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Highly Emissive Hexa peri benzocoronene fluoranthene Hybrid as Easily Processable and Stable OLED Material
Get PDFBernal Stacked Bilayer Graphene on Rh 111 Clear Evidence from ARPES and DFT
No full textThe growth and electronic structure of bilayer graphene gr on different substrates have attracted a lot of attention in the last years owing to the possibility of tuning the band gap in the electronic spectrum for the graphene amp; 960; states around the K point. In the present study, the electronic structure of single and double layer graphene on Rh 111 is studied using different surface science methods accompanied by DFT calculations. It is shown that in the case of 1 ML gr Rh 111 , the freestanding like electronic structure of graphene is completely destroyed due to the strong interaction with the metallic substrate. For the 2 ML gr Rh 111 system, the AB Bernal stacking of graphene layers is found, leading to the restoration of the electronic structure for the top graphene layer, its n doping, and opening of the band gap at the K point. These results lead to a deep understanding of the interaction mechanisms between multilayer graphene and metallic supports that can be used for better modeling of different graphene based application
Point contacts in halide perovskite solar cells from reduced interfacial recombination to increased ionic field screening
Get PDFThe performance of p i n structured perovskite solar cells PSCs is primarily limited by the charge recombination at the interface between the perovskite and the electron transporting layer, most commonly C60. Inspired by the silicon passivated emitter rear cell design, we propose point contacts PCs to reduce the recombination at the perovskite C60 interface. Inserting PCs between the perovskite and C60 layers enables an increased efficiency from 18.9 to 20.0 , which mainly originates from the reduced non radiative recombination that leads to a higher open circuit voltage VOC from 1.16 to 1.21 V. Combining a lithium fluoride LiF layer beneath the PCs perovskite LiF PCs can further boost the VOC to 1.26 V, reaching 90 of the detailed balance limit. However, we find that PCs exacerbate the effect of mobile ions in PSCs, accelerating the degradation under operando conditions. Our results reveal that mobile ions accumulate at the PCs, triggering a faster degradation of the device. These observations are further supported by one and two dimensional drift diffusion simulations that confirm the accumulation of ions at the PCs. This work, therefore, highlights the importance of ion management for improved stability and points to a new degradation mechanism when a discontinuous insulating layer forms at the perovskite interface
Detection limits of calcium by EELS, TEM EDX and X ray absorption spectroscopy for biomineralization studies
No full textTo investigate the mechanisms of biomineral formation it is necessary to determine Ca concentrations in the vicinity of growing minerals at the highest spatial resolution. All techniques that use ionizing radiation will be limited by the onset of radiation damage. Limits to the minimum concentrations of Ca and minimum number of Ca atoms that can be detected are determined for EELS in TEM using the Ca L23 signal, and EDX in TEM using the Ca Ka line. A similar approach is used to set limits on what can be achieved via soft X ray absorption spectroscopy detecting the Ca L 23 features. Due to the large background, the lowest concentrations that can be detected via EELS are about 1 mM. Although the collection efficiency for EDX is inferior to that of EELS, the much lower background signal means that concentrations of about 0.05 mM could be detected, 20 times better than EELS. The spatial resolution of soft X ray absorption spectroscopy is much lower, about 20 nm, but since the Ca L 23 lines are at lower energies than the oxygen K edge that dominates the spectrum, the detection limits for Ca in an aqueous environment can be as low as 35 n
Correlation of Band Bending and Ionic Losses in 1.68 eV Wide Band Gap Perovskite Solar Cells
Get PDFPerovskite solar cells PSCs are promising for high efficiency tandem applications, but their long term stability, particularly due to ion migration, remains a challenge. Despite progress in stabilizing PSCs, they still fall short compared to mature technologies like silicon. This study explores how different piperazinium salt treatments using iodide, chloride, tosylate, and bistriflimide anions affect the energetics, carrier dynamics, and stability of 1.68 eV bandgap PSCs. Chloride based treatments achieved the highest power conversion efficiency 21.5 and open circuit voltage 1.28 V , correlating with stronger band bending and n type character at the surface. At the same time, they showed reduced long term stability due to increased ionic losses. Tosylate treated devices offered the best balance, retaining 96.4 efficiency after 1000 h ISOS LC 1I . These findings suggest that targeted surface treatments can enhance both efficiency and stability in PSC
Ferromagnetic Nickel as a Sustainable Reducing Agent for Tin Lead Mixed Perovskite in Single Junction and Tandem Solar Cells
Get PDFNarrow bandgap NBG Sn Pb mixed perovskite solar cells PSCs represent a promising solution for surpassing the radiative efficiency of single junction solar cells. The unique bandgap tunability of halide perovskites enables optimal tandem configurations of wide bandgap WBG and NBG subcells. However, these devices are limited by the susceptibility of Sn2 in the NBG bottom cell to being oxidized to Sn4 , creating detrimental Sn vacancies. Herein, a novel approach that replaces Sn particles with Ni particles is introduced as the reducing agent for Sn Pb mixed perovskite precursor solutions. The ferromagnetic properties of Ni enable simple magnetic filtration, eliminating the filtration issues associated with Sn particles. Ni particles can be reused up to five times without significantly affecting the PSC s performance. Additionally, Ni effectively mitigates the oxidation of Sn2 due to its low reduction potential amp; 8722;0.23 V , thereby enhancing device performance. Single junction Sn Pb mixed PSCs prepared using Ni achieve a power conversion efficiency PCE of 22.29 , retaining over 90 of their initial efficiency after 1250 h. Furthermore, Ni based all perovskite tandem solar cells combining 1.77 eV WBG top cells with 1.25 eV NBG bottom cells achieve a remarkable PCE of 28.13 . Thus, the proposed strategy can facilitate the commercialization of all perovskite tandem device
Ising superconductivity in the bulk incommensurate layered material PbS 1.13 TaS2
No full textExploiting the spin valley degree of freedom of electrons in materials is a promising avenue for energy efficient information storage and quantum computing. A key challenge in utilizing spin valley polarization is the realization of spin valley locking in bulk systems. Here we report a comprehensive study of the noncentrosymmetric bulk misfit compound PbS 1.13 amp; 8290; TaS2 , showing a strong spin valley locking. Our investigation reveals Ising superconductivity with a transition temperature of 3.14 K, closely matching that of a monolayer of TaS2. Notably, the absence of charge density wave signatures in transport measurements suggests that the PbS layers primarily act as spacers between the dichalcogenide monolayers. This is further supported by angle resolved photoemission spectroscopy ARPES , which shows negligible interlayer coupling, a lack of dispersion along the amp; 119896; amp; 8869; direction, and significant charge transfer from the PbS to the TaS2 layers. Spin resolved ARPES shows strong spin valley locking of the electronic bands. Muon spin rotation experiments conducted in the vortex phase reveal an isotropic superconducting gap. However, the temperature dependence of the upper critical field and low temperature specific heat measurements suggest the possibility of multigap superconductivity. These findings underscore the potential of misfit compounds as robust platforms for both realizing and utilizing spin valley locking in bulk materials, as well as exploring proximity effects in two dimensional structure
Sintering of inkjet printed silver nanoparticles by large area atmospheric pressure nitrogen plasma
Get PDFSilver nanoparticles were sintered at atmospheric pressure using nitrogen plasma generated by diffuse coplanar surface barrier discharge DCSBD . Compared to the standard thermal sintering of 1 h at 140 C only 8 min of nonthermal plasma treatment at 50 C were necessary to sufficiently anneal the silver nanoparticle film. Electrical resistivity as low as 9 amp; 8201; amp; 8201;10 6 amp; 937; cm was achieved, i.e., 17 of the bulk conductivity of silver. X ray photoelectron spectroscopy was used to study the removal of organic moieties from the surface of the inkjet printed layers. Scanning electron microscopy revealed in detail the process of formation of interconnection between nanoparticles. Our findings pave the way for implementing low cost and eco friendly DCSBD plasma sintering into continuous roll to roll processing in the future for the annealing of silver nanoparticles on substrates that cannot tolerate high temperature
Toward Understanding the Built in Field in Perovskite Solar Cells through Layer by Layer Surface Photovoltage Measurements
Get PDFThe built in voltage VBI is a key parameter for solar cell operation, yet in perovskite solar cells the distribution, magnitude, and origin of the VBI remains poorly understood. In this work, we systematically studied the VBI in pin type perovskite solar cells based on different hole transport layers TLs . To this end, we determine the surface photovoltage SPV of partial and complete device stacks layerby layer by measuring the work function WF under dark and light equivalent AM1.5G conditions with Kelvin probe KP and photoemission spectroscopy UPS measurements in 3 different laboratories. We demonstrate that the SPV increases upon the addition of each additional layer until it equals the open circuit voltage VOC of the full device. This suggests that both the electron and hole transport layer HTL ETL enlarge the SPV, by improving the separation of photogenerated carriers. Yet, the contribution of both transport layers to the total SPV of the device is small in the range of amp; 8776;100 to 200 meV and the largest contribution to the SPV originates from the top metal electrode amp; 8776;500 meV . The results suggest that the VBI of pin type perovskite solar cells is largely a result of the workfunction difference of the electrodes. With regard to films or incomplete cell stacks , our simulations can reproduce the measured SPV, and measured quasi Fermi level splitting gt;VOC in partial cell stacks without a significant internal field consistent with the experimental data. This work establishes layer by layer SPV measurements, which are easily accessible, as a key tool for understanding device performance and internal energetics, similar to layer by layer QFLS measurement
Complete 3D photoelectron momentum vector reconstruction from time position charged particle imaging
No full textMany charged particle imaging techniques exist which directly measure, at a detector, the transverse position x, y and time of flight t of individual events in order to obtain a full set of 3D coordinates. Where curved velocity mapping electric field lines are implemented, as in the case of 3D Velocity Map Imaging 3D VMI and certain COLTRIMS Cold Target Recoil Ion Momentum Spectroscopy instruments, the general transformation of x, y, t data into initial 3D recoil momentum vectors px, py, pz is challenging and has not yet been fully addressed. Here we present a detailed and general method for this transformation, illustrated using our 3D VMI spectrometer and the well known narrow band photoionization of nitric oxide, for which we demonstrate quantitative agreement with reported values. We additionally show how to measure and correct i small errors in the laser polarization axis alignment at the interaction region of a 3D charged particle imaging spectrometer, and ii the spatial variation of gain on a microchannel plate MCP detector. Improvements to and characterization of our 3D VMI spectrometer yield an electron time of flight resolution of 72 ps across the full 40 mm MCP, in combination with pixel level spatial resolutio