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Results for “Optical Absorption”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Density functional theory investigation of the LiIn 1- x Ga x Se 2 solid solution

Here, the electronic structure and optical properties of the LiIn 1-x Ga x Se 2 (x=0, 0.25, 0.5, 0.75, 1) solid solution were studied by density functional theory (DFT) with pure functionals. The exchange-correlation is treated within the local density approximation (LDA) and generalized-gradient approximation (GGA). The electronic structures for each respective compound are discussed in detail. Calculations reveal that gallium incorporation can be used to tune the optical-electrical properties of the solid solution and correlates with the lattice parameter. The band gap trend of the LiIn 1-x Ga x Se 2 system follows a nonlinear behavior between the LiInSe 2 and LiGaSe 2 ternary boundaries. The bowing parameter is estimated to be on the order of 0.1- 0.3 eV at the point. Low-temperature optical absorption revealed a 30% change in the temperature dependence of the band gap for the intermediate compound LiIn 0.6 Ga 0.4 Se 2 compared to ternary boundaries and suggests the heat capacity to be another control element through strain.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Laser‐Sintered Silver Metallization for Silicon Heterojunction Photovoltaic Cells

Herein, a novel metallization technique is reported for crystalline silicon heterojunction (SHJ) solar cells in which silver (Ag) fingers are printed on the SHJ substrates by dispensing Ag nanoparticle‐based inks through a needle and then sintered with a continuous‐wave carbon dioxide (CO 2 ) laser. The impact of the Ag ink viscosity on the line quality and the line resistance is investigated on three Ag inks with different viscosities. Increasing ink viscosity yields higher Ag contact heights, larger aspect ratios, and lower line resistance values. The Ag line height increases from less than a micrometer to ≈18.62 ± 3.48 μm with the increasing viscosity. Photoluminescence imaging shows that the low‐resistance Ag metal contacts obtained do not result in any passivation damage of the SHJ substrate. This is because the wavelength of light emitted from the CO 2 laser (i.e., 10.6 μm) leads to optical absorption in the Ag, but this light is effectively transparent to the transparent conductive oxide film, amorphous silicon films, and crystalline silicon substrate. Bulk resistivity values as low as 6.5 μΩ cm are obtained for the laser‐sintered Ag contact and printed using the Ag ink with the highest viscosity in this work.

Mousumi, Jannatul Ferdous↗
DOE OSTI2017

Uranium Oxide Nanocrystals by Microwave-Assisted Thermal Decomposition: Electronic and Structural Properties

Uranium oxides have attracted much attention not only in the context of nuclear energy generation but also for their application as pristine catalysts or as supports for other (transition metal) oxides and (precious) metals. Their propensity to adopt high coordination numbers and manifest multiple oxidation states (from +II to +VI) makes them attractive candidates for catalyzed transformation reactions. In this paper, we report a new synthesis route to phase-pure, crystalline UO 2 nanoparticles via microwave-assisted decomposition of a molecular uranium(IV) precursor. Finally, the electronic structure and optical absorption properties of these nanocrystals were investigated using spectroscopic methods to evaluate their suitability for photo(electro)catalytic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

First-Principles Study of Pressure Dependence of Optical Spectra of MnS

MnS is a semiconductor material that can be used in solar cell coatings as window/buffer material and in many other applications. The present contribution deals with the optical properties of MnS in the zinc-blende structure using ab initio calculations within the generalized gradient approximation. Features such as dielectric function, refractive index, reflectivity, optical absorption, conductivity, and electron loss function spectra have been reported and their pressure dependence has been examined and discussed. The information gathered from the present study can be useful for photovoltaic applications.

14 SOLAR ENERGY↗
DOE OSTI2019

Fabrication of Graphene-Supported Palladium Nanoparticles-Decorated Zinc Oxide Nanorods for Potential Application

We report the facile synthesis of graphene-supported palladium (Pd) nanoparticles anchored zinc oxide nanorods (Pd-ZnO/G) by the sol-gel method. X-ray diffraction (XRD) pattern confirmed the hexagonal wurtzite crystal structure (with P6{sub 3}mc phase) of Pd-ZnO/G nanorods similar to ZnO structure. X-ray diffraction results showed that graphene-supported Pd nanoparticles anchored on ZnO nanorods increases the average crystallite size of ZnO nanorods. Field emission scanning electron microscopy (FESEM) revealed the successful anchoring of Pd nanoparticles on the surface of ZnO/G nanorods. X-ray spectroscopy (XPS) was used to obtain the different oxidation state and surface compositional details of nanorods. Energy dispersive spectroscopy analysis confirmed the presence of palladium, carbon, and oxygen in Pd-ZnO/G structure. The optical absorption measurement indicates that after graphene and palladium doping, it shifted towards the low wavelength region for Pd-ZnO/G structure and high wavelength region in the case of ZnO/G nanostructure. Magnetic measurement showed that the saturation magnetization of Pd nanoparticles anchored nanorods increased when compared with that of ZnO/G and ZnO nanorods.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Design and analysis of graphene–MoS{sub 2} hybrid layer based SPR biosensor with TiO{sub 2}–SiO{sub 2} nano film for formalin detection: numerical approach

In this paper, a Surface Plasmon Resonance (SPR) biosensor has been numerically developed that used Graphene–MoS{sub 2}–Au–TiO{sub 2}–SiO{sub 2} hybrid structure for the detection of formalin. This developed sensor has been sensed the presence the formalin based on attenuated total reflection (ATR) method by observing the change of “surface plasmon resonance angle-the change of minimum reflectance attributor” and “the resonance frequency characteristics (RFC)-maximum transmittance attributor”. Chitosan has been used as probe sensing medium to accelerate particular reaction with the formalin. Here, graphene is used as biomolecular recognition element because of its high adsorption ability and optical characteristics which helps to improve sensor sensitivity, MoS{sub 2} used for it has larger band gap, high fluroscence quenching ability, higher optical absorption efficiency, TiO{sub 2}–SiO{sub 2} bilayer as the improvement of sensitivity and Gold (Au) as the sharp SPR curve. Numerical results give the impression that the variation of RFC and SPR angle for improper sensing of formalin is quiet negligible that confirms no formalin is detected whereas for proper sensing these change are considerably countable that confirms the detection of formalin. From the sensor sensitivity analysis, owing to add TiO{sub 2}–SiO{sub 2} bilayer with Graphene–MoS{sub 2} Hybrid layer, maximum sensitivity of 85.375% has been numerically resulted. This high sensor performance is for taking advantages of Graphene surface high selectively which detect bio molecular compounds through pi-stacking force, larger work function (5.1 eV) of MoS{sub 2} which allows the high sensitive detection of bio targets and Rich plasmon happens at the TiO{sub 2}–SiO{sub 2} interface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Optical and Electrical Properties of Sn-Doped Zinc Oxide Single Crystals

Here, Sn dopant in ZnO may significantly improve the n-type conductivity of ZnO through a characteristic double effect. However, studies on bulk Sn-doped ZnO are rare, and the effect of Sn doping on the optoelectronic properties of bulk ZnO is not well understood. In this work, the effect of Sn doping on the optical and electrical properties of ZnO bulk single crystals was investigated through optical absorption spectroscopy, Hall-effect measurements, and thermoluminescence (TL) spectroscopy. Undoped and Sn-doped ZnO single crystals were grown by chemical vapor transport method and characterized by x-ray diffraction analysis. The Sn doping level in the crystals was evaluated by inductively coupled plasma mass spectroscopy measurements. Hall-effect measurements revealed an increase in conductivity and carrier concentration with increasing Sn doping, while TL measurements identified a few donor species in the crystals with donor ionization energy ranging from 35 meV to 118 meV. Increasing Sn doping was also associated with a color change of single crystals from colorless to dark blue.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Possibility to Use Hydrothermally Synthesized CuFeS{sub 2} Nanocomposite as an Acceptor in Hybrid Solar Cell

Here we have approached the plausible use of CuFeS{sub 2} nanocomposite as an acceptor in organic–inorganic hybrid solar cell. To produce CuFeS{sub 2} nanocomposite, hydrothermal strategy was employed. The room-temperature XRD pattern approves the synthesized material as CuFeS{sub 2} with no phase impurity (JCPDS Card no: 37-0471). The elemental composition of the material was analyzed from the TEM-EDX data. The obtained selected area electron diffraction (SAED) planes harmonized with the XRD pattern of the synthesized product. Optical band gap (4.14 eV) of the composite from UV–Vis analysis depicts that the synthesized material is belonging to wide band gap semiconductor family. The HOMO (− 6.97 eV) and LUMO (− 2.93 eV) positions from electrochemical study reveal that there is a possibility of electron transfer from MEH-PPV to CuFeS{sub 2}. The optical absorption and photoluminescence spectra of MEH-PPV:CuFeS{sub 2} (donor:acceptor) composite were recorded sequentially by varying weight ratios. The monotonic blue shifting of the absorption peak position indicated the interaction between donor and acceptor materials. The possibility of electron transfer from donor (MEH-PPV) to acceptor (CuFeS{sub 2}) was approved with photoluminescence analysis. Subsequently, we have fabricated a hybrid solar cell by incorporating CuFeS{sub 2} nanocomposite with MEH-PPV in open atmosphere and obtained 0.3% power conversion efficiency.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Studies on optical properties of Si220 nanoclusters via time-dependent density functional theory calculations

The optical properties of bare and hydrogen passivated Si220 nanoclusters(NCs) in four typical motifs(i.e., bulk-like, onion-like, bucky-diamond and icosahedral motifs) were studied via time-dependent density functional theory(TD-DFT) calculations. The calculation results show that there is a significant blue shift in the optical absorption spectra when the Si NCs are passivated with hydrogen. A strong absorption peak in the visible light region appears for the hydrogenated bulk-like, onion-like and bucky-diamond Si NCs.

Yang, Wenhua↗
DOE OSTI2019

Theoretical study on optical response in nanostructures in the Born–Markov regime: The role of spontaneous emission and dephasing

We theoretically study the linear and nonlinear optical susceptibility in a nanostructure that interacts with a classical monochromatic optical field, by means of the solution of a Born–Markov master equation in the Lindblad form, considering as environment for the system the quantum vacuum of the continuum of modes of the external electromagnetic field. The processes of spontaneous emission and dephasing between two levels of the nanostructured quantum system are studied formally, within the framework of the quantum theory of open systems. It was found that the phenomenological master equation corresponds to a Born–Markov master equation in the Lindblad form that considers only the dissipative terms of spontaneous emission and dephasing, provided that the transverse coherence time T{sub 2} is smaller than spontaneous emission time T{sub 1}. Finally, comparative results are presented between the proposed methodology and the conventional method for: optical rectification, optical absorption, generation of second harmonic and generation of third harmonic in a cylindrical quantum dot (CQD) of AsGa∕AsGaAl with a hydrogen-like impurity inside it and under the action of a uniform magnetic field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Siloxane-functional small molecule acceptor for high-performance organic solar cells with 16.6% efficiency

As one of the simple but most effective molecular design strategies, side-chain engineering has been widely employed to modify the photoelectric properties of active layer materials for boosting the photovoltaic performance of organic solar cells (OSCs). In this work, a functionalized small molecule acceptor (SMA) named BTSi-4F with a bulky siloxane-terminated solubilizing group as side-chains, derived from a classical SMA of Y6, was designed and synthesized. The results demonstrate that the introduction of siloxane-functional terminated groups into SMA not only affects the optical absorption and molecular energy levels, but also regulates the miscibility between the polymer donor and SMA. Compared to the original Y6, BTSi-4F exhibits a better solubility, upshifted lowest unoccupied molecular orbital (LUMO) energy level, more ordered molecular packing, and higher electron-mobility. Matched with a wide bandgap polymer donor PM6, the chlorobenzene-processed OSCs based on PM6:BTSi-4F achieved a superior power conversion efficiency (PCE) of 16.6% with both high open-circuit voltage (V oc ) of 0.90 V and high fill factor (FF) of 0.77, while the devices based on PM6:Y6 obtained a much lower PCE of 13.0% with a V oc of 0.81 V and FF of 0.69 under the same conditions. This work offers a promising molecular design strategy of siloxane-terminated side chain engineering to develop high-performance SMAs for efficient OSCs.

14 SOLAR ENERGY↗
DOE OSTI2016

molgw 1: Many-body perturbation theory software for atoms, molecules, and clusters

Here, we summarize the MOLGW code that implements density-functional theory and many-body perturbation theory in a Gaussian basis set. The code is dedicated to the calculation of the many-body self-energy within the GW approximation and the solution of the Bethe–Salpeter equation. These two types of calculations allow the user to evaluate physical quantities that can be compared to spectroscopic experiments. Quasiparticle energies, obtained through the calculation of the GW self-energy, can be compared to photoemission or transport experiments, and neutral excitation energies and oscillator strengths, obtained via solution of the Bethe–Salpeter equation, are measurable by optical absorption. The implementation choices outlined here have aimed at the accuracy and robustness of calculated quantities with respect to measurements. Furthermore, the algorithms implemented in MOLGW allow users to consider molecules or clusters containing up to 100 atoms with rather accurate basis sets, and to choose whether or not to apply the resolution-of-the-identity approximation. Finally, we demonstrate the parallelization efficacy of the MOLGW code over several hundreds of processors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

QRCODE: Massively parallelized real-time time-dependent density functional theory for periodic systems

We present a new software module, QRCODE (Quantum Research for Calculating Optically Driven Excitations), for massively parallelized real-time time-dependent density functional theory (RT-TDDFT) calculations of periodic systems in the open-source Qbox software package. Our approach utilizes a custom implementation of a fast Fourier transformation scheme that significantly reduces inter-node message passing interface (MPI) communication of the major computational kernel and shows impressive scaling up to 16,344 CPU cores. In addition to improving computational performance, QRCODE contains a suite of various time propagators for accurate RT-TDDFT calculations. As benchmark applications of QRCODE, we calculate the current density and optical absorption spectra of hexagonal boron nitride (h-BN) and photo-driven reaction dynamics of the ozone-oxygen reaction. We also calculate the second and higher harmonic generation of monolayer and multi-layer boron nitride structures as examples of large material systems. Our optimized implementation of RT-TDDFT in QRCODE enables large-scale calculations of real-time electron dynamics of chemical and material systems with enhanced computational performance and impressive scaling across several thousand CPU cores.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Low temperature perovskite solar cells with an evaporated TiO 2 compact layer for perovskite silicon tandem solar cells

Silicon-based tandem solar cells can overcome the efficiency limit of single junction silicon solar cells. Perovskite solar cells are particularly promising as a top cell in monolithic tandem devices due to their rapid development towards high efficiencies, a tunable band gap with a sharp optical absorption edge and a simple production process. In monolithic tandem devices, the perovskite solar cell is deposited directly on the silicon cell, requiring low-temperature processes (< 200 °C) to maintain functionality of under-lying layers of the silicon cell in case of highly efficient silicon hetero-junction (SHJ) bottom solar cell. In this work, we present a complete low-temperature process for perovskite solar cells including a mesoporous titanium oxide (TiO 2 ) scaffold - a structure yielding the highest efficiencies for single-junction perovskite solar cells. We show that evaporation of the compact TiO 2 hole blocking layer and ultra-violet (UV) curing for the mesoporous TiO 2 layer allows for good performance, comparable to high-temperature (> 500 °C) processes. With both manufacturing routes, we obtain short-circuit current densities (J SC ) of about 20 mA/cm 2 , open-circuit voltages (V OC ) over 1 V, fill factors (FF) between 0.7 and 0.8 and efficiencies (n) of more than 15%. We further show that the evaporated TiO 2 layer is suitable for the application in tandem devices. The series resistance of the layer itself and the contact resistance to an indium doped tin oxide (ITO) interconnection layer between the two sub-cells are low. Additionally, the low parasitic absorption for wavelengths above the perovskite band gap allow a higher absorption in the silicon bottom solar cell, which is essential to achieve high tandem efficiencies.

14 SOLAR ENERGY↗
DOE OSTI2018

Probing ligand removal and ordering at quantum dot surfaces using vibrational sum frequency generation spectroscopy

Controlling nanomaterial interfaces for emerging technologies has driven the need to understand the molecular species located there; however, challenges arise using traditional analytical techniques to directly characterize the molecular structure and local environments of these interfacial species due to their low relative populations. We hypothesized that vibrational sum frequency generation (vSFG) spectroscopy would be uniquely sensitive to the chemical modification of nanoparticle surfaces that is obscured using traditional bulk sensitive methods. Octadecylamine ligands were removed from model CdSe quantum dot surfaces using a common precipitation-resuspension procedure with polar protic and aprotic nonsolvents. Vibrational spectra of the ligands at the surface were collected with vSFG to directly probe the ligand ordering and coverage. Photoluminescence (PL), optical absorption, NMR, and mass spectrometry measurements were conducted for comparison. vSFG was found to be sensitive to subtle changes in ligand disorder over multiple precipitation-resuspension washes, and a limit to the number of ligand molecules removed from the surface and subsequent amount of disorder introduced to their packing was clearly observed. As a result, we also find that nonsolvents do not remain associated with the surface after washing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Highly transparent ammonothermal bulk GaN substrates

A novel apparatus has been employed to grow ammonothermal (0001) gallium nitride (GaN) with diameters up to 2 in The crystals have been characterized by x-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), and optical spectroscopy. High crystallinity GaN with FWHM values about 20-50 arcsec and dislocation densities below 1 x 10(5) cm(-2) have been obtained. High optical transmission was achieved with an optical absorption coefficient below 1 cm(-1) at a wavelength of 450 nm. (C) 2014 Elsevier B.V. All rights reserved.

Jiang, WK↗
DOE OSTI2022

π-Extension and chlorination of non-fullerene acceptors enable more readily processable and sustainable high-performance organic solar cells

Organic solar cells (OSCs) processed without halogenated solvents and complex treatments are essential for future commercialization. Herein, we report three novel small molecule acceptors (NFAs) consisting of a Y6-like core but with π-extended naphthalene with progressively more chlorinated end-capping groups and a longer branched chain on the Nitrogen atom. These NFAs exhibit good solubilities in non-chlorinated organic solvents, broad optical absorptions, close π-π stacking distances (3.63–3.84 Å), and high electron mobilities (~10 -3 cm 2 V -1 s -1 ). Further, the o-xylene processed and as-cast binary devices using PM6 as the donor polymer exhibit a PCE increasing upon progressive chlorination of the naphthalene end-capping group from 8.93% for YN to 14.38% for YN-Cl to 15.00% for YN-2Cl. Furthermore similarly processed ternary OSCs were fabricated by employing YN-Cl and YN-2Cl as the third component of PM6:CH1007 blends (PCE = 15.75%). Compared to all binary devices, the ternary PM6:CH1007:YN-Cl (1:1:0.2) and PM6:CH1007:YN-2Cl (1:1:0.2) cells exhibit significantly improved PCEs of 16.49% and 15.88%, respectively, which are among the highest values reported to date for non-halogenated solvent processed OSCs without using any additives and blend post-deposition treatments.

14 SOLAR ENERGY↗