−yNbO4-δ material by a factor of 5. All Sr doped scheelite materials show linear thermal expansion behaviour, successfully avoiding the scheelite to fergusonite structural phase change during thermal cycling. The average grain size is shown to be increased by increasing vanadium content. In humid conditions, all phase pure samples show predominantly proton conductivity at lower temperatures, while p-type conductivity is noted at higher temperatures under dry oxidising conditions. In the low temperature range, the Sr0.05La0.95Nb0.75V0.25O4-δ sample, containing the largest acceptor dopant concentration, exhibits slightly higher bulk and specific grain boundary conductivities in comparison to other phase pure compositions.

Simulation study of the n-c-Si(Sb)/p-c-Si structure suitable for solar cells devices

In this work, we have optimized by simulation a solar cell n-c-Si(Sb)/p-c-Si structure, which is obtained by the recoil implantation of antimony (Sb) in crystalline silicon (c-Si). However the parameter structures (emitter thickness (Xj) for n-c-Si(Sb) layer, base thickness (Xb) for p-c-Si layer, donor doping concentration (Nd) and acceptor doping concentration (Na)) which have influences on the main solar cell characteristics like short-circuit current (JSC), open-circuit voltage (VOC), fill factor (FF) and efficiency (Eff) was taken into account. We suggest that a such component is more stable against unknown damages and will present a long life due to the annealing treatment at a high temperature (850°), which gives it a good stability. By using numerical method, all calculations have been carried out by developing a model to predicate the output parameters of the present pretended solar cell. Accordingly, with optimized structure parameters (Na = Nd = 1017 cm −3, Xj range from 0.05 to 0.1 μm and Xb = 300 μm) such solar cell presents an efficiency of 17.00% for AM 1.5 and 22.11% under sun concentration. For these reasons, the n-c-Si(Sb)/p-c-Si structure is considered as a promising solar cell component.