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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Enhanced Photoluminescence of Heavily Doped n-Ge/Si(001) Layers

The photoluminescence spectra of epitaxial n{sup +}-Ge:P/Si(001) structures are studied. The structures are grown by hot-wire chemical vapor deposition and doped with phosphorus to the maximum electron concentration 1 × 10{sup 20} cm{sup –3} from a source based on thermally decomposed GaP. The effects of the doping level and rapid thermal annealing of n{sup +}-Ge:P layers on the photoluminescence spectra are studied. It is demonstrated that the epitaxial n{sup +}-Ge:P/Si(001) layers grown by hot-wire chemical vapor deposition are promising for application as active regions of light-emitting optoelectronic devices operating in the near-infrared spectral region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Examination of the Capabilities of Metalorganic Vapor-Phase Epitaxy in Fabrication of Thin InAs/GaSb Layers

The capabilities of metalorganic vapor-phase epitaxy (MOVPE) in fabrication of structures with thin (1–2 nm) alternating InAs/GaSb layers on a GaSb substrate are studied. The characteristics of these structures were examined using transmission electron microscopy and methods of photo- and electroluminescence. It was found that two GaInAsSb solid solutions of different compositions were formed in the active regions of structures in the given growth conditions. The fabricated system was characterized by an emission wavelength of 4.96 μm at a temperature of 77 K. The results reveal new opportunities for bandgap engineering of semiconductor structures based on InAs/GaSb, which are designed for optoelectronic devices operating in the infrared range, provided by MOVPE.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structure property relationships in gallium oxide thin films grown by pulsed laser deposition [Structure property relationships in Ga 2 O 3 thin films grown by pulsed laser deposition]

Beta-gallium oxide (β-Ga 2 O 3 ) is of increasing interest to the optoelectronic community for transparent conductor and power electronic applications. Considerable variability exists in the literature on the growth and doping of Ga 2 O 3 films, especially as a function of growth approach, temperature, and oxygen partial pressure. Here pulsed laser deposition (PLD) was used to grow high-quality β-Ga 2 O 3 films on (0001) sapphire and (–201) Ga 2 O 3 single crystals and to explore the growth, stability, and dopability of these films as function of temperature and oxygen partial pressure. As a result, there is a strong temperature dependence to the phase formation, morphology, and electronic properties of β-Ga 2 O 3 from 350 to 550 °C.

14 SOLAR ENERGY↗
DOE OSTI2022

Switching the conductance of a single molecule: Lessons from molecular junctions

The concept of using single molecules as functional building blocks in electronic circuitry represents the ultimate device miniaturization and has garnered tremendous attention from physics, chemistry, and engineering. Recent advances in single-molecule junction techniques have enabled direct investigation of charge transport in a quasi-one-dimensional conduction channel composed of an individual molecule. Furthermore, one of the main research focuses over the past decade has been to understand the conductance switching effect of single molecules as it is essential for developing molecular-scale optoelectronics, computing, and sensing applications. In this perspective, we highlight the established physical and chemical mechanisms for single-molecule conductance switching behavior and examine the associated stimuli in single-molecule junction systems.

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

Materials and Device Architectures for Organic Solar Cell Applications: Cooperative Research and Development Final Report, CRADA Number CRD-09-355

The Centre for Organic Photonics & Electronics (COPE) at UQ has been successful in acquiring funding from the Australian Center for Advanced Photovoltaics (ACAP), which is the Australian partner of the Australia-US Institute for Advanced Photovoltaics (AUSIAPV). NREL is a key partner in AUSIAPV (along with other US research institutions (ASU, Sandia NL, LBNL, Stanford, Georgia Tech and UCSB). NREL will collaborate with COPE to advance the science and technology of organic materials for solar cell applications. COPE has significant programs in the development and understanding of new materials for organic optoelectronic applications and, in particular, for thin film bulk heterojunction (BHJ) solar cells and Organic Photodiodes (OPDs). NREL has significant established research programs in all aspects of organic photovoltaic technology and has well-developed expertise in the area of materials characterization, photocarrier transport measurements as well as device fabrication, scale-up and stability. This collaboration will combine the expertise of the two institutions to work towards demonstrating the scalability of organic materials for BHJ and OPD applications by measuring the fundamental properties of the materials as a function of processing and evaluating their performance and stability in photovoltaic devices under simulated illumination conditions. Currently, both NREL and UQ have individual organic material development and processing efforts and have independently demonstrated several prototype materials and device architectures as promising candidates for organic solar cells and OPDs. This CRADA will align these efforts building upon strengths of the two institutions to further design and demonstrate materials and device architectures to advance organic BHJ solar cells and OPDs. It should also be clearly noted that we foreshadow possible expansion of collaborative research activities between COPE and NREL, which currently lie outside the scope of the current statement of work, which will be amended as required by mutually executed written modifications to this CRADA.

14 SOLAR ENERGY↗
DOE OSTI2019

Many-body effects in transport and energy transfer

Many-body physics is common in defining responses of nanoscale to external perturbations such as bias, optical driving, temperature gradient. When applied to open systems these perturbations lead to matter and energy transfer between the system and its surroundings (baths) and/or cause intra-system dynamics. While many different theoretical techniques have been developed to describe system responses, not all of them are convenient (or even appropriate) when applied at nanoscale. Traditional theoretical techniques are either based on kinetic schemes (e.g., Redfield-Lindblad quantum master equation) or utilize quasiparticle description (e.g., single-particle scattering theory, input-output formalism, standard nonequilibrium Green’s functions technique). The former fails to account for quantum mechanics of the system-bath interface and may fail qualitatively when used in open interacting systems. The latter is inconvenient when many-body states description of the system is preferable, which is usual, e.g., in molecular optical spectroscopy. This project was devoted to development of new nonequilibrium Green’s function (NEGF) techniques and application of standard and many-body flavors of the NEGF to description of charge and energy transport, optical response, nonadiabatic molecular dynamics, and thermodynamics of nanoscale devices in general, and, in particular, of single-molecule junctions. In particular, Hubbard NEGF (new many-body flavor of the NEGF) was introduced as a new technique especially convenient in treatment of optoelectronic experiments in single-molecule junctions and useful in discussion of bias induced nuclear dynamics in junctions. The research also led to further technique developments and applications beyond the timing of this Award.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Synthetic Control of the Photoluminescence Stability of Organolead Halide Perovskites

An optimized synthetic procedure for preparing photostable nanocrystalline methylammonium lead halide materials is reported. The procedure was developed by adjusting the lead halide to methylammonium/octylammonium halide precursor ratio. At a high precursor ratio (1:3), a blue-shifted photoinduced luminescence peak is measured at 642 nm for CH 3 NH 3 PbI 3 with 0.01 to 12 mJ pulsed-laser irradiation. The appearance of this peak is reversible over 300 min upon blocking the irradiation. In order to determine if the peak is the result of a phase change, in situ x-ray diffraction measurements were performed. No phase change was measured with an irradiance that causes the appearance of the photoinduced luminescence peak. Luminescence microscpectroscopy measurements showed that the use of a lower precursor ratio (1:1.5) produces CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 perovskites that are stable over 4 min of illumination. Given the lack of a measured phase change, and the dependence on the precursor ratio, the photoinduced luminesce peak may derive from surface trap states. Finally, the enhanced photostability of the resulting perovskite nanocrystals produced with the optimized synthetic procedure supports their use in stable optoelectronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Recent Progress in Transparent Conductive Materials for Photovoltaics

Transparent conducting materials (TCMs) are essential components for a variety of optoelectronic devices, such as photovoltaics, displays and touch screens. In recent years, extensive efforts have been made to develop TCMs with both high electrical conductivity and optical transmittance. Based on material types, they can be mainly categorized into the following classes: metal oxides, metal nanowire networks, carbon-material-based TCMs (graphene and carbon nanotube networks) and conjugated conductive polymers (PEDOT:PSS). This review will discuss the fundamental electrical and optical properties, typical fabrication methods and the applications in solar cells for each class of TCMs and highlight the current challenges and potential future research directions.

14 SOLAR ENERGY↗
DOE OSTI2022

Light-Driven Charge Transport and Optical Sensing in Molecular Junctions

Probing charge and energy transport in molecular junctions (MJs) has not only enabled a fundamental understanding of quantum transport at the atomic and molecular scale, but it also holds significant promise for the development of molecular-scale electronic devices. Recent years have witnessed a rapidly growing interest in understanding light-matter interactions in illuminated MJs. These studies have profoundly deepened our knowledge of the structure–property relations of various molecular materials and paved critical pathways towards utilizing single molecules in future optoelectronics applications. In this article, we survey recent progress in investigating light-driven charge transport in MJs, including junctions composed of a single molecule and self-assembled monolayers (SAMs) of molecules, and new opportunities in optical sensing at the single-molecule level. We focus our attention on describing the experimental design, key phenomena, and the underlying mechanisms. Specifically, topics presented include light-assisted charge transport, photoswitch, and photoemission in MJs. Emerging Raman sensing in MJs is also discussed. Finally, outstanding challenges are explored, and future perspectives in the field are provided.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Unveiling interfaces between In-rich and Ga-rich GaInP vertical slabs of laterally composition modulated structures

Here, we report changes at the interface between Ga-rich/In-rich GaInP vertical slabs in laterally composition modulated (LCM) GaInP as a function of the V/III ratio. The photoluminescence exhibits satellite peaks, indicating that the parasitic potential between the GaInP vertical slabs disappears as the V/III ratio decreases. However, a high V/III ratio leads to an abrupt interface, increasing the parasitic potential because of the phosphorus-amount-dependent diffusion of group-III atoms during growth. These results suggest that the V/III ratio is an important parameter that must be wisely chosen in designing optoelectronic devices incorporating LCM structure.

36 MATERIALS SCIENCE↗
NASA NTRS1997

A Chemical and Structural Study of the AlN-Si Interface

The growth of low defect density heteroepitaxial AlN has great implications for optoelectronic and high power devices since the AlN can be used either as device material or as a buffer layer for the overgrowth of other group-III nitrides. In this work, the results of transmission electron microscopy (TEM) involving both high resolution imaging and electron energy loss spectroscopy (EELS) of AlN/Si layers is reported and the relationship between Si-Al-N interactions and the misorientation of AlN nuclei is elucidated.

epitaxial optoelectronic silicon gallium nitride↗
NASA NTRSDate not supplied

Photonics for Space Flight Instruments

For the past 25 years, the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center’s Photonics Group in the Engineering Directorate has been substantially contributing to the flight design, development, production, testing and integration of many science and navigational instruments. The group has an extensive background in screening, qualifying, development and integration of commercial components for spaceflight applications. They have been willing to communicate lessons learned in packaging, part construction, materials selection, testing, and other facets of the design and production process critical to implementation for high-reliability systems. Summarized here is the last ten years of instrumentation development lessons learned and data collected from the subsystems down to the optoelectronic component level.

Spaceflight↗
NASA NTRSDate not supplied

Photonics for Space Flight Instruments

The Photonics group top level processes regarding development and qualification of space flight hardware for optoelectronic components and optical systems along with our contributions and successes with LIDAR systems, space flight reliability heritage, and our testing capabilities are conveyed with this power point presentation.

Optoelectronics components↗
DOE OSTI2012

Doping and Alloying in the Solution-Phase Synthesis of Germanium Nanocrystals

Group IV nanocrystals (NCs) are receiving increased attention as a potentially non-toxic nanomaterial for use in a number of important optoelectronic applications (e.g., solar photoconversion, photodetectors, LEDs, biological imaging). With these goals in mind, doping and alloying with Group III, IV, and V elements may play a major role in tailoring the NC properties, such as developing n-type and p-type conductivity through substitutional doping, as well as affecting the optical absorption, emission, and overall charge transport in a NC film. Here we present an extension of the mixed-valence iodide precursor methodology to incorporate Group III, IV, and V elements to produce E-GeNC materials. All main-group elements (E) that surround Ge on the periodic table (i.e., E = Al, Si, P, Ga, As, In, Sn, and Sb) can be incorporated via this methodology. The extent to which the dopant elements are included will be discussed, along with the optical absorbance, emission, and related properties of the NCs. In addition, the effect of the dopant elements on the NC growth kinetics will be discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

The effects of electronic impurities and electron-hole recombination dynamics on large-grain organic-inorganic perovskite photovoltaic efficiencies

Hybrid organic-inorganic perovskites have attracted considerable attention after promising developments in energy harvesting and other optoelectronic applications. However, further optimization will require a deeper understanding of the intrinsic photophysics of materials with relevant structural characteristics. Here, the dynamics of photoexcited charge carriers in large-area grain organic-inorganic perovskite thin films is investigated via confocal time-resolved photoluminescence spectroscopy. It is found that the bimolecular recombination of free charges is the dominant decay mechanism at excitation densities relevant for photovoltaic applications. Bimolecular coefficients are found to be on the order of 10 –9 cm 3 s –1 , comparable to typical direct-gap semiconductors, yet significantly smaller than theoretically expected. It is also demonstrated that there is no degradation in carrier transport in these thin films due to electronic impurities. Here, suppressed electron–hole recombination and transport that is not limited by deep level defects provide a microscopic model for the superior performance of large-area grain hybrid perovskites for photovoltaic applications.

14 SOLAR ENERGY↗