Behavior of Bombarded Solar Cells Made from Various Silicon Materials
Radiation effects on boron and aluminum doped silicon solar cells and phenomenon of reverse annealing in boron-doped silicon cells
SOLAR CELL↗
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Influence of Annealing on Microstructure, Electrochemical, and Magnetic Properties of Co-Doped SrTiO{sub 3} Nanocubes
Effect of annealing on microstructure, electrochemical, and magnetic properties of Co-doped SrTiO{sub 3} nanocubes obtained by the hydrothermal method was studied. X-ray diffraction (XRD) results of all as-prepared and annealed Co-doped SrTiO{sub 3} samples revealed a cubic perovskite structure with the second phases of SrCO{sub 3} and Co{sub 3}O{sub 4}in as-prepared and annealed SrTi{sub 0.90}Co{sub 0.10}O{sub 3} samples, respectively. Agglomerated nanocubes could be clearly observed in all as-prepared and annealed Co-doped samples by scanning electron microscope (SEM) and transmission electron microscope (TEM). X-ray absorption near edge spectroscopy (XANES) results suggested the presence of Co{sup 2+} cations in as-prepared Co-doped SrTiO{sub 3} samples, while both of Co{sup 2+} and Co{sup 3+} cations were found in annealed Co-doped SrTiO{sub 3} samples. The cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) results of as-prepared and annealed SrTi{sub 1-x}Co{sub x}O{sub 3} (x = 0.05, 0.075 and 0.10) electrodes revealed pseudocapacitor behavior of the Faradaic redox reaction type. The specific capacitance (Csc) was affected by the increase of Co content in all as-prepared and annealed Co-doped SrTiO{sub 3} samples with an excellent cycling stability after 200 cycle test of 97.24% and the highest value of 75.28 F g{sup −1} at 1 A g{sup −1} in an annealed SrTi{sub 0.925}Co{sub 0.075}O{sub 3} electrode. Magnetization measurements at room temperature using vibrating sample magnetometer (VSM) revealed diamagnetic behavior of as-prepared SrTiO{sub 3} sample, whereas paramagnetic behavior was observed in all as-prepared Co-doped SrTiO{sub 3} samples. After annealing, undoped sample exhibited paramagnetic behavior, whereas ferromagnetic behavior was observed in all Co-doped SrTiO{sub 3} samples with the increase of saturation magnetization (M{sub s}) at 10 kOe from 0.58 to 1.63 emu/g and the coercive field (H{sub c}) from 43.71 to 123.87 Oe, suggested to originate from the face-center exchange (FCE) mechanism.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Effect of Y{sub 2}BaCuO{sub 5} Nanoparticle Doping on Critical Current Density of YBa{sub 2}Cu{sub 3}O{sub 7-δ} Bulk Superconductor
This study presents the effect of Y{sub 2}BaCuO{sub 5} (Y211) nanoparticle doping on critical current density and critical temperature of YBa{sub 2}Cu{sub 3}O{sub 7-δ} (YBCO) superconductor. Y211 nanoparticles with different particle sizes ranging from 34 to 455 nm were synthesized by a sol-gel method, then doped into the YBCO superconductor by 0.5, 1, and 2 wt.%. Samples were characterized using X-ray diffraction and scanning electron microscope measurements. The standard four-probe technique was used to measure the critical current density at 77 K. The results showed that in the all-doped samples, critical current density was higher than that of the pure sample. It was found that in the samples containing 1 and 2 wt.% of Y211 nanoparticles, by increasing the size of nanoparticles, the J{sub c} was increased, but in samples containing 0.5 wt.%, the J{sub c} decreased. The maximum critical current density of 64 A/cm {sup 2} was obtained for the samples doped with 2 wt.% of 455 nm Y211 nanoparticles. Also, it was observed that the critical temperature slightly decreased with nanoparticle doping.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Elastic and thermodynamic properties of cerium-doped yttrium aluminum garnets
Cerium-doped yttrium aluminum garnets (Y 3-x Ce x Al 5 O 12 , Ce:YAGs) are promising yellow light-emitting components of solid-state white light-emitting diodes. Although there have been numerous studies examining the effects of Ce concentrations on the luminescent properties of Y 3-x Ce x Al 5 O 12 , the impacts of Ce dopant on the elastic and thermodynamic properties are not well understood. In this work, we used resonant ultrasound spectroscopy (RUS) to determine the effects of Ce doping (0.025, 0.1, 1 at. %) on the elastic and thermodynamic properties of Y 3-x Ce x Al 5 O 12 . The elastic moduli calculated via the Voigt–Reuss–Hill (VRH) method demonstrated that low Ce dopant concentrations (≤0.1 at. %) induced negligible effects on the elasticity of the YAG host matrix, while a high Ce concentration (1 at. %) yielded significant softening. RUS spectral analysis and SEM images suggested that the elastic softening originated from microstructural differences induced at higher Ce dopant concentrations. Additionally, we demonstrated an increase in elastic anisotropy at higher Ce concentrations, which further elucidated the correlations between structure and elasticity of Y 3-x Ce x Al 5 O 12 . Debye temperatures ($θ_D$), heat capacities ($C_p$), and thermal conductivities ($\mathit{κ}$) were calculated for Ce:YAGs through the relations of RUS-derived parameters (sound velocities, elastic moduli) and previously determined thermal expansion coefficients. Ce:YAG was found to have a significant reduction in $θ_D$, Cp, and $\mathit{κ}$ at Ce concentrations ≥1 at. %. Lastly, extrapolation of $C_p$ and $\mathit{κ}$ to higher temperatures allowed the modeling of thermal stress experienced by Y 3-x Ce x Al 5 O 12 disks up to 1073.15 K.
36 MATERIALS SCIENCE↗
Interstitial Lithium Doping in BiVO4 Thin Film Photoanode for Enhanced Solar Water Splitting Activity
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99 GENERAL AND MISCELLANEOUS↗
Electronic and transport properties of Li-doped NiO epitaxial thin films
NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. Understanding and improving its optical and transport properties have been of considerable interest. In this work, we have investigated the effect of Li doping on the electronic, optical and transport properties of NiO epitaxial thin films grown by pulsed laser deposition. We show that Li doping significantly increases the p-type conductivity of NiO, but all the films have relatively low room-temperature mobilities (<0.05 cm2 V -1 s -1 ). The conduction mechanism is better described by small-polaron hoping model in the temperature range of 200 K < T <330 K, and variable range hopping at T <200 K. A combination of x-ray photoemission and O K-edge x-ray absorption spectroscopic investigations reveal that the Fermi level gradually shifts toward the valence band maximum (VBM) and a new hole state develops with Li doping. Both the VBM and hole states are composed of primarily Zhang-Rice bound states, which accounts for the small polaron character (low mobility) of hole conduction. Our work provides guidelines for the search for p-type oxide materials and device optimization. NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. This work reports the controlling of conductivity and increase of work functions by Li doping.
Environmental Molecular Sciences Laboratory↗
Accelerated Modeling of Lithium Diffusion in Solid State Electrolytes using Artificial Neural Networks
Abstract Previous efforts to understand structure‐function relationships in high ionic conductivity materials for solid state batteries have predominantly relied on density functional theory (DFT‐) based ab initio molecular dynamics (MD). Such simulations, however, are computationally demanding and cannot be reasonably applied to large systems containing more than a hundred atoms. Here, an artificial neural network (ANN) is trained to accelerate the calculation of high accuracy atomic forces and energies used during such MD simulations. After carefully training a robust ANN for four and five element systems, nearly identical lithium ion diffusivities are obtained for Li 10 GeP 2 S 12 (LGPS) when benchmarking the ANN‐MD results with DFT‐MD. Applying the ANN‐MD approach, the effect of chlorine doping on the lithium diffusivity is calculated in an LGPS‐like structure and it is found that a dopant concentration of 1.3% maximizes ionic conductivity. The optimal concentration balances the competing consequences of effective atomic radii and dielectric constants on lithium diffusion and agrees with the experimental composition. Performing simulations at the resolution necessary to model experimentally relevant and optimal concentrations would be infeasible with traditional DFT‐MD. Systems that require a large number of simulated atoms can be studied more efficiently while maintaining high accuracy with the proposed ANN‐MD framework.
Rao, Karun K.↗
Self-regulating surface chemistry for more robust highly durable solid oxide fuel cell cathodes
In this project we explored the possibility of mitigating silicon poisoning of Pr doped ceria (PCO) electrodes for oxygen reduction in SOFC. The approach was to dope PCO with various amount of lanthanum and study the new compositions in terms of their mixed conduction properties, their oxygen surface exchange kinetics, as well as their resistance to silicon poisoning. The effects of lanthanum doping on the transport properties and oxygen exchange kinetics of La x (Ce 0.9 Pr 0.1 ) 1-x O 2-δ (x=0, 0.1 and 0.2) have been investigated by electrical conductivity on bulk samples and optical relaxation on thin films respectively. Lanthanum substitution was observed to increase the magnitude of ionic conductivity to values comparable to that of single substituted La x Ce 1-x O 2-δ , with a maximum for a La content of x = 0.1, reaching σ = 9.5×10 -3 S·cm -1 at 600 °C and a decrease in activation energy from ≈ 1 eV for Ce 0.9 Pr 0.1 O 2-δ down to ≈ 0.75 eV for the lanthanum substituted compositions. At the same time, a significant electronic contribution to the total conductivity, estimated to be on the order of 10%, supports significant mixed ionic-electronic conductivity.
08 HYDROGEN↗
Luminescence Quenching in Magnesium-Doped Alumina Ceramics
The effect of magnesium impurity on luminescent properties of alumina ceramics sintered at high temperatures under vacuum is studied by pulsed cathodoluminescence, photoluminescence, and thermoluminescence. At dopant concentrations >1 wt %, high-temperature synthesis results in formation of defects associated with magnesium, which were identified in the pulsed cathodoluminescence (520 nm) and photoluminescence (767 nm) spectra, as well as in the thermoluminescence curves (380 K). It is found that increased magnesium concentration leads to luminescence quenching of the intrinsic centers (F centers) of alumina in the PCL emission band at 400 nm, impurity defects (Mn{sup 4+} and Cr{sup 3+}) in the photoluminescence emission bands at 673 and 689 nm, and all the recorded thermoluminescence peaks at 380, 450, and 615 K.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Revealing the Structure of Single Cobalt Sites in Carbon Nitride for Photocatalytic CO 2 Reduction
Single Co 2+ sites in graphitic carbon nitride (C 3 N 4 ) have demonstrated excellent activity and selectivity in photocatalytic CO 2 reduction. In this work, we combine computational and spectroscopic tools, including X-ray absorption spectroscopy, to probe the structure of such single Co 2+ sites. Our results indicate that the Co 2+ sites exist in the Co–N 2+2 coordination at the edges of C 3 N 4 flakes. This mode of coordination is further supported by experimental results obtained using single Co 2+ sites in C 3 N 4 materials treated with NH 3 , which contain more edge sites than untreated C 3 N 4 . In our experimental observations, doping C 3 N 4 with carbon is found to be important for the photocatalytic properties of the single Co 2+ sites. Here, a simplified model is proposed to explain the origin of the observed enhancement effect of C doping. In this model, the presence of C dopant near the metal centers results in shorter Co–N bond length and stronger Co–N binding energy. In addition to enhanced light absorption and charge separation in C-doped C 3 N 4 , the stronger Co–N binding upon C doping likely contributes to the improved catalytic properties of the single Co 2+ sites.
14 SOLAR ENERGY↗
Electronic and magnetic properties of hole-doped topological kagome Fe 1−𝑥 Mn 𝑥 Sn thin films
We have investigated the electronic and magnetic structures of topological kagome Fe 1−𝑥 Mn 𝑥 Sn (0 ≤ 𝑥 ≤ 0.3) thin films via neutron diffraction, electronic transport measurements, and ab initio density functional theory (DFT) to understand the interplay between hole doping, magnetism, and the electronic structures. Temperature-dependent neutron diffraction measurements on parent FeSn reveal the Néel temperature to be 𝑇 N ∼ 355 K and the underlying A-type antiferromagnetic ordering is associated with a wave vector 𝒒 = (001/2). Upon Mn doping to 𝑥 = 0.15, 𝑇 N decreases slightly while the magnetic ordering vector remains the same. Resistivity measurements show metallic characteristics and in-plane anisotropy down to 10 K for all the investigated samples. The effects of hole doping are mapped in terms of electronic ground state calculations via DFT which show that the Dirac point is moved closer to the Fermi level (𝐸 F ) and the flat bands get pushed away from 𝐸 F upon hole doping. However, a comparison between hole-doped Fe 1−𝑥 Mn 𝑥 Sn and electron-doped Fe 1−𝑥 Co 𝑥 Sn indicates that the Néel temperature does not scale with the position of 𝐸 F relative to the flat band. Furthermore, our results establish the antiferromagnetic state of FeSn and Fe 1−𝑥 Mn 𝑥 Sn films at room temperature, laying the groundwork for future studies of magnetism in kagome heterostructures.
36 MATERIALS SCIENCE↗
Hydrated doped-BaZrO 3 proton conductors studied by positron annihilation lifetime spectroscopy
The study of defect chemistry for doped BaZrO 3 proton conductors is of particular interest because of defect interactions that can affect the proton conductivity of the material. Protons incorporated due to the material's hydration can be trapped by negatively charged immobile dopants, reducing proton mobility. The reduction of the proton conduction impedes using BaZrO 3 materials in energy conversion applications at intermediate temperatures (300°C – 600°C). The probing of proton trapping in doped BaZrO 3 is hindered by the limited availability of techniques sensitive to defect chemistries. In this work, we used positron annihilation lifetime spectroscopy (PALS) to study the defect chemistry of Y-doped and Sc-doped BaZrO 3 . Using a two-state positron trapping model we showed that PALS can be used to study the defect chemistry of hydrated dense proton conductors. Positron trapping rates and lifetimes were correlated with doping levels of the materials. Probability significance t-tests were carried out for PALS parameters to verify whether there are differences/similarities for various populations: non-doped/doped, level and type of doping, high temperature, and surface effects. Further, the results revealed that the initial doping generates a significant number of traps available for positrons. Doping in yttrium increased the positron trapping rate, while this effect was not observed with scandium. Low-temperature hydration affects specimens significantly inhibiting positron trapping at undoped BaZrO 3 material and highly doped specimens. Positronium formation in rough surface layers, and highly doped specimens was detected but does not exceed 1%.
36 MATERIALS SCIENCE↗
Tuning phase stability and short-range order through Al doping in ( CoCrFeMn ) 100 - x A l x high-entropy alloys
For ( CoCrFeMn ) 100 - x A l x high-entropy alloys, we report on the phase evolution with increasing Al content ( 0 ≤ x ≤ 20 at.%). From first-principles theory, aluminum doping drives the alloy structurally from fcc to bcc separated by a narrow two-phase region (fcc+bcc), which is well supported by our experiments. Using KKR-CPA electronic-structure calculations, we highlight the effect of Al doping on the formation enthalpy (alloy stability) and electronic dispersion of ( CoCrFeMn ) 100 - x A l x alloys. As chemical short-range order indicates the nascent local order, and entropy changes, as well as expected low-temperature ordering behavior, we use KKR-CPA-based thermodynamic linear response to predict the chemical ordering behavior of arbitrary complex solid-solution alloys—an ideal approach for predictive design of high-entropy alloys. The predictions confirm our present experimental findings and other reported ones.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
β -Ga 2 O 3 MESFETs with insulating Mg-doped buffer grown by plasma-assisted molecular beam epitaxy
In this work, we develop in situ Mg doping techniques in plasma-assisted molecular beam epitaxy (PAMBE) of β -Ga 2 O 3 to compensate Si dopants at the substrate epilayer growth interface and eliminate parasitic leakage paths. Both abrupt and uniform Mg doping profiles over a wide range of concentrations were achieved in β -Ga 2 O 3 epilayers grown by PAMBE. Capacitance–voltage characteristics of Si and Mg co-doped samples confirmed the compensating effect of the Mg dopants. Mg delta-doping was then integrated into a β -Ga 2 O 3 metal-semiconductor field effect transistor structure and shown to be effective in eliminating source leakage. In conclusion, the results presented here show that Mg doping is a promising way to engineer insulating buffer layers for β -Ga 2 O 3 lateral devices grown by PAMBE.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Robust antiferromagnetic spin waves across the metal-insulator transition in hole-doped BaMn 2 As 2
BaMn 2 As 2 is an antiferromagnetic insulator where a metal-insulator transition occurs with hole doping via the substitution of Ba with K. The metal-insulator transition causes only a small suppression of the Néel temperature (T N ) and the ordered moment, suggesting that doped holes interact weakly with the Mn spin system. Powder inelastic neutron scattering measurements were performed on three different samples of Ba 1 - x K x Mn 2 As 2 with x = 0 , 0.125, and 0.25 to study the effect of hole doping and metallization on the spin dynamics. We compare the neutron intensities to a linear spin-wave theory approximation to the J 1 $-$ J 2 $-$ J c Heisenberg model. Hole doping is found to introduce only minor modifications to the exchange energies and spin gap. Lastly, the changes observed in the exchange constants are consistent with the small drop of T N with doping.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Antiferromagnetism in Co-57-doped La2CuO(4-y) studied by Moessbauer spectroscopy
Moessbauer effect studies of Co-57-doped La2CuO(4-y) were performed at temperatures between 4.2 K and room temperature. These confirm the antiferromagnetic ordering of these compounds below room temperature. Temperature dependence of the quadrupole splitting shows that the hyperfine field is at an angle with the c-axis.
Jha, S.↗
Solution-based electrical doping of semiconducting polymer films over a limited depth
Solution-based electrical doping protocols may allow more versatility in the design of organic electronic devices; yet, controlling the diffusion of dopants in organic semiconductors and their stability has proven challenging. Here we present a solution-based approach for electrical p-doping of films of donor conjugated organic semiconductors and their blends with acceptors over a limited depth with a decay constant of 10–20 nm by post-process immersion into a polyoxometalate solution (phosphomolybdic acid, PMA) in nitromethane. PMA-doped films show increased electrical conductivity and work function, reduced solubility in the processing solvent, and improved photo-oxidative stability in air. Here, this approach is applicable to a variety of organic semiconductors used in photovoltaics and field-effect transistors. PMA doping over a limited depth of bulk heterojunction polymeric films, in which amine-containing polymers were mixed in the solution used for film formation, enables single-layer organic photovoltaic devices, processed at room temperature, with power conversion efficiencies up to 5.9 ± 0.2% and stable performance on shelf-lifetime studies at 60 °C for at least 280 h.
36 MATERIALS SCIENCE↗
Combinatorial Platform for Discovery of Nanocrystal-Ink Based Earth Abundant Element PV with Efficiency Greater than 20%
(1) We successfully developed an ultrasonic spray coating system that can be used to deposit thin chalcogenide films with composition gradients. 4 publications under the contract have been published with the instrument. The instrument was used to reveal the effects of intrinsic composition and examine the effects of 25 different dopant elements. Surprisingly, doping with most elements had little to no effect on the quasi-Fermi level splitting of bare films. Ge and Li were explored in depth, and our best devices utilize lithium doping. (2) We developed a new model of absorption coefficients, that when combined with absolute intensity photoluminescence, yield the steady-state quasi-Fermi level splitting and a way to quantify the sub-bandgap absorption. This has resulted in 2 publications on the method, with another in preparation. This is a significant development that should impact other PV technologies. (3) We found that lithium doping has several beneficial effects on CZTSSe. It improves the open-circuit voltage, short circuit current, fill factor, and shunt resistance. By using scanning Kelvin probe microscopy (SKPM) and conductive AFM (along with device measurements, DLPC, and XPS), we discovered that lithium acts to increase the p-type doping in both the grain and grain boundaries (GBs). The effect is stronger in the GBs and changes the direction of the electric field at the GB. In lithium doped devices, an electric field repels minority carrier electrons away from the GB. This resulted in a publication and the fabrication of 11.8% efficient devices from a DMSO-thiourea molecular ink. The mechanism of action is most likely due to the formation of LiCu, which inhibits the formation of the donor defect ZnCu. This reduces compensation and increases the net p-type doping. (4) By alloying with germanium, we have fabricated CZTGSSe devices with the best open-circuit voltage (relative the maximum theoretical open-circuit voltage for the bandgap) for any kesterite solar cell. The Voc/Voc,max is 63%, compared to 58% for the record efficiency cell from hydrazine. The origin of the increased voltage efficiency appears to be related to the conduction band off-set and the suppression of a deep defect (~0.8 eV), most likely due to CuSn, but SnZn or SnCu are also possible. All milestones and go/no-go metrics were met with exception of the device efficiency milestone (15% then 20%). However, under the contract, hydrazine-free CZTSSe device efficiencies increased from 7.2% at the start of the contract to 11.8% upon completion.
14 SOLAR ENERGY↗