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Interfacial Reactions Between Atomic Layer Deposited NiOx Hole Transport Layers and Metal Halide Perovskites in n i p Perovskite Solar Cells
Full text linkThe hole transport layer HTL plays a critical role for the stability and efficiency of perovskite solar cells PSCs as it forms a direct interface with the metal halide perovskite MHP and contact electrode. In the widely researched n i p architecture PSCs, organic HTLs like p doped spiro OMeTAD 2,2 amp; 8242;,7,7 amp; 8242; tetrakis[N,N di 4 methoxyphenyl amino] 9,9 amp; 8242; spirobifluorene and PTAA poly [bis 4 phenyl 2,4,6 trimethylphenyl amine] are commonly used to fabricate high efficiency devices. Despite the high efficiency, the inherent instability and hygroscopic nature of these doped organic HTLs are of major concern for the stability of PSCs. In this work, we incorporated atomic layer deposition ALD based nickel oxide NiOx HTLs into n i p PSCs, which serve the function of effective charge selective transport and pre encapsulation layers and investigated its interface formation with the MHP using synchrotron based hard X ray photoelectron spectroscopy. Our study reveals that the ALD NiOx film grown on the MHP contained a high concentration of hydroxide and oxy hydroxide species. Additionally, defect species, including nitrogen and lead based compounds, formed in the perovskite layer at the interface, which adversely affected PSC performance. To mitigate undesirable chemical reactions that occur during the ALD process, we introduced a 20 nm PTAA interlayer as a buffer between the MHP and ALD NiOx layers. This resulted in improved device efficiency and enhanced operational stabilit
Unlocking the Potential of Cobalt Free Lithium Ion Cathodes via Lithium Rich Disorder Domains
No full textHigh voltage, low nickel, cobalt free layered oxides are promising candidates for high energy density lithium ion batteries. However, their practical application is hindered by intrinsic cation disorder and structural degradation at high voltages, leading to a poor electrochemical performance. Here, we report a slightly lithium enriched, cobalt free layered oxide, Li1.05Ni0.43Mn0.52O2, featuring lithium rich disorder domains achieved through chemical composition optimization. Advanced structural characterization demonstrates that nickel ions not only reside within the TM layers but also occupy the Li layers, acting as pinned ions. Theoretical calculations indicate that this in plane and out of plane disorder enables reversible oxygen redox activity without oxygen release at high voltages. Moreover, this local structural framework preserves integrity even after extended cycling, ensuring chemical and structural stability during battery operation. Consequently, the cathode delivers an impressive discharge capacity of 202.2 mAh g 1 at C 10 and exceptional cycling stability, retaining 96.3 of its capacity after 200 cycles at C 3 within a voltage range of 2.5 4.55 V. Our findings provide valuable insights into the design of high energy density, cobalt free layered cathode
Polaronic Quasiparticles in the Valence Transition Compound TmSe1 xTex
No full textExotic quasiparticle states have been proposed in mixed valent compounds exhibiting valence transitions. However, clear spectroscopic evidence identifying these states has remained elusive. Using synchrotron based hard x ray and extreme ultraviolet photoemission spectroscopy, we have probed the Tm 3 amp; 8290; amp; 119889; and 4 amp; 8290; amp; 119891; emissions in TmSe1 amp; 8722; amp; 119909; amp; 8290;Te amp; 119909;, where a Te concentration dependent semimetal insulator transition occurs alongside the valence transition. Our photoemission results, which are characteristic of the bulk, track this combined transition across the critical concentration amp; 119909; amp; 119888; 0.29 . Notably, our results reveal a noninteger valence for the insulating phase and a novel quasiparticle excitation in the semimetallic phase a Holstein polaron that extends beyond the standard periodic Anderson mode
Monolayers of Thiols with Very High Dipole Moments Show Surprisingly Small Work Function Changes
No full textA recently introduced concept of distributed dipoles in molecular self assembly was combined with the standard dipolar tail group decoration in the context of the electrostatic engineering of surfaces and interfaces by self assembled monolayers SAMs . To this end, thiol anchored molecules, containing dipolar 2,5 amp; 8242; bipyrimidine units within their molecular backbones, were decorated with either nitrile or dimethylamino tail groups and assembled on Au 111 . The directions of the distributed and tail group dipoles were aligned either upward or downward to the anchor to achieve the maximum effect on the work function WF of the substrate. The SAMs were characterized by several complementary spectroscopic tools, with the data suggesting a dense molecular packing, a high degree of orientational order with only slight molecular inclination, and thiolate gold anchoring for most of the molecules. At the same time, it turned out that the decoration of the bipyrimidine thiols with the tail groups not only provided no WF gain but even had a detrimental effect in the dimethylamino case. The most likely explanation for this outcome, based on the analysis of the available data, is the upside down orientation of a part of the molecules in the SAMs, corresponding to their flip by 180 with respect to the standard thiolate anchoring configuration. The driving force of such a flip is the minimization of the energy associated with the strong dipole dipole interaction between the SAM forming molecules. Although being negative, this result can help in further rational design of functional molecules for WF adjustment, which is an important issue in organic electronics and photovoltaic
Sequentially Evaporated Wide Bandgap Perovskite Absorber for Large Area and Reproducible Fabrication of Solar Cells
Full text linkHerein, we perform sequential deposition of the organic and inorganic sub components evaporated from point sources, followed by thermal conversion to yield wide bandgap perovskite films for the application in perovskite silicon tandem cells. In our approach, uniform formamidinium iodide FAI layers with varying thicknesses are first deposited with rotating substrate. We next co evaporate the inorganic precursors PbI2, PbBr2, and CsI onto the FAI layer in a static mode, without substrate rotation, leading to thickness gradients across the substrate, known from single layer characterization. To promote conversion to amp; 945; phase perovskite, another uniform FAI layer is deposited on top, sandwiching the inorganic precursor layer stack. After thermal conversion, we obtain controlled compositional variations of the perovskite layer. Using spatially resolved characterization techniques, the most suitable composition, hence, evaporation rates for the individual inorganic precursors and the best thickness of the FAI sublayer are identified in a time efficient manner. As a result, an optimized average implied open circuit voltage, iVOC, of about 1230 mV and optical bandgap of 1.70 eV, very uniformly distributed over a half M6 wafer area, were achieved for the absorbers when deposited on a self assembled monolayer. Without any perovskite surface passivation or additional treatment, single junction devices with an average fill factor of 70 65 in reverse forward light current voltage scan and VOC of 1075 mV were achieved across several batches. Integrating this absorber in tandem cells with a random pyramid textured bottom cell led to preliminary cells with efficiencies up to 2
Technetium and Rhenium Auto reduction, Polymerization and Lability towards Group VII Polyoxometalate Chemistry
No full textGroup VII Tc and Re have long been studied to develop both radiopharmaceuticals and technologies for nuclear materials management. Fundamental research has targeted understanding this periodic table crossroads where polyoxometalates meets metal metal bonded complexes. Here we have isolated green hygroscopic and metastable crystals of ReVI,oct 2 ReVII,tet 2 OH 2 O 12 amp; 8901;H2O ReVI,VII green, tet tetrahedral, oct octahedral , determined by single crystal x ray diffraction. In addition to color, Re L1 X ray absorption near edge spectroscopy confirms the reduced oxidation state. ReVI,VII green provides the first demonstration of Re autoreduction, long observed for Mn and Tc. We also isolated and structurally characterized [Tc4O4 H2O 2 ReO4 14]2 amp; 8722; Tc4Re14 polyanion crystals that contain Tc V and Re VII , consistent with greater stability of reduced Tc compared to reduced Re. Small angle X ray scattering of both compounds and prior reported polyanion [Tc4O4 H2O 2 TcO4 14]4 amp; 8722; Tc20 dissolved in acetonitrile indicated a qualitative lability order of oxo linkages of Re O amp; 8722;Re gt; Re O amp; 8722;Tc gt;Tc O amp; 8722;Tc, and lability of Tc20 was also probed by 99Tc nuclear magnetic resonance spectroscopy. Computation provided insight into 99Tc chemical shifts as well as lability. Based on both reducibility and solution phase dynamics of polynuclear compounds investigated here, Re is an imperfect surrogate for Tc, and further expansion of group VII polyoxometalate chemistry seems promisin
Urea synthesis by Plasmon Assisted N2 and CO2 co electrolysis onto heterojunctions decorated with silver nanoparticles
No full textThe N2 CO2 co electrolysis to urea synthesis has become a promising alternative to the energy intensive traditional processes for urea production. However, there are still challenges in this approach, especially due to the competition with HER Hydrogen Evolution Reaction leading to low efficiency. Electrochemistry assisted by localized surface plasmon resonance LSPR using metal nanoparticles has been reported to enhance different electrochemical reactions. Here we report an electrochemical LSPR assisted urea synthesis using Ag nanoparticles NPs supported on BiVO4 BiFeO3 catalyst mechanochemically synthesized. The electrochemical experiments were performed under dark and upon plasmon excitation at the LSPR region of Ag NPs. Our results demonstrated that exciting in the LSPR range, urea yield rate and Faradic efficiency were considerably improved with reduced overpotential, 19.2 amp; 956;mol h amp; 8722;1 g amp; 8722;1 and FE 24.4 at 0.1 V vs RHE compared to 9.6 amp; 956;mol h amp; 8722;1 g amp; 8722;1 and FE 9.4 at amp; 8722;0.2 V vs RHE under dark conditions. Further in situ FTIR RAS experiments for mechanism investigation revealed the presence of N H and C N intermediates and the real effect of Ag plasmon excitation on HER and N2 CO2 co electrolysis. Theoretical calculations confirm the energy of the species involved in C N coupling as well the role of the complex catalytic sites, which agrees with XAS measurement
Formation, Phase Transition, Surface, and Catalytic Properties of Cubic ZrO2 Nanocrystals
No full textZrO2 is a relevant industrial and technological material with structure dependent properties. The high temperature tetragonal and cubic phases can be stabilized at room temperature through the incorporation of stabilizing cations. Tetragonal pure ZrO2 can additionally be stabilized by reducing the crystallite size to the nanoscale; however, stabilizing cubic pure ZrO2 at room temperature remains challenging. Here, cubic ZrO2 nanocrystals are synthesized by reacting a low concentration of ZrCl4 0.025 mol L 1 with acetophenone. Pair distribution function and extended X ray absorption fine structure analyses reveal that the local structure around the zirconium atoms is highly distorted relative to that of the ideal cubic. The structure can be modified by increasing the precursor concentration up to 0.1 mol L 1 , eventually leading to the formation of entirely monoclinic nanocrystals. The surface properties and catalytic behavior of cubic ZrO2 are investigated for establishing structure property correlations and comparisons with the monoclinic phase. An optimized combination of activity, product yields, and recyclability in the multistep conversion of amp; 945; angelica lactone to amp; 947; valerolactone is achieved with small cubic ZrO2 particles of 2.3 0.4 nm size. Our results provide insights into the stabilization of cubic ZrO2 and phase transitions at room temperature and demonstrate the potential of cubic type pure ZrO2 for catalytic application
A Spectroscopic Criterion for Identifying the Degree of Ground Level Near Degeneracy Derived from Effective Hamiltonian Analyses of Three Coordinate Iron Complexes
Full text linkThe fascinating magnetic and catalytic properties of coordinatively unsaturated 3d metal complexes are a manifestation of their electronic structures, in particular their nearly doubly or triply degenerate orbital ground levels. Here, we propose a criterion to determine the degree of degeneracy of this class of complexes based on their experimentally accessible magnetic anisotropy parametrized by the electron spin g and zero field splitting ZFS tensors . The criterion is derived from a comprehensive spectroscopic and theoretical study in the trigonal planar iron 0 complex, [ IMes Fe dvtms ] IMes 1,3 di 2 amp; 8242;,4 amp; 8242;,6 amp; 8242; trimethylphenyl imidazol 2 ylidene, dvtms divinyltetramethyldisiloxane, 1 . Accurate ZFS values D 33.54 cm 1, E D 0.09 and g values g amp; 8741; 1.96, g amp; 8869; 2.45 of the triplet S 1 ground level of complex 1 were determined by complementary THz EPR spectroscopy and SQUID magnetometry. In depth effective Hamiltonian EH analyses coupled to wave function based ab initio calculations show that 1 features a ground level with three energetically close lying orbital states with a two above one energy pattern. The observed magnetic anisotropy results from mixing of the two excited electronic states with the ground state by spin orbit coupling SOC . EH investigations on 1 and related complexes allowed us to generalize this finding and establish the anisotropy of the g and ZFS tensors as spectroscopic markers for assigning two or three fold orbital near degenerac
PM magnet development status for BESSYII
Full text linkBeam guiding magnets based on permanent magnets PM combine up to zero power consumption with highly stable magnet operation without field ripple and cooling water vibration effects for more energy efficient and stable accelerator operation. As part of the upgrade program BESSYII , we will install the B2PT dipole triplet as the first PM based accelerator magnet. It concludes the BESSYII transfer line, transporting the electron beam from the booster to the storage ring and bends the beam into the injection septum of the BESSYII storage ring. The new B2PT is planned with three PM hybrid dipole units of 300 mm length each to substitute the present power hungry 1 m long electromagnet. The triplet produces a stable magnetic field that can be trimmed during operation by electro correctors in the outer magnets. The permanent magnetic field reduces injection noise into the storage ring and shrinks the total power consumption by almost 30 kW. This paper reviews simulated beam bending optimization of the B2PT PM triplet and its assembly process opening up to PM magnet development also required for the preparation of the future 4th generation low emittance source BESSYII