Search NASA⌕ Search

SEARCH · Search NASA

Results for “LIGHT 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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Source apportionment of soot particles and aqueous-phase processing of black carbon coatings in an urban environment

Abstract. The impacts of soot particles on climate and human health depend on the concentration of black carbon (BC) as well as the thickness and composition of the coating material, i.e., organic and inorganic compounds internally mixed with BC. In this study, the size-resolved chemical composition of BC-containing aerosol was measured using a high-resolution soot particle aerosol mass spectrometer (SP-AMS) during wintertime in Fresno, California, a location influenced by abundant combustion emissions and frequent fog events. Concurrently, particle optical properties were measured to investigate the BC absorption enhancement. Positive matrix factorization (PMF) analysis was performed on the SP-AMS mass spectral measurements to explore the sources of soot particles and the atmospheric processes affecting the properties of BC coatings. The analysis revealed that residential woodburning and traffic are the dominant sources of soot particles. Alongside primary soot particles originating from biomass burning (BBOABC) and vehicles (HOABC) two distinct types of processed BC-containing aerosol were identified: fog-related oxidized organic aerosol (FOOABC) and winter-background OOABC (WOOABC). Both types of OOABC showed evidence of having undergone aqueous processing, albeit with differences. The concentration of FOOABC was substantially elevated during fog events, indicating the formation of aqueous secondary organic aerosol (aqSOA) within fog droplets. On the other hand, WOOABC was present at a relatively consistent concentration throughout the winter and was likely related to the formation of secondary organic aerosol (SOA) in both the gas phase and aerosol liquid water. By comparing the chemical properties and temporal variations in FOOABC and WOOABC, we gain insights into the key aging processes of BC aerosol. It was found that aqueous-phase reactions facilitated by fog droplets had a significant impact on the thickness and chemical composition of BC coatings, thereby affecting the light absorption and hygroscopic properties of soot particles. These findings underscore the important role of chemical reactions occurring within clouds and fogs and influencing the climate forcing of BC aerosol in the atmosphere.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Imaging Nanoscale Energy Transport and Conversion with Ultrafast Electron Microscopy (Final Technical Report)

Light-matter interactions are ubiquitous in nature and reside at the heart of innumerable technologies. The cascade of processes that occur when a material absorbs a photon of light are exceedingly complex and are interwoven in both space and time, rendering precise determination of the atomic-scale and ultrafast mechanisms immensely challenging. The advent of methods for generating short pulses of light several decades ago led to major advances in understanding the initial moments of light absorption and the resultant effects, though directly interrogating the response of the atoms within the material continued to prove challenging. More recently, methods for generating ultrashort pulses of X-rays and fast electrons have opened the way to probing photoinduced structural dynamics of a wide range of matter in multiple phases. An especially promising laboratory-scale method is ultrafast electron microscopy (UEM), wherein the modalities of conventional transmission electron microscopes (imaging, diffraction, spectroscopy) are extended into the femtosecond temporal regime. Here, the ultrafast imaging and diffraction modalities of UEM were used to study the transient structural aspects of photoexcitation of semiconducting materials (e.g., spatially-resolved electron-phonon coupling, excitation and emission of acoustic phonons, and discrete nanoscale scattering processes). The project had three main objectives: (1) determination of the excitation mechanisms of dense, hypersonic charge-carrier waves and the spatially mediated means by which they couple to the lattice via coherent phonon emission, especially with UEM imaging, wherein effects of nanoscale structural and morphological features on the coupling and relaxation dynamics are expected to dictate nucleation sites and preferred wave vectors, (2) elucidation of photoinduced acoustic-phonon seeding, emergence, propagation, and decay over nanoscale crystal regions and especially with respect to local strain fields and atomic-scale disruptions in lattice order, and (3) interwoven with the first two were efforts aimed at realizing combined angstrom-femtosecond spatiotemporal imaging with UEM. The outcomes and impacts of this project were the generation of new knowledge with respect to fundamental light-matter interactions and, especially, the spatially-mediated excitation and evolution of the structural response of materials following coherent photoexcitation. Importantly, the spatial and temporal resolutions of the UEM imaging modalities used are well-suited for such studies and enable spatially-resolved mechanisms to be determined as a function of atomic order, structural features, and morphology. In addition, ultrafast crystallographic measurements were used to correlate real- and reciprocal-space dynamics in order to determine atomic-scale preferential wave vectors and ultrafast scattering mechanisms, especially as dictated by specimen boundary conditions. The obtained results, as detailed in peer-reviewed publications and presentations, illustrate the importance of ultrafast, angstrom-scale real-space imaging for developing a comprehensive understanding of energy transport and conversion in materials.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Twisted Crystalline Organic Semiconductor Photodetectors

Optoelectronic properties of anisotropic crystals vary with direction requiring that the orientation of molecular organic semiconductor crystals is controlled in optoelectronic device active layers to achieve optimal performance. Here, in this work, a generalizable strategy to introduce periodic variations in the out-of-plane orientations of 5,11-bis(triisopropylsilylethynyl)anthradithiophene (TIPS ADT) crystals is presented. TIPS ADT crystallized from the melt in the presence of 16 wt.% polyethylene (PE) forms banded spherulites of crystalline fibrils that twist in concert about the radial growth direction. These spherulites exhibit band-dependent light absorption, photoluminescence, and Raman scattering depending on the local orientation of crystals. Mueller matrix imaging reveals strong circular extinction (CE), with TIPS ADT banded spherulites exhibiting domains of positive or negative CE signal depending on the crystal twisting sense. Furthermore, orientation-dependent enhancement in charge injection and extraction in films of twisted TIPS ADT crystals compared to films of straight crystals is visualized in local conductive atomic force microscopy maps. This enhancement leads to 3.3- and 6.2-times larger photocurrents and external quantum efficiencies, respectively, in photodetectors comprising twisted crystals than those comprising straight crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Quasi‐Homojunction Organic Nonfullerene Photovoltaics Featuring Fundamentals Distinct from Bulk Heterojunctions

Abstract In contrast to classical bulk heterojunction (BHJ) in organic solar cells (OSCs), the quasi‐homojunction (QHJ) with extremely low donor content (≤10 wt.%) is unusual and generally yields much lower device efficiency. Here, representative polymer donors and nonfullerene acceptors are selected to fabricate QHJ OSCs, and a complete picture for the operation mechanisms of high‐efficiency QHJ devices is illustrated. PTB7‐Th:Y6 QHJ devices at donor:acceptor (D:A) ratios of 1:8 or 1:20 can achieve 95% or 64% of the efficiency obtained from its BHJ counterpart at the optimal D:A ratio of 1:1.2, respectively, whereas QHJ devices with other donors or acceptors suffer from rapid roll‐off of efficiency when the donors are diluted. Through device physics and photophysics analyses, it is observed that a large portion of free charges can be intrinsically generated in the neat Y6 domains rather than at the D/A interface. Y6 also serves as an ambipolar transport channel, so that hole transport as also mainly through Y6 phase. The key role of PTB7‐Th is primarily to reduce charge recombination, likely assisted by enhancing quadrupolar fields within Y6 itself, rather than the previously thought principal roles of light absorption, exciton splitting, and hole transport.

Chemistry↗
DOE OSTI2024

Engineering Ultrathin Alloy Shell in Au@AuPd Core-Shell Nanoparticles for Efficient Plasmon-Driven Photocatalysis

Bimetallic core-shell nanoparticles (NPs) possessing a synergetic coupling of plasmonic and catalytic metals have emerged as promising prototypes for efficient plasmon-driven photocatalysis. Here, Au@AuPd core-shell NPs composed of Au core NP and ultrathin AuPd shell are introduced to acquire improved light utilization efficiency in photocatalytic selective oxidation. With systematical control of the composition of the ultrathin alloy shell, it reveals that the Au@AuPd core-shell NPs with 10 at% Pd (in the single-atom alloy regime) is an effective nanostructure capable of maximizing the quantum yield of plasmon-induced light absorption and optimizing the surface electronic structure for catalytic reactions. This controlled system provides new insights into shell engineering for enhancing photocatalytic performance via the regulation of energy funneling processes in core-shell nanocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multilayer Lateral Heterostructures of Van Der Waals Crystals with Sharp, Carrier–Transparent Interfaces

Abstract Research on engineered materials that integrate different 2D crystals has largely focused on two prototypical heterostructures: Vertical van der Waals stacks and lateral heterostructures of covalently stitched monolayers. Extending lateral integration to few layer or even multilayer van der Waals crystals could enable architectures that combine the superior light absorption and photonic properties of thicker crystals with close proximity to interfaces and efficient carrier separation within the layers, potentially benefiting applications such as photovoltaics. Here, the realization of multilayer heterstructures of the van der Waals semiconductors SnS and GeS with lateral interfaces spanning up to several hundred individual layers is demonstrated. Structural and chemical imaging identifies {110} interfaces that are perpendicular to the (001) layer plane and are laterally localized and sharp on a 10 nm scale across the entire thickness. Cathodoluminescence spectroscopy provides evidence for a facile transfer of electron‐hole pairs across the lateral interfaces, indicating covalent stitching with high electronic quality and a low density of recombination centers.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Development and Prospects of Halide Perovskite Single Crystal Films

Halide perovskite single crystal (HPSC) films have demonstrated extraordinary performance in solar cells, photodetectors, and lighting applications, owing to the high carrier mobility, long carrier diffusion length, tunable bandgap, and large light absorption coefficients of these materials. Here, the recent development of the major HPSC thin films is reviewed systematically, including MAPbI 3 , α-FAPbI 3 , MAPbBr 3 , CsPbBr 3 , with special emphasis on different classes of fabrication methods and thin-film characteristics. So finally, the conclusion and prospects in this field are discussed in detail. It is anticipated that the HPSC thin films will lead to a compelling future for the rising electronic applications.

MAPbI3↗
DOE OSTI2020

Efficient, Thermally Stable, and Mechanically Robust All-Polymer Solar Cells Consisting of the Same Benzodithiophene Unit-Based Polymer Acceptor and Donor with High Molecular Compatibility

All-polymer solar cells (all-PSCs) are a highly attractive class of photovoltaics for wearable and portable electronics due to their excellent morphological and mechanical stabilities. Recently, new types of polymer acceptors (P A s) consisting of non-fullerene small molecule acceptors (NFSMAs) with strong light absorption have been proposed to enhance the power conversion efficiency (PCE) of all-PSCs. However, polymerization of NFSMAs often reduces entropy of mixing in PSC blends and prevents the formation of intermixed blend domains required for efficient charge generation and morphological stability. One approach to increase compatibility in these systems is to design P A s that contain the same building blocks as their polymer donor (P D ) counterparts. Here, a series of NFSMA-based P A s [P(BDT2BOY5-X), (X = H, F, Cl)] are reported, by copolymerizing NFSMA (Y5-2BO) with benzodithiophene (BDT), a common donating unit in high-performance P D s such as PBDB-T. All-PSC blends composed of PBDB-T PD and P(BDT2BOY5-X) P A show enhanced molecular compatibility, resulting in excellent morphological and electronic properties. Specifically, PBDB-T:P(BDT2BOY5-Cl) all-PSC has a PCE of 11.12%, which is significantly higher than previous PBDB-T:Y5-2BO (7.02%) and PBDB-T:P(NDI2OD-T2) (6.00%) PSCs. Additionally, the increased compatibility of these all-PSCs greatly improves their thermal stability and mechanical robustness. For example, the crack onset strain (COS) and toughness of the PBDB-T:P(BDT2BOY5-Cl) blend are 15.9% and 3.24 MJ m -3 , respectively, in comparison to the PBDB-T:Y5-2BO blends at 2.21% and 0.32 MJ m -3 .

14 SOLAR ENERGY↗
DOE OSTI2026

Achieving 20.1% Efficiency in Organic Solar Cells Through Interconnected Fibrillar Networks via Local Molecular Stacking

ABSTRACT The performance of organic solar cells (OSCs) is governed by how molecular packing evolves into interconnected networks that facilitate exciton dissociation and charge transport. Using an all‐small‐molecule blend DR3TSBDT:Y6 as a model system, we study how local molecular stacking evolves into performance‐relevant morphology during solvent vapor annealing (SVA) and subsequent thermal annealing (TA). SVA promotes end‐to‐end stacking of amorphous acceptors to form interconnected fibrils, while TA compacts inter‐fibril spacing without disrupting favorable local order. Such molecular‐to‐morphological refinements broaden light absorption, enhance charge transport, and markedly improve device efficiency. Extending this approach to additional blend systems (D18:Y6, D18:L8‐BO, and DR3TSBDT:L8‐BO) yields similar structural evolution and performance gains, with the D18:L8‐BO system achieving up to 20.10% PCE. Our study establishes control over local stacking in amorphous acceptors into fibrillar networks as a general and effective route to realize high‐performance OSCs.

Wu, Junying↗
DOE OSTI2025

Fe‐Triazolate Metal–Organic Frameworks as Water Oxidation Catalysts with Dual Photoanode Functionality

Artificial photosynthesis is an emerging technology that achieves renewable fuels, such as hydrogen, from sunlight. Its realization depends on finding highly active and stable catalysts of water splitting and photoactive materials for light absorption. To be scalable, these should contain only abundant elements. Here, for the first time, Fe-triazolate (Fe(ta) 2 ) and its metal substituted derivatives (Fe-Metal(ta) 2 ) Metal-organic frameworks (MOFs) are characterized as new dual-function materials for photo-absorption and water oxidation catalysis in acidic media. The materials were studied by a range of structural, spectroscopic, and computational density functional theory (DFT) techniques. Fe(ta) 2 and Fe-Mn(ta) 2 were found to be highly active and stable in chemical and photochemical water oxidation, and in addition function as photoanodes, with photo-electrocatalytic currents (∼2.00 x 10 −3 Acm −2 at + 1.4 V vs. Ag/AgCl) at pH = 1. The possibility of a unique catalytic mechanism where O─O bond formation is possible from the coupling of two adjacent Fe IV = O fragments was demonstrated by DFT analysis. Thus, Fe-triazolate MOF has been established as a new, stable, scalable, versatile, and efficient platform for sustainable energy conversion in the realm of artificial photosynthesis.

Artificial photosynthesis↗
DOE OSTI2025

Homologous Ladder Cyclohexasilanes

Here, we report the synthesis of five new examples of ladder cyclohexasilanes, possessing up to three consecutive fused rings and differing in relative ring fusion configuration and side chain structure. By coupling a 1,4-dipotassiooligosilyl dianion to a cyclohexasilane, we obtained bi- and tricyclic ladder cyclohexasilanes. Combined experimental and theoretical studies suggested that annulation could favor the cis configuration under kinetic control, while the trans configuration predominates under thermodynamic control. Computational studies show that with each additional ring in the trans-diastereomeric series, the predicted onset of light absorption shifts to longer wavelengths.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Surface‐modified Ag@Ru‐P25 for photocatalytic CO 2 conversion with high selectivity over CH 4 formation at the solid–gas interface

Systematic optimization of the photocatalyst and investigation of the role of each component is important to maximizing catalytic activity and comprehending the photocatalytic conversion of CO 2 reduction to solar fuels. A surface-modified Ag@Ru-P25 photocatalyst with H 2 O 2 treatment was designed in this study to convert CO 2 and H 2 O vapor into highly selective CH 4 . Ru doping followed by Ag nanoparticles (NPs) cocatalyst deposition on P25 (TiO 2 ) enhances visible light absorption and charge separation, whereas H 2 O 2 treatment modifies the surface of the photocatalyst with hydroxyl (–OH) groups and promotes CO 2 adsorption. High-resonance transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure techniques were used to analyze the surface and chemical composition of the photocatalyst, while thermogravimetric analysis, CO 2 adsorption isotherm, and temperature programmed desorption study were performed to examine the significance of H 2 O 2 treatment in increasing CO 2 reduction activity. The optimized Ag 1.0 @Ru 1.0 -P25 photocatalyst performed excellent CO 2 reduction activity into CO, CH 4 , and C 2 H 6 with a ~95% selectivity of CH 4 , where the activity was ~135 times higher than that of pristine TiO 2 (P25). For the first time, this work explored the effect of H 2 O 2 treatment on the photocatalyst that dramatically increases CO 2 reduction activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Photoredox Organic Synthesis Employing Heterogeneous Photocatalysts with Emphasis on Halide Perovskite

Abstract Lately, heterogeneous semiconductor materials have been explored as an emerging type of efficient photocatalyst for photoredox organic synthesis. Among these semiconductors, lead halide perovskite materials demonstrate unique properties towards excellent charge separation and charge transfer, extremely long charge carrier migration, high efficiency in visible light absorption, and long excited states lifetimes, etc., as proved in ground‐breaking solar cell applications, garnering necessary merits for an efficient catalytic system for photoredox organic reactions. Here, the latest progress in heterogeneous semiconductor materials towards this endeavor is examined, with particular emphasis on lead halide perovskite nanocrystals (NCs) in photocatalytic organic synthesis.

Lin, Yixiong↗
DOE OSTI2022

Monolayer Plasmonic Nanoframes as Large‐Area, Broadband Metasurface Absorbers

Abstract Broadband absorbers are useful ultraviolet protection, energy harvesting, sensing, and thermal imaging. The thinner these structures are, the more device‐relevant they become. However, it is difficult to synthesize ultrathin absorbers in a scalable and straightforward manner. A general and straightforward synthetic strategy for preparing ultrathin, broadband metasurface absorbers that do not rely on cumbersome lithographic steps is reported. These materials are prepared through the surface‐assembly of plasmonic octahedral nanoframes (NFs) into large‐area ordered monolayers via drop‐casting with subsequent air‐drying at room temperature. This strategy is used to produce three types of ultrathin broadband absorbers with thicknesses of ≈200 nm and different lattice symmetries (loose hexagonal, twisted hexagonal, dense hexagonal), all of which exhibit efficient light absorption (≈90%) across wavelengths ranging from 400–800 nm. Their broadband absorption is attributed to the hollow morphologies of the NFs, the incorporation of a high‐loss material (i.e., Pt), and the strong field enhancement resulting from surface assembly. The broadband absorption is found to be polarization‐independent and maintained for a wide range of incidence angles (±45°). The ability to design and fabricate broadband metasurface absorbers using this high‐throughput surface‐based assembly strategy is a significant step toward the large‐scale, rapid manufacturing of nanophotonic structures and devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Photocatalytic Hydrogen Evolution Using Mesoporous Honeycomb Iron Titanate

Mesoporous honeycomb iron titanate using a sol-gel, evaporation-induced self-assembly method is synthesized. A triblock copolymer, F127, serves as a structure-directing agents, with iron chloride and titanium (IV) isopropoxide as inorganic precursors. The strong intermolecular force of attraction among urea, metal precursors, and polymer led to the formation of the mesoporous honeycomb structure. The study of physicochemical properties using different techniques reveals the formation of microstructures with a remarkable degree of porosity. The amorphous iron titanate outperforms the photochemical generation of H 2 due to its disorderly structural arrangement and incomplete crystal formation. The randomness on the structure provides more area for catalytic reaction by providing more contact with the reactant and superior light absorption capability. The high amount of hydrogen gas, 40.66 mmolg -1 h -1 , is observed in the investigation over 3 h of activity for the iron titanate honeycomb sample. This yield is a more significant amount compared to the obtained for the commercially available TiO 2 (23.78 mmolg -1 h -1 ). The iron titanate materials synthesized with low-cost materials and methods are very effective and have the potential for hydrogen generation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Regulation of Electron Cloud Density by Electronic Effects of Substituents to Optimize Photocatalytic H 2 Evolution of Carbon Dots

Carbon dots (CDs) have a wide light absorption range, which are promising candidates for photocatalytic water splitting H 2 evolution, but they show low activity for hydrogen evolution reaction (HER) due to the slow transfer efficiencies of photogenerated carriers. The electron cloud density of photocatalyst is essential for the separation and migration of photogenerated carriers. In this study, the effect mechanism of electron cloud density regulated by the substituents with different electronic effects on the photocatalytic HER of glucose-based CDs is clarified. CDs-SO 3 H and CDs-OH are first obtained by introducing electron-drawing group (–SO 3 H) and electron-donating group (–OH) using a tailoring post-processing strategy. Experimental results show that the H 2 yield catalyzed by CDs-SO 3 H is 89.95 µmol•g –1 in 4 h, which is about four times that of CDs, and 7.4 times that of CDs-OH. The –SO 3 H induces a much negative energy band and high electron cloud density on CDs edges, promoting the separation and transfer of photogenerated carriers; while the CDs-OH exhibits a high positive charge density and an upward energy band, hindering the surface complexation of electron-hole pairs and HER. Furthermore, this study will provide an insight into the design of CDs catalysts with efficient photocatalytic HER at a molecular level.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Efficient Perovskite Solar Cells Achieved via Rapid Photonic Annealing of all Stacking Layers: Unveiling the Crystallization Energy Window

In this study, we report high-performance perovksite solar cells (PSCs) with rapid photonic annealing (RPA) of all stacking layers, enabled by ultraviolet (UV) light-emitting diode (LED) sources, to replace lengthy and energy-intensive thermal annealing (TA). The UV-LED annealing technique allows for layer-specific annealing, where the selected light source provides a precise UV wavelength for maximizing the amount of light absorption by the target layer. The disparity in optical absorption between the target layer and the underlying films allows the stack of the underlying films to remain relatively unaffected, making this process ideal for heating sensitive substrates. Along with a systematic investigation into the layer-specific annealing mechanism of RPA, the results demonstrated that this UV-LED-based photonic annealing of all stacking layers (7 s for perovskite absorber) can produce PSCs with the power conversion efficiency (PCE) of over 23%, the highest reported among optically annealed PSCs. Moreover, the RPA device retains over 80% of the initial PCE over 1000 h under continuous 1 sun illumination at 55 °C and 30%–60% relative humidity (RH), while TA control device drops to 50% of its initial efficiency. Furthermore, these findings represent significant strides toward achieving rapid, cost-effective, and scalable manufacturing of commercial perovskite photovoltaics (PV).

14 SOLAR ENERGY↗
DOE OSTI2024

An Emerging Trend in the Synthesis of Iron Titanate Photocatalyst Toward Water Splitting

Hydrogen gas is a prominent focus in pursuing renewable and clean alternative energy sources. The quest for maximizing hydrogen production yield involves the exploration of an ideal photocatalyst and the development of a simple, cost-effective technique for its generation. Iron titanate has garnered attention in this context due to its photocatalytic properties, affordability, and non-toxic nature. Over the years, different synthesis routes, different morphologies, and some modifications of iron titanate have been carried out to improve its photocatalytic performance by enhancing light absorption in the visible region, boosting charge carrier transfer, and decreasing recombination of electrons and holes. The use of iron titanate photocatalyst for hydrogen evolution reaction has seen an upward trend in recent times, and based on available findings, more can be done to improve the performance. This review paper provides a comprehensive overview of the fundamental principles of photocatalysis for hydrogen generation, encompassing the synthesis, morphology, and application of iron titanate-based photocatalysts. The discussion delves into the limitations of current methodologies and present and future perspectives for advancing iron titanate photocatalysts. By addressing these limitations and contemplating future directions, the aim is to enhance the properties of materials fabricated for photocatalytic water splitting.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗