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Electron contact interlayers for low temperature processed crystalline silicon solar cells
Get PDFThis study focuses on electron selective passivating contacts for crystalline silicon c Si solar cells where an interlayer is used to provide a low contact resistivity between the c Si substrate and the metal electrode. These electron contact interlayers are used in combination with other passivating interlayers e.g., a Si H, TiOx, and Nb2O5 to improve surface passivation whilst still permitting contact resistivities suitable for high efficiency solar cells. We show that a wide variety of thermally evaporated materials, most of which have ionic character, enable an Ohmic contact between n type c Si and Al. From this pool of compounds, we observed that CsBr has especially promising behavior because of its excellent performance and thermal stability when combined with thin passivating layers. With different test structures, we were able to demonstrate low contact resistance using TiOx CsBr, Nb2O5 CsBr, and a Si H CsBr stacks on n type c Si. The quality of the provided surface passivation depended on the stack but we achieved the best overall passivation stability with TiOx CsBr. Finally, we were able to demonstrate an efficiency gt;20 on a laboratory scale solar cell that implements the TiOx CsBr Al stack as full area rear side electron selective contac
Low Resistivity Sputter Deposited SnOx Thin Films An Indium Free Transparent Conductive Oxide?
Get PDFThis study investigates the influence of oxygen concentration and thermal treatment on the optical and electrical properties of tin oxide SnOx thin films deposited via radio frequency RF magnetron sputtering. The oxygen content in the sputtering process gas is systematically varied, revealing its critical role in influencing the films charge carrier density, mobility, and resistivity. Optimal conductivity resistivity as low as 3.4m amp; 937; cm is achieved at an argon oxygen mix gas flow rate of 3.4 sccm combined with quasi in situ heating, enhancing both charge carrier density and mobility. Optical analysis revealed that transmittance and absorptance depend on oxygen flow. In the long wavelength range, absorption scales with the number of free carriers, while in the short wavelength range, discrete absorption peaks below the band gap were observed, possibly originating from a secondary SnO like phas
Laboratory Based Soft X Ray Tomography A Novel Laser Design, Source Monitoring, and Data Processing Workflow
No full textMethod development for laboratory based X ray microscopes operating in the water window range invariably involves the development of the X ray source as well. This paper presents major upgrades to the laboratory soft X ray microscope L TXM plasma chamber and data analysis protocol. Characterization of the laser plasma source demonstrates improved performance, while a proof of principle tomogram of a diatom showcases a robust data treatment protocol and the system s capabilities for three dimensional imaging and segmentation. These developments mark significant progress toward making L TXM a more robust and user friendly tool for soft X ray microscopy application
Predicting Performance and Stability in Perovskite Photovoltaics by Quantifying Extraction and Recombination at Semiconductor Selective Contact Interfaces
No full textThe commercialization of perovskite photovoltaics relies on controlling the interfaces, where efficiency and stability are critically determined. These heterojunctions between the perovskite absorber and charge selective contacts represent non radiative recombination channels, which limit charge extraction and initiate long term degradation. However, their microscopic dynamics remain difficult to access, as most experimental probes average over the bulk or provide only indirect signals. This thesis develops a strategy to open this black box by uniting surface sensitive and optoelectronic characterization with drift diffusion DD modeling. The first study investigated TiO2 co doped with Nb V and Sn IV as an electron selective contact for CsPbI3. Kelvin probe force microscopy and time of flight secondary ion mass spectrometry showed that co doping increased bulk conductivity and suppressed interface trap states. A DD model was parameterized and quantitatively fitted to transient surface photovoltage trSPV data. The simulations revealed that co doping reduced the interface hole recombination velocity and increased the number of extracted electrons. These microscopic improvements translated into macroscopic improvements in open circuit voltage and fill factor, and extended device stability. The second study moved from materials optimization to a conceptual generalization. It addressed the apparent paradox that steady state photoluminescence PL is often quenched when device performance improves. Applying PL, trSPV, and DD modeling across three classes of semiconductor CSC heterojunctions showed that PL quenching can arise not from increased non radiative losses but from efficient charge extraction. The decisive parameter is the ratio of interface to bulk lifetimes amp; 964;interf amp; 964;bulk , which determines whether PL quenching or enhancement is observed. From this insight, a decision tree was derived that classifies interface quality from PL and trSPV alone, validated on more than 80 heterojunctions. These results demonstrate that buried interfaces can be understood and optimized through the combination of chemical modifications with predictive modeling. This thesis contributes both a concrete route to more efficient and stable perovskite photovoltaics and a generalizable methodology for distinguishing recombination from extraction at semiconductor interfaces. By establishing this link between microscopic interface physics and macroscopic device function, it points toward accelerated, rational design of photovoltaic technologie
Design, Synthesis, and Unprecedented Interactions of Covalent Dipeptide Based Inhibitors of SARS CoV 2 Main Protease and Its Variants Displaying Potent Antiviral Activity
No full textThe main protease Mpro of SARS CoV 2 is a key drug target for the development of antiviral therapeutics. Here, we designed and synthesized a series of small molecule peptidomimetics with various cysteine reactive electrophiles. Several compounds were identified as potent SARS CoV 2 Mpro inhibitors, including compounds 8n IC50 0.0752 amp; 956;M , 8p IC50 0.0887 amp; 956;M , 8r IC50 0.0199 amp; 956;M , 10a IC50 0.0376 amp; 956;M , 10c IC50 0.0177 amp; 956;M , and 10f IC50 0.0130 amp; 956;M . Most of them additionally inhibited cathepsin L and were also active against SARS CoV 1 and MERS CoV Mpro. In Calu 3 cells, several inhibitors, including 8r, 10a, and 10c, displayed high antiviral activity in the nanomolar range without showing cellular toxicity. The cocrystal structure of SARS CoV 2 Mpro in complex with 8p revealed covalent binding to the enzyme s catalytic residue Cys145 and showed specific, unprecedented interactions within the substrate binding pocket. Compounds 10c and especially 8n were effective against a panel of naturally occurring nirmatrelvir resistant mutants, particularly E166V, and showed metabolic stability and additional favorable pharmacokinetic properties, making it a suitable candidate for further preclinical developmen
Observation of Highly Spin Polarized Dangling Bond Surface States in Rare Earth Pnictide Tellurides
No full textTo generate and manipulate spin polarized electronic states in solids are crucial for modern spintronics. The textbook routes employ quantum well states or Shockley topological type surface states whose spin degeneracy is lifted by strong spin orbit coupling and inversion symmetry breaking at the surface interface. The resultant spin polarization is usually truncated because of the intertwining between multiple orbitals. Here a unique type of surface states is realized, namely, dangling bond surface states in a family of ternary rare earth pnictide tellurides RePnTe Re La, Gd, Ce; Pn Sb, Bi , with robust band structure and sizeable spin splitting. Spin and angle resolved photoemission spectroscopy measurements reveal high spin polarization and distinct spin momentum locking texture, which, according to the theoretical analysis, arise from local site asymmetry and surface purified spin orbital texture. The work extends the so called hidden spin polarization from the bulk to the surface, presenting an intriguing spin orbital momentum layer locking phenomenon, which may shed lights on potential spintronic application
Optimizing bimetallic NiRu Ti3C2Tx catalysts for oxygen evolution The Impact of MXene content on Ru stability
Get PDFIn this study, a bimetallic NiRu compound, synthesized by combining Ru with Ni and integrated it onto Ti3C2Tx MXene surfaces at varying MXene contents 1 25 using a facile hydrothermal method were investigated for the Oxygen Evolution Reaction OER . The NiRu Ti3C2Tx composites were evaluated in 1 M KOH electrolyte to assess how different MXene concentrations affect Ru stability and overall OER activity. Various characterization techniques were employed to analyze the morphological and microstructural properties of the synthesized pure and composite materials in order to elucidate the reasoning for the effect of the MXene on the Ru chemical stability and on the subsequent OER activity. We report that the incorporation of the bimetallic NiRu compound onto Ti3C2Tx MXene surfaces at varying MXene contents significantly hindered the Ru leaching by maintaining the Ru oxidation state during oxygen evolution. The synthesized NiRu MXene electrocatalysts demonstrated that MXenes can be utilized to stabilize the NiRu structure leading to less leaching of ionic and solid Ru species during the OER, while also delivering excellent OER activit
Water Electrooxidation Kinetics Clarified by Time Resolved X Ray Absorption and Electrochemical Impedance Spectroscopy for a Bulk Active Cobalt Material
No full textWater oxidation, the oxygen evolution reaction OER , is the anodic process in electrocatalytic production of hydrogen and further green fuels. Transition metal oxyhydroxides with bulk phase OER activity of the complete material or amorphized near surface regions are of prime application interest, but their basic electrochemical properties are insufficiently understood. Here the timescale of functional processes is clarified by time resolved X ray absorption spectroscopy and electrochemical impedance spectroscopy EIS for a thickness series of cobalt oxyhydroxides films about 35 550 nm . At the outer material surface, an electric double layer is formed in microseconds followed by clearly cobalt centered redox state changes of the bulk material in the low millisecond domain and a slow chemical step of O2 formation, within hundreds of milliseconds. Conceptually interesting, the electrode potential likely controls the OER rate indirectly by driving the catalyst material to an increasingly oxidized state which promotes the rate limiting chemical step. Rate constants are derived for redox chemistry and catalysis from EIS data of low thickness catalyst films; at higher thicknesses, catalyst internal charge transport limitations become increasingly relevant. Relations between electrochemically active surface area, double layer capacitance, and redox pseudo capacitance are discussed. These results can increase the power of EIS analyses and support knowledge guided optimization of a broader class of OER catalyst material
Visualizing the Future Recent Progress and Challenges on Advanced Imaging Characterization for All Solid State Batteries
Get PDFAll solid state batteries ASSBs offer high safety and energy density, but their degradation and failure mechanisms remain poorly understood due to the buried interfaces within solid state electrodes and electrolytes. Local probing methods are crucial for addressing key challenges such as interfacial instabilities, dendrite growth, and chemo mechanical degradation. State of the art imaging techniques provide critical insights into morphological, structural, and compositional evolution of the ubiquitous interfaces in ASSBs. This review highlights recent progress in cutting edge visualization techniques, including neutron imaging, X ray tomography, focused ion beam scanning electron microscopy, and cryogenic electron microscopy, which reveal microstructural and chemical changes in ASSBs at scales from the atomic to the macroscopic level. We particularly focus on the elusive failure behaviors at lithium anodes, composite cathodes, solid state electrolytes, and beyond. Additionally, we discuss the strengths and limitations of each technique, aiming to enhance the understanding of ASSB operation and degradation mechanisms to advance the development of high energy density, high safety ASSB
Accelerated ultrafast demagnetization of an interlayer exchange coupled Co Mn Co trilayer
Get PDFWe investigate the ultrafast magnetization dynamics of an interlayer exchange coupled Co Mn Co trilayer system after excitation with an ultrafast optical pump. We probe element and time resolved ferromagnetic order by x ray magnetic circular dichroism in resonant reflectivity. We observe an accelerated Co demagnetization time in the case of weak total parallel interlayer coupling at 9.5 ML Mn thickness for antiparallel alignment of both Co layers compared to parallel alignment as well as for parallel alignment in the case of strong parallel interlayer coupling at 11 ML of Mn. From ab initio time dependent density functional theory calculations, we conclude that optically induced intersite spin transfer of spin polarized electrons from Co into Mn acts as a decay channel to enhance and accelerate ultrafast demagnetization. This spin transfer can only take place in case of a collinear Mn spin structure. We argue that this is the case for antiparallel alignment of both Co layers at 9.5 ML Mn thickness and parallel alignment in case of 11 ML of Mn. Our results point out that an antiferromagnetic spacer layer and its spin structure have a significant effect on the magnetization dynamics of adjacent ferromagnetic layers. Our findings provide further insight into fundamental mechanisms of ultrafast demagnetization and may lead to improve dynamics in multilayered systems for faster optical switching of magnetic orde