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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 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Evolution of Surface Copper(II) Environments in Cu 2–x Se Nanoparticles

Cu 2–x Se nanoparticles are part of a promising class of alternative plasmonic materials where the location, stability, and structural impact of charge carrier generation are crucial to their optoelectronic performance. Electron paramagnetic resonance spectroscopy is used to identify the location and dynamics of Cu 2+ environments that form upon air-induced oxidation of Cu 2–x Se nanoparticles. The results indicate the formation of two distinct Cu 2+ environments at or near the surface of the nanoparticle. The first environment can be assigned to Cu 2+ bound to oleylamine capping ligands, and the second can be assigned to Cu 2+ located in CuO domains. In addition, these experiments indicate that the observed Cu 2+ environments are consistent with vacancy formation on the Cu sublattice, which are mobile (i.e., vacancy hopping) at temperatures down to 180 K. Taken together, our results elucidate time scales of air-mediated Cu oxidation in Cu 2–x Se nanoparticles, the chemical environments of the resulting Cu 2+ species, and the impact of this oxidation on the overall particle crystallographic structure and optoelectronic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Synthesis of Polycrystalline Ruddlesden–Popper Organic Lead Halides and Their Growth Dynamics

Ruddlesden–Popper organic lead halides (RPOLHs) are in the material science spotlight because of their remarkable optoelectronic properties, tailorable compositions, and improved ambient stability over their three-dimensional perovskite analogues. In this report, we introduce a new synthesis method for RPOLHs with general composition L 2 [FAPbI 3 ] n–1 PbI 4 [L = butylammonium (BA) or benzylammonium (BZA), FA = formamidinium, and n = 1 and 2]. Here, our method yields polycrystalline materials useful for thin-film fabrication for optoelectronic applications. Furthermore, we report the growth dynamics of BA 2 [FAPbI 3 ]PbI 4 using in situ small-angle X-ray scattering, revealing that the slabs grow within the first seconds of the reaction and then self-assemble into bulk crystallites.

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

Structural Tolerance Factor Approach to Defect-Resistant I 2 -II-IV-X 4 Semiconductor Design

Recent work on quaternary semiconductors Cu 2 BaSn(S,Se) 4 and Ag 2 BaSnSe 4 for photovoltaic and thermoelectric applications, respectively, has shown the promise of exploring the broader family of defect-resistant I 2 -II-IV-X 4 materials (where I, II, and IV refer to the formal oxidation state of the metal cations and X is a chalcogen anion) with tetrahedrally coordinated I/IV cations and larger II cations (i.e., Sr, Ba, Pb, and Eu) for optoelectronic and energy-related applications. Chemical dissimilarity among the II and I/IV atoms represents an important design motivation because it presents a barrier to antisite formation, which otherwise may act as electronically harmful defects. We herein show how all 31 experimentally reported I 2 -II-IV-X 4 examples (with large II cations and tetrahedrally coordinated smaller I/IV cations), which form within five crystal structure types, are structurally linked. Based on these structural similarities, we derive a set of tolerance factors that serve as descriptors for phase stability within this family. Despite common usage in the well-studied perovskite system, Shannon ionic radii are found to be insufficient for predicting metal–chalcogen bond lengths, pointing to the need for experimentally derived correction factors as part of an empirically driven learning approach to structure prediction. Here, we use the tolerance factors as a predictive tool and demonstrate that four new I 2 -II-IV-X 4 compounds, Ag 2 BaSiS 4 , Ag 2 PbSiS 4 , Cu 2 PbGeS 4 , and Cu 2 SrSiS 4 , can be synthesized in correctly predicted phases. One of these compounds, Ag 2 PbSiS 4 , shows potentially promising optoelectronic properties for photovoltaic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Wide Band Gap Chalcogenide Semiconductors

Wide band gap semiconductors are essential for today’s electronic devices and energy applications because of their high optical transparency, controllable carrier concentration, and tunable electrical conductivity. The most intensively investigated wide band gap semiconductors are transparent conductive oxides (TCOs), such as tin-doped indium oxide (ITO) and amorphous In–Ga–Zn–O (IGZO), used in displays and solar cells, carbides (e.g., SiC) and nitrides (e.g., GaN) used in power electronics, and emerging halides (e.g., γ-CuI) and 2D electronic materials (e.g., graphene) used in various optoelectronic devices. Compared to these prominent materials families, chalcogen-based (Ch = S, Se, Te) wide band gap semiconductors are less heavily investigated but stand out because of their propensity for p-type doping, high mobilities, high valence band positions (i.e., low ionization potentials), and broad applications in electronic devices such as CdTe solar cells. This manuscript provides a review of wide band gap chalcogenide semiconductors. First, we outline general materials design parameters of high performing transparent semiconductors, as well as the theoretical and experimental underpinnings of the corresponding research methods. We proceed to summarize progress in wide band gap (EG > 2 eV) chalcogenide materials—namely, II–VI MCh binaries, CuMCh 2 chalcopyrites, Cu 3 MCh 4 sulvanites, mixed-anion layered CuMCh(O,F), and 2D materials—and discuss computational predictions of potential new candidates in this family, highlighting their optical and electrical properties. Then, we finally review applications—for example, photovoltaic and photoelectrochemical solar cells, transistors, and light emitting diodes—that employ wide band gap chalcogenides as either an active or passive layer. Overall, by examining, categorizing, and discussing prospective directions in wide band gap chalcogenides, this Review aims to inspire continued research on this emerging class of transparent semiconductors and thereby enable future innovations for optoelectronic devices.

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

Rb 4 CuSb 2 Cl 11 and Rb 2 In 0.91(0.2) Sb 0.09 Cl 5 ·H 2 O: Wide Band Gap 0D Metal Halide Semiconductors

Herein, we report the discovery, structural and photophysical characterization of a new zero-dimensional (0D) lead-free all-inorganic halide, Rb 4 CuSb 2 Cl 11 , which adopts a new structure type. Single-crystal X-ray diffraction (SCXRD) shows that the structure consists of isolated, distorted seesaw [SbCl 4 ] − and trigonal planar [CuCl 3 ] 2− units, separated by Rb + cations that provide charge balance. Optoelectronic measurements and density functional theory (DFT) calculations indicate an indirect band gap of 2.89 eV, making it a candidate for wide-bandgap optoelectronic applications. Electrical resistivity was measured at 1.29 × 10 10 Ω·cm, and the trap-state density (n trap ) was found to be 7.44 × 10 10 cm −3 . Attempts to synthesize substitution analogs of Rb 4 CuSb 2 Cl 11 led to the synthesis of Rb 2 In 0.91(0.2) Sb 0.09 Cl 5 ·H 2 O, which was erroneously reported as Rb 2 SbCl 5 O in a previous study. Rb 2 In 0.91(0.2) Sb 0.09 Cl 5 ·H 2 O adopts a vacancyordered perovskite structure and exhibits broad-band yellow emission under UV excitation. The measured photoluminescence quantum yield (PLQY) for Rb 2 In 0.91 (0.2)Sb 0.09 Cl 5 ·H 2 O is 18.2%. These findings add to the growing class of quaternary metal halides with multiple cation and anion compositions, expanding the chemical phase space for the discovery of new materials with functional properties.

Crystal structure↗
DOE OSTI2019

Hybrid Charge-Transfer Semiconductors: (C 7 H 7 )SbI 4 , (C 7 H 7 )BiI 4 , and Their Halide Congeners

Hybrid metal halides yield highly desirable optoelectronic properties and offer significant opportunity due to their solution processability. This contribution reports a new series of hybrid semiconductors, (C 7 H 7 )MX 4 (M = Bi 3+ , Sb 3+ ; X = Cl – , Br – , I – ), that are composed of edge-sharing MX 6 chains separated in space by π-stacked tropylium (C 7 H 7 + ) cations; the inorganic chains resemble the connectivity of BiI 3 . The Bi 3+ compounds have blue-shifted optical absorptions relative to the Sb 3+ compounds that span the visible and near-IR region. Consistent with observations, DFT calculations reveal that the conduction band is composed of the tropylium cation and valence band primarily the inorganic chain: a charge-transfer semiconductor. The band gaps for both Bi 3+ and Sb 3+ compounds decrease systematically as a function of increasing halide size. Furthermore these compounds are a rare example of charge-transfer semiconductors that also exhibit efficient crystal packing of the organic cations, thus providing an opportunity to study how structural packing affects optoelectronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Advances in Singlet Fission Chromophore Design Enabled by Vibrational Spectroscopies

Singlet fission leads to the formation of two separate triplet T 1 excitons from an initial singlet S1 exciton through 1 (TT) and 1 (T...T), multiexcitonic intermediates that retain singlet character. Its ability to achieve external quantum efficiencies higher than 100% made it an attractive candidate for optoelectronic device applications. However, singlet fission has not been applied widely despite having been investigated by a myriad of spectroscopic methods, in part due to our poor understanding of how to optimize molecular structure and packing in chromophores well-suited to large-scale production. Vibrational spectroscopies provide a solution, because they directly probe nuclear motions, allowing us to monitor evolving structural changes in molecules undergoing singlet fission, thus providing us with roadmaps to design molecules suitable for optoelectronic applications. Furthermore, this Perspective reviews the contributions and analyzes the future directions of vibrational spectroscopies to the advancement in our knowledge about the mechanisms and rational designing of chromophores undergoing efficient singlet fission.

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

Photo-Induced Charge Transfer of Fullerene and Non-Fullerene Conjugated Polymer Blends via Ab Initio Excited-State Dynamics

Organic conjugated polymers (CPs) are promising candidates for organic photovoltaic (OPV) devices due to their unique tunable mechanical and optoelectronic performance. Over the last decade, optoelectronic properties of narrow band gap CPs as a blend with acceptor units are largely optimized, which leads to noticeable progress in OPV technology. However, their power conversion efficiency is still lower than their organic counterparts (i.e., silicon), limiting their practical usage. In this study, we employ ab initio molecular dynamics to explore photo-induced charge transfer (CT) of the diketopyrrolopyrrole-based polymer as a blend with non-fullerene (i.e., ITIC) and fullerene (i.e., PCBM) acceptor units. The results of charge carrier dynamics induced by selected photoexcitation show that hole density redistribution in space is much faster than electron relaxation. We track the relaxation rates of charge carriers over time, where the derivative of the difference between the rate of electron and hole implies the current density at zero voltage. Furthermore, this can be utilized to characterize the CT performance of CPs blended with different acceptor units. Relaxation rate results indicate that CP blend with ITIC promises a better PV performance, illustrating that the current computational approach opens the door to determine bulk heterojunctions’ electronic performance for OPV devices and narrowing down the list of potential donor–acceptor candidates.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Octahedral Distortion and Excitonic Behavior of Cs 3 Bi 2 Br 9 Halide Perovskite at Low Temperature

The metal halide ionic octahedron, represented as [MX 6 ] $n$- (M = metal cation, X = halide anion), serves as the basic structural unit in halide perovskites and plays a crucial role in determining their optoelectronic and chemical properties. Thus, it is possible to correlate the responses of metal halide perovskites to various environmental stimuli with the dynamic behaviors of the [MX 6 ] $n$- octahedra. In this study, with the temperature-dependent single-crystal X ray diffraction (SCXRD) measurements on Cs 3 Bi 2 Br 9 2D halide perovskites, we can identify two classes of distortions through the lowering of temperature: intraoctahedral distortion, which is the off-centering of Bi 3+ cation within a [BiBr 6 ] 3– octahedron due to the Bi 3+ 6s 2 lone pair electrons, and interoctahedral distortion, which is the collective misalignments among the [BiBr 6 ] 3– building blocks. Free exciton (FE) and self-trapped exciton (STE) models are used to study the relationship between the distortion of octahedra in Cs 3 Bi 2 Br 9 and the corresponding changes in its optoelectronic properties, which transform from dominating blue emission above 100 K to red emission at 4 K. In conclusion, this work provides new insights into the excitonic behaviors of perovskites and suggests a possibility that we can design and rationalize the optical properties of halide perovskites by regulating the environmental stimuli based on the knowledge of behaviors of the individual [MX 6 ] $n$- building blocks.

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

Side Chain Engineering of Near-IR Aza-BODIPY Dyes Enables Processable Films with High Hole Mobility in Diodes

Boron chelated azadipyrromethene (Aza-BODIPY) derivatives are promising candidates for near-infrared optoelectronic applications due to their tunable absorption, electron-deficient core, and strong π-conjugation. Here, in this work, we synthesized and studied a series of 1-naphthylethynyl-substituted aza-BODIPY molecules featuring hexyl or hexyloxy solubilizing groups at either the proximal or the distal phenyl positions. These substitutions were designed to improve the solubility, film formation, and optoelectronic properties. We found that solubilizing groups not only enabled uniform solution-processed films but also fine-tuned key properties, such as absorption onset, oxidation potential, and energy levels. Charge transport analysis showed consistently high hole mobilities (∼10 –3 cm 2 /V s) across all substituted derivatives when CuI was used as the hole transport layer, regardless of film morphology. In contrast, electron mobilities tended to be low and inconsistent, partly because of the relatively poor-quality films on the ZnO electron transport layer. Overall, we have shown that solubilizing groups enable film solution-casting and can fine-tune the properties of these near-infrared aza-BODIPY derivatives.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effects of thermochemical treatment on CuSbS 2 photovoltaic absorber quality and solar cell reproducibility

CuSbS 2 is a promising nontoxic and earth-abundant photovoltaic absorber that is chemically simpler than the widely studied Cu 2 ZnSnS 4 . However, CuSbS 2 photovoltaic (PV) devices currently have relatively low efficiency and poor reproducibility, often due to suboptimal material quality and insufficient optoelectronic properties. To address these issues, here we develop a thermochemical treatment (TT) for CuSbS 2 thin films, which consists of annealing in Sb 2 S 3 vapor followed by a selective KOH surface chemical etch. The annealed CuSbS 2 films show improved structural quality and optoelectronic properties, such as stronger band-edge photoluminescence and longer photoexcited carrier lifetime. These improvements also lead to more reproducible CuSbS 2 PV devices, with performance currently limited by a large cliff-type interface band offset with CdS contact. Altogether, these results point to the potential avenues to further increase the performance of CuSbS 2 thin film solar cell, and the findings can be transferred to other thin film photovoltaic technologies.

14 SOLAR ENERGY↗
DOE OSTI2026

Light-Driven Iodine Loss and Photoluminescence Homogenization in Mixed-Halide Perovskite Semiconductors

Carrier-induced instabilities in lead halide perovskites are often investigated as either transient phenomena, e.g., photoinduced halide segregation or permanent performance changes, e.g., photodegradation, while the mechanistic links between them remain unclear. Here, we aim to connect these observations by studying a model mixed-halide system, MAPb(Br x I 1–x ) 3 . By combining grazing-incidence X-ray diffraction, photothermal deflection spectroscopy, and photoluminescence measurements with hyperspectral microscopy, we investigate the role of mobile halide defects and local chemistry on reversible and long-term instabilities in these materials. Our results show that mixed-halide perovskites are uniquely susceptible to photoinduced changes with illumination driving initial iodide redistribution (i.e., halide segregation), eventual selective iodine expulsion, and subsequent changes in photoinduced halide segregation behavior. By quantifying structural and compositional changes, we estimate an approximately 3–5% iodine loss in our mixed-halide samples after only 24 h of illumination. Further, using microscale measurements, we identify pre-existing iodide-rich domains as key contributors to both the observed transient photostability and permanent iodine loss in MAPbBrI 2 , and see evidence that extended light soaking results in iodide redistribution that improves optoelectronic homogeneity. Overall, our results emphasize the importance of carrier-induced halide oxidation in creating a dynamic defect landscape in mixed-halide perovskites and provide a framework for interpreting apparent light-driven changes in optoelectronic behavior through the lens of permanent compositional changes.

electrical conductivity↗
DOE OSTI2018

First-Principles Investigation of Borophene as a Monolayer Transparent Conductor

Two-dimensional boron is promising as a tunable monolayer metal for nano-optoelectronics. We study the optoelectronic properties of two likely allotropes of two-dimensional boron, β12 and δ6, using first-principles density functional theory and many-body perturbation theory. We find that both systems are anisotropic metals, with strong energy- and thickness-dependent optical transparency and a weak (<1%) absorbance in the visible range. Additionally, using state-of-the-art methods for the description of the electron–phonon and electron–electron interactions, we show that the electrical conductivity is limited by electron–phonon interactions. Furthermore, our results indicate that both structures are suitable as a transparent electrode.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Pressure Impact on the Crystal Structure, Optical, and Transport Properties in Layered Oxychalcogenides BiCu Ch O( Ch = S, Se)

The layered oxychalcogenides BiCuChO (Ch = S, Se, Te) represent a unique family of two-dimensional semiconductors with extraordinary optoelectronic and thermoelectric properties. Chemical strategies such as elemental doping have been used to modify their crystal structures and electronic configurations for better photocatalytic performances. Herein, we report the pressure impact on the crystalline and electronic band structures of BiCuChO (Ch = S, Se) with in situ synchrotron X-ray diffraction, Raman spectroscopy, electric resistivity and photocurrent measurements, and first-principle calculations. Under pressure, the crystalline lattices shrink continuously without symmetry breaking, which enhances the crystal field splitting; on the other hand, the pressure-induced charge delocalization causes the band broadening. The competition between the crystal field and charge delocalization demonstrates an efficient tool for band gap engineering: the electrical conductivity is enhanced below 12 GPa and monotonically decreases up to 40 GPa. In addition, BiCuSeO exhibits considerable photocurrent up to ~40 GPa, which suggests its potential application in pressure-responsive optoelectrical devices. Lastly, the comprehensive studies of the pressure effect on the crystal structure and electronic properties in two-dimensional semiconductors provide and in-depth understanding for developing new optoelectronic materials under extreme conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Effect of Moisture on Dopant Segregation in Solid Hosts

Transition metal-doped semiconductor materials are extensively employed for light harvesting and photocatalytic applications owing to their increased light absorption and charge mobility. Here, spatial tailoring of the Ni dopant in TiO 2 nanostructures is performed by varying the secondary processing parameters to engineer the resulting optoelectronic properties for select applications. Specifically, the aging of the dried Ti sol and the resulting Ni segregation are observed to be moisture-driven phenomena based on the infrared and time-resolved UV–vis spectroscopy measurements. While X-ray diffraction and scanning transmission electron microscopy coupled with electron energy-loss spectroscopy characterizations show a clear difference in the crystal structures between pristine TiO 2 powders and phase-segregated NiO–TiO 2 , the thermogravimetric measurements reveal substitution of the ethoxy group by ambient moisture, resulting in the ejection of hydroxylated Ni clusters. Moreover, the doped system could be locked into a metastable state by rapidly annealing the amorphous powders. Lastly, the photocatalytic activity of these different TiO 2 :Ni 2+ (15 mol %) nanoparticles under AM 1.5G solar light highlights the relationship between the photocatalytic activity and the dopant position. This ability to spatially control dopants within highly doped materials allows for direct control of specific optoelectronic properties, paramount for photoelectrochemical devices.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Improved Crystalline Structure and Enhanced Photoluminescence of ZnO Nanolayers in B i2 Se 3 /ZnO Heterostructures

The Bi 2 Se 3 /ZnO heterostructure is a new combination of high- and low-band-gap nanomaterials that can be implemented for optoelectronic devices. The influence of the Bi 2 Se 3 substrate on crystallization of ZnO nanolayers and charge separation at the Bi 2 Se 3 /ZnO interface reflects these important parameters, which affect optical and electronic properties of the heterostructure. Despite a few studies on Bi 2 Se 3 /ZnO heterostructures, the mechanisms of enhanced optical properties and correlation between optical and structural properties in such heterostructures are not studied in detail. In the present paper, we report on structure and optical properties of ZnO nanolayers with different thicknesses (10–150 nm) deposited by atomic layer deposition on planar and nonplanar Bi 2 Se 3 nanostructured coatings. Crystallization of ZnO nanolayers grown on Bi 2 Se 3 and Si substrates was analyzed by X-ray diffraction and scanning and transmission electron microscopy methods. Enhancement of ZnO photoluminescence in Bi 2 Se 3 /ZnO heterostructures in comparison to the photoluminescence of ZnO nanolayers of the same thickness deposited on p-doped Si substrates was observed. Correlation between the structure and optical properties of ZnO nanolayers in Bi 2 Se 3 /ZnO heterostructures is analyzed. Three complementary mechanisms of enhancement of optical properties of ZnO in Bi 2 Se 3 /ZnO heterostructures, based on charge separation at the Bi 2 Se 3 /ZnO interface, improvement of ZnO crystalline structure, and surface-plasmon–photon coupling, are proposed. The Bi 2 Se 3 /ZnO heterostructure is a new combination of high- and low-band-gap nanomaterials that can be implemented for optoelectronic devices. The influence of the Bi 2 Se 3 substrate on crystallization of ZnO nanolayers and charge separation at the Bi 2 Se 3 /ZnO interface reflects these important parameters, which affect optical and electronic properties of the heterostructure. Despite a few studies on Bi 2 Se 3 /ZnO heterostructures, the mechanisms of enhanced optical properties and correlation between optical and structural properties in such heterostructures are not studied in detail. In the present paper, we report on structure and optical properties of ZnO nanolayers with different thicknesses (10–150 nm) deposited by atomic layer deposition on planar and nonplanar Bi 2 Se 3 nanostructured coatings. Crystallization of ZnO nanolayers grown on Bi 2 Se 3 and Si substrates was analyzed by X-ray diffraction and scanning and transmission electron microscopy methods. Enhancement of ZnO photoluminescence in Bi 2 Se 3 /ZnO heterostructures in comparison to the photoluminescence of ZnO nanolayers of the same thickness deposited on p-doped Si substrates was observed. Correlation between the structure and optical properties of ZnO nanolayers in Bi 2 Se 3 /ZnO heterostructures is analyzed. Finally, three complementary mechanisms of enhancement of optical properties of ZnO in Bi 2 Se 3 /ZnO heterostructures, based on charge separation at the Bi 2 Se 3 /ZnO interface, improvement of ZnO crystalline structure, and surface-plasmon–photon coupling, are proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Boosting Photoelectric Conductivity in Porphyrin-Based MOFs Incorporating C 60

Electronic structure calculations show that guest C60 in the porphyrin-containing metal organic frameworks Zn 2 (TCPB)(DA-ZnP) (DA-MOF; H 4 TCPB = 1,2,4,5-tetrakis(4-carboxyphenyl)benzene, DA-ZnP = [5,15-bis[(4-pyridyl)ethynyl]-10,20-diphenylporphinato]zinc(II)) and Zn 2 (TCPB)(F-ZnP) (F-MOF; F-ZnP = [5,15-di(4-pyridyl)-10,20-bis(pentafluorophenyl)porphinato]zinc(II)) engenders high photoelectrical conductivity due to efficient donor–acceptor charge-transfer (CT) interactions. Structural modifications at the meso position of the porphyrin influence the preferred positions of C 60 within the frameworks, giving rise to host–guest interactions with different anisotropic structural, electronic, and optoelectronic properties. A preferred slipped-parallel π-stacked interaction of C 60 that is predicted for NH 2 -substituted DA-MOF and F-MOF fosters strong CT transitions and lowers band gaps by ~1.0 eV compared to the pristine DA-MOF and F-MOF. Hopping rates computed using Marcus theory are found to be anisotropic and accelerated by multiple orders of magnitude across π-stacked interfaces created by C 60 incorporation, a consequence of strong electronic coupling between initial and final diabatic states. Calculations indicate that photoinduced electron transfer, as well as direct CT from porphyrin to C 60 upon irradiation, triggers a charge separation process that leads to the formation of what should be long-lived electron-trapped states at the heterojunctions. Lastly, design principles revealed here for the control of photophysical and electron-transfer processes will be useful for constructing new MOF-derived visible- and infrared-based optoelectronics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Magnetic-Field-Driven Electron Dynamics in Graphene

Graphene exhibits unique optoelectronic properties originating from the band structure at the Dirac points. It is an ideal model structure to study the electronic and optical properties under the influence of the applied magnetic field. In graphene, electric field, laser pulse, and voltage can create electron dynamics which is influenced by momentum dispersion. However, computational modeling of momentum-influenced electron dynamics under the applied magnetic field remains challenging. In this work, we perform computational modeling of the photoexcited electron dynamics achieved in graphene under an applied magnetic field. Our results show that magnetic field leads to local deviation from momentum conservation for charge carriers. With the increasing magnetic field, the delocalization of electron probability distribution increases and forms a cyclotron-like trajectory. Our work facilitates understanding of momentum resolved magnetic field effect on non-equilibrium properties of graphene, which is critical for optoelectronic and photovoltaic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗