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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Oxidatively Stable Nanoporous Silicon Photocathodes for Photoelectrochemical Hydrogen Evolution

Stable and high-performance nanoporous 'black silicon' photoelectrodes with electrolessly deposited Pt nanoparticle (NP) catalysts are made with two metal-assisted etching steps. Doubly etched samples exhibit >20 mA/cm2 photocurrent density at +0.2 V vs. reversible hydrogen electrode (RHE) for photoelectrochemical hydrogen evolution under 1 sun illumination. We find that the photocurrent onset voltage of black Si photocathodes prepared from single-crystal planar Si wafers increases in oxidative environments (e.g., aqueous electrolyte) owing to a positive flat-band potential shift caused by surface oxidation. However, this beneficial oxide layer becomes a kinetic barrier to proton reduction that inhibits hydrogen production after just 24 h. To mitigate this problem, we developed a novel second Pt-assisted etch process that buries the Pt NPs deeper into the nanoporous Si surface. This second etch shifts the onset voltage positively, from +0.25 V to +0.4 V vs. RHE, and reduces the charge-transfer resistance with no performance decrease seen for at least two months.

08 HYDROGEN↗
DOE OSTI2011

Fabrication and photocatalytic activity of high-efficiency visible-light-responsive photocatalyst ZnTe/TiO{sub 2} nanotube arrays

A new ZnTe modified TiO{sub 2} nanotube (NT) array catalyst was prepared by pulse potential electrodeposition of ZnTe nanoparticles (NPs) onto TiO{sub 2} NT arrays, and its application for photocatalytic degradation of anthracene-9-carboxylic acid (9-AnCOOH) was investigated. The even distribution of ZnTe NPs was well-proportionately grown on the top surface of the TiO{sub 2} NT while without clogging the tube entrances. Compared with the unmodified TiO{sub 2} NT, the ZnTe modified TiO{sub 2} NT (ZnTe/TiO{sub 2} NT) showed significantly enhanced photocatalytic activity towards 9-AnCOOH under simulated solar light. After 70 min of irradiation, 9-AnCOOH was degraded with the removal ratio of 45% on the bare TiO{sub 2} NT, much lower than 80%, 90%, and 100% on the ZnTe/TiO{sub 2} NT with the ZnTe NPs prepared under the pulsed 'on' potentials of -0.8, -1.0, and -2.0 V, respectively. The increased photodegradation efficiency mainly results from the improved photocurrent density as results of enhanced visible-light absorption and decreased hole-electron recombination due to the presence of narrow-band-gap p-type semiconductor ZnTe. -- Graphical abstract: Surface-view SEM images of ZnTe/TiO{sub 2} NT prepared under -2.0 V, and the inset is the corresponding enlarged drawings. Display Omitted Research highlights: {yields} A new method to deposit chalcogenides of transition metals on the TiO{sub 2} nanotubes. {yields} The even distribution of ZnTe nanoparticles was well-proportionedly grown onto TiO{sub 2} NT arrays. {yields} ZnTe/TiO{sub 2} NT showed remarkably increased photocurrent density. {yields} ZnTe/TiO{sub 2} NT showed good photocatalytic performance. {yields} The prepared new catalyst has a promising application in practical systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2026

Experimental Evidence of Free Carrier Generation in 2D Hybrid Organic–Inorganic Perovskites

Despite the significant potential of 2D hybrid organic–inorganic perovskites (2DHOIPs) for high-efficiency optoelectronics application-comparable to their 3D counterparts, the fundamental carrier photogeneration remains unclear. In contrast to conventional ultrafast optical property characterization, we use ultrafast photocurrent spectroscopy to investigate the early-time electrical properties of type-I and type-II 2DHOIPs by manipulating the quantum confinement and the dielectric quantum matching effect. We discovered that the high frequency dielectric quantum matching effect plays a major role in 2DHOIPs, demonstrated by their high carrier mobility (µ), near-unity photogeneration quantum yield (Φ), below-room temperature exciton binding energy (E b ), and approaching 3D space factor (DSF). Our work shows that the optoelectronic performances of 2DHOIPs are comparable to their counterparts of 3DHOIPs.

2D perovskite↗
DOE OSTI2024

Comprehensive Study of Carrier Recombination in High‐Efficiency CdTe Solar Cells Using Transient Photovoltage

Cadmium telluride (CdTe) solar cells represent a commercially successful photovoltaic technology, with an annual production capacity approaching 20 GW. However, improving the open-circuit voltage (V OC ) remains challenging. This study aims to deepen the understanding of charge carrier recombination in CdTe solar cells and to explore alternative dynamical characterization methods that address the limitations found in conventionally used time-resolved photoluminescence for CdTe solar cells. Transient photovoltage and transient photocurrent techniques are utilized to investigate charge carrier dynamics under conditions resembling real-world solar cell operation. The results reveal that an effective nonradiative recombination lifetime of 580 ns dominates the charge dynamics at VOC values below 850 mV. Above this threshold, radiative recombination becomes significant, with a radiative recombination coefficient of 1.1 × 10 −9 cm 3 s −1 . Additionally, the stationary charge carrier density at 1 sun is determined to be around 1 × 10 14 cm −3 . By accurately determining both radiative and nonradiative recombination, this work provides a comprehensive understanding of carrier dynamics in high-performing CdTe devices and paves the way for improving the V OC and performance of CdTe solar cells.

CdTe solar cells↗
DOE OSTI2018

Photoelectric Properties of Film Composites Based on Poly(Vinyl Butyral) and Heterometallic Complexes

Photosensitive polymeric film composites based on nonphotoconducting poly(vinyl butyral) doped with heterometallic Cu/M complexes (M = Ca, Sr) were synthesized and investigated. These composites possessed photoconducting and photovoltaic properties and electron-type photoconductivity. The greater photocurrent for composites with complexes having shorter distances between the nearest Cu metal centers was attributed to the greater probability of electron transfer between these centers.

14 SOLAR ENERGY↗
DOE OSTI2019

Characterizations of 2-(pyranoquinolin-4-yl) malononitrile/p-silicon heterojunction

Thin film of 2-(pyranoquinolin-4-yl) malononitrile, PQM, was deposited on p-Si to fabricate a heterojunction of PQM/Si. Current–voltage characteristics for PQM/p-Si were investigated as a function of temperature. The diode ideality factor was calculated at different temperatures. The mechanisms for current transport in forward and reverse bias were deduced. At low voltage, the thermionic emission is the predominant mechanism of charge transport in PQM/p-Si. While ohmic conduction was observed at the higher voltage in PQM/p-Si. The photovoltaic performance for PQM/p-Si under illumination was studied and the parameters of short circuit photocurrent I{sub SC}, open-circuit photovoltage V{sub oc} and fill factor FF were calculated.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Special Features of the Optical Absorption and Photoconductivity of Indium Monoselenide Upon Laser Excitation

The successive ionic layer adsorption and reaction (SILAR) method is used to prepare InSe thin films and InSe nanoparticles. Shapes and sizes of the obtained nanoparticles are investigated using a scanning electron microscope and an atomic force microscope. The main parameters of the examined structures, nanoparticle sizes (4–20 nm), and band gap (Е{sub g} = 1.60 eV) for nanoparticles with the least sizes are determined. Superfast (1.5·10{sup -8} s) photocurrent relaxation and stimulated emission with line half-width of 8 Å have been observed upon exposure to laser radiation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Answering old questions with new techniques: Understanding performance-limiting factors in transition metal dichalcogenide photoelectrochemical solar cells

In the late 1970s and early 1980s, several research groups reported high-efficiency and stable photoelectrochemical solar cells based on transition metal dichalcogenides (TMDS; e.g., MoS 2 , WSe 2 , and MoSe 2 ) immersed in iodide/tri-iodide electrolytes. A consensus emerged that smooth crystals were necessary for high efficiency based on significant evidence that rough crystals with exposed edge sites produced lower photocurrents and fill factors. However, anecdotal observations in the literature hinted at significant performance variation among apparently smooth crystals with the possibility of highly active “hot” edge sites. Furthermore, this mini-review article is a case study on how spatially resolved photoelectrochemical techniques developed in the 2020s are answering old questions regarding the origin of performance variation in high efficiency n-type TMD|I – ,I 3 – |Pt photoelectrochemical solar cells.

14 SOLAR ENERGY↗
DOE OSTI2014

Non-toxic silver iodide (AgI) quantum dots sensitized solar cells

Highlights: • We have demonstrated AgI sensitized solar cell for the first time. • Obtained mesoporous titania powders possessed small crystallite size, high purity and surface area, and developed mesopores with a narrow pore size distribution. • Photovoltaic measurements revealed the electron injection from AgI to TiO{sub 2}. • The assembled AgI-QD solar cells yielded a power conversion efficiency of 0.64% under one sun illumination. • AgI may be a suitable candidate material for use as a non-toxic sensitizer in QDSSC. - Abstract: The present study reports the performance of a new photosensitizer -AgI quantum dots (QDs)- and mesoporous titania (TiO{sub 2}) nanocrystals synthesized by sol–gel (SG) method for solar cells. Furthermore, the effects of n-heptane on the textural properties of TiO{sub 2} nanocrystals were comprehensively investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N{sub 2} adsorption–desorption measurements, and UV–vis spectroscopy. TiO{sub 2} powders exhibited an anatase-type mesoporous structure with a high surface area of 89.7 m{sup 2}/g. Afterwards, the QDs were grown on mesoporous TiO{sub 2} surface to fabricate a TiO{sub 2}/AgI electrode by a successive ionic layer adsorption and reaction (SILAR) deposition route. Current–voltage characteristics and electrochemical impedance spectroscopy (EIS) data demonstrated that the injection of photoexcited electrons from AgI QDs into the TiO{sub 2} matrix produces photocurrents. The assembled AgI-QD solar cells yielded a power conversion efficiency of 0.64% and a short-circuit current of 2.13 mA/cm{sup 2} under one sun illumination.

36 MATERIALS SCIENCE↗
DOE OSTI2015

UV light-assisted fabrication of Cu{sub 0.91}In{sub 0.09}S microspheres sensitized TiO{sub 2} nanotube arrays and their photoelectrochemical properties

Highlights: • Cu{sub 0.91}In{sub 0.09}S microspheres were deposited on TiO{sub 2} NTs by a photodeposition method. • The average diameter of Cu{sub 0.91}In{sub 0.09}S microspheres is 600 nm. • The TiO{sub 2} NTs/CIS shows high photocurrents and visible photocatalytic activity. - Abstract: TiO{sub 2} nanotube arrays sensitized with Cu{sub 0.91}In{sub 0.09}S microspheres (TiO{sub 2} NTs/CIS) were successfully fabricated by a two-step process of anodization and followed by an in situ photodeposition method. The structural investigation by scanning electron microscopy and transmission electron microscopy indicated that the Cu{sub 0.91}In{sub 0.09}S microspheres with average diameter of 600 nm grew on the surface of the TiO{sub 2} nanotubes. The TiO{sub 2} NTs/CIS exhibited more excellent photoelectrochemical properties and photocatalytic activities than those of TiO{sub 2} NTs under visible light irradiation, and the corresponding electron transformation was proposed in detail.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Fabrication and characterization of metal–semiconductor–metal ultraviolet photodetector based on rutile TiO{sub 2} nanorod

The fabrication and characterization of a metal–semiconductor–metal ultraviolet photodetector are studied. The photodetector is based on TiO{sub 2} nanorods (NRs) grown on p-type (1 1 1)-oriented silicon substrate seeded with a TiO{sub 2} layer is synthesized by radio frequency reactive magnetron sputtering. A chemical bath deposition is used to grow TiO{sub 2} NRs on Si substrate. The structural and optical properties of the obtained sample are analyzed by using X-ray diffraction and field emission-scanning electron microscopy. Results show a tetragonal rutile structure of the synthesized TiO{sub 2} NRs. Optical properties are further examined using photoluminescence spectroscopy. A sharp and high-intensity UV peak at 367 nm is observed in comparison with visible defect peaks centered at 432 and 718 nm. Upon exposure to 365 nm light (2.3 mW/cm) at 5 V bias, the device displays 76.06 × 10{sup 2} sensitivity, internal photodetector gain of 77.06, photocurrent of the device is 2.62 × 10{sup −5} A and photoresponse peak of 69.7 mA/W. The response and recovery times are calculated as 18.5 and 19.1 ms upon illumination to a pulse UV light (365 nm, 2.3 mW/cm{sup 2}) at 5 V applied bias. These results demonstrate that the fabricated high-quality photodiode is a promising candidate as a low-cost UV photodetector for commercially-integrated photoelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Enhancing visible light photocatalytic and photocharge separation of (BiO){sub 2}CO{sub 3} plate via dramatic I{sup −} ions doping effect

Highlights: • Novel I-(BiO){sub 2}CO{sub 3} was prepared by a facile chemical precipitation method. • I{sup −} ions impurity level located on the top of valence band of (BiO){sub 2}CO{sub 3}. • I{sup −} ions doping largely improved photocatalytic activity of I-(BiO){sub 2}CO{sub 3}. • I-(BiO){sub 2}CO{sub 3} displayed excellent photocharge separation efficiency. - Abstract: Novel I{sup −} ions doped (BiO){sub 2}CO{sub 3} (I-(BiO){sub 2}CO{sub 3}) photocatalysts were successfully synthesized via a facile chemical precipitation method. Under visible light (λ > 400 nm), I-(BiO){sub 2}CO{sub 3} displayed much higher activity for rhodamine B and dichlorophenol degradation than the undoped (BiO){sub 2}CO{sub 3}. The pseudo-first-order rate constant k{sub app} of RhB degradation over 15.0% I-(BiO){sub 2}CO{sub 3} was 0.54 h{sup −1}, which is 11.3 times higher than that of (BiO){sub 2}CO{sub 3}. The doped I{sup −} ions formed an impurity level on the top of valence band of (BiO){sub 2}CO{sub 3} and induced much more visible light to be absorbed. The enhanced photocurrent and surface photovoltage properties were detected, which strongly ensures the efficient separation of electrons and holes in I-(BiO){sub 2}CO{sub 3} system under visible light. It provides a facile way to improve the photocatalytic activity of the wide-band-gap (BiO){sub 2}CO{sub 3} via intense doping effect of I{sup −} ions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A new method for the fabrication of a bilayer WO3/Fe2O3 photoelectrode for enhanced photoelectrochemical performance

Highlights: • A thin layer of Fe{sub 2}O{sub 3} is layered on the electrodeposited WO{sub 3} photoelectrode. • The light absorption of WO{sub 3} was extended towards the visible light region, resulting higher photoelctrochemical performance. • Charge transfer mechanism in the bilayer photoanode was suggested. - Abstract: A bilayer WO{sub 3}/Fe{sub 2}O{sub 3} heterojunction photoelectrode was prepared with a new approach for photoelectrochemical reactions. WO{sub 3} was deposited onto an FTO conductive glass substrate via electrodeposition, followed by the deposition of an ultrathin Fe{sub 2}O{sub 3} layer using the chemical bath deposition method. The presence of Fe{sub 2}O{sub 3} layer improved the light absorption of WO{sub 3}/Fe{sub 2}O{sub 3} toward visible light region (red-shift). The addition of a thin layer of Fe{sub 2}O{sub 3} on WO{sub 3} resulted in higher photocatalytic performance (two-fold improvement) compared to that of pristine WO{sub 3}. In addition, the WO{sub 3}/Fe{sub 2}O{sub 3} photoelectrode also showed a positive photoresponse for methanol degradation. The photocurrent generation of the bilayer photoelectrode improved 1.6-fold with the addition of methanol as a sacrificial donor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Al3+ doping into TiO2 photoanodes improved the performances of amine anchored CdS quantum dot sensitized solar cells

Highlights: • Several Al{sup 3+}-doped TiO{sub 2} nanocomposites were applied as photoanodes of CdS QDSSCs. • The cells were sensitized using ethylglycinate hydrochloride (amine)-capped CdS QDs. • The highest efficiency was measured for the cell containing 0.3% Al and 8.25% amine. • The electron life time was the most improved in the optimized cell (τ{sub e} = 37.58 ms). • The optimized cell showed η = 2.40%, V{sub OC} = 0.584 V, FF = 0.361 and J{sub SC} = 11.38 mA cm{sup −2}. - Abstract: Some quantum dot-sensitized solar cells (QDSSCs) were fabricated by doping Al{sup 3+} ions into the TiO{sub 2} and addition of amine (ethylglycinate hydrochloride) to the CdS solution in order to improve their efficiency. Results indicated that the photovoltaic parameters of the optimized cell were boosted compared with those of the reference cell which was free of Al{sup 3+} QDs and amine indicating 68, 73 and 10.40% improvements in efficiency, current density and open-circuit voltage, respectively. The electrochemical impedance spectra (EIS) proved that the electron life time was the most improved by 1.60 times in the optimized cell (τ{sub e} = 37.58 ms) compared with that of the cell made only using pure TiO{sub 2} (τ{sub e} = 23.52 ms). Thus, addition of 0.3%wt Al{sup 3+} as a dopant was appropriate to attain suitable photocurrent efficiency for the QDSSCs because it could be used in a minimum amount to improve the electron transport, drop the recombination and increase the cell efficiency.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Self-assembly synthesis of BiVO4/Polydopamine/g-C3N4 with enhanced visible light photocatalytic performance

Highlights: • BiVO{sub 4}/PDA/g-C{sub 3}N{sub 4} was synthesized via simple self-assembly at the room temperature. • PDA has a strong binding affinity to BiVO{sub 4} and g-C{sub 3}N{sub 4} to form BiVO{sub 4}/PDA/g-C{sub 3}N{sub 4}. • BiVO{sub 4}/PDA/g-C{sub 3}N{sub 4} exhibits good stability and reusability in the photocatalytic reaction of glyphosate. • The enhanced activity of BiVO{sub 4}/PDA/g-C{sub 3}N{sub 4} is mainly attributed to the increased charge separation. - Abstract: BiVO{sub 4}/PDA(Polydopamine)/g-C{sub 3}N{sub 4} was synthesized by facile ultrasonic dispersion and self-assembly at the room temperature, and monoclinic BiVO{sub 4} was embedded on PDA/g-C{sub 3}N{sub 4} sheet, which PDA was first formed in situ on the surface of g-C{sub 3}N{sub 4} via self-polymerization of dopamine. The dependence of photocatalytic activity on the structural, electronic and optical properties of the BiVO{sub 4}/PDA/g-C{sub 3}N{sub 4} nanostructure has been explored using XRD, XPS, TEM, SEM, DRS, PL, BET and photocurrent. The BiVO{sub 4}/PDA/g-C{sub 3}N{sub 4} photocatalysts show higher activity of glyphosate degradation than BiVO{sub 4}, g-C{sub 3}N{sub 4} and BiVO{sub 4}/g-C{sub 3}N{sub 4} under visible light irradiation. The enhanced activity of BiVO{sub 4}/PDA/g-C{sub 3}N{sub 4} can be significantly attributed to the improved visible light absorption, enhanced specific surface area and increased charge separation. PDA has a strong and irreversible binding ability onto BiVO{sub 4} and g-C{sub 3}N{sub 4} to form BiVO{sub 4}/PDA/g-C{sub 3}N{sub 4}. This simple method at the room temperature is promising for the synthesis of high performance composite photocatalysts for different applications, such as pollutant degradation, photocatalytic splitting water, etc.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Screen printing large-area organometal halide perovskite thin films for efficient photodetectors

Highlights: • A stable paste with perovskite precursor was produced out. • Screen printing was proposed to fabricate perovskite thin films. • The perovskite photodetectors with symmetric architectures show reasonable performance with high photocurrent and fast response. - Abstract: Organometal halide perovskites have demonstrated excellent features compared to conventional optoelectronic materials. To date, the perovskite films have generally been fabricated by either spin coating or vapor deposition. However, both methods cannot simultaneously meet large scale and low cost of production. Here, a simple, low-cost and high-throughput strategy was proposed to fabricate perovskite thin films, which were further applied in photodetectors. First, lead compound nanoparticles were synthesized by a solvent precipitation method, then a paste with the lead compound nanoparticles was screen printed to form PbO films involving calcination, and next the PbO films directly reacted with CH{sub 3}NH{sub 3}I solution to convert into CH{sub 3}NH{sub 3}PbI{sub 3} films. The CH{sub 3}NH{sub 3}PbI{sub 3} films consisted of micron crystals, whose sizes can be effectively controlled by adjusting CH{sub 3}NH{sub 3}I concentration. Furthermore, the CH{sub 3}NH{sub 3}PbI{sub 3} films were applied in photodetectors, which showed good performance with high sensitivity and fast response.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Low cost and solution processible sandwiched CH3NH3PbI3-xClx based photodetector

Highlights: • High quality CH{sub 3}NH{sub 3}PbI{sub 3-x}Cl{sub x} thin film is synthesized using low temperature solution processible spin coating technique. • Perovskite based Metal-semiconductor-metal (MSM) photodetector is demonstrated without hole or electron transporting materials or noble metals. • Low cost & simple structured perovskite device exhibits good transient response, responsivity and detectivity. - Abstract: The CH{sub 3}NH{sub 3}PbI{sub 3-x}Cl{sub x} has been emerged as one of the most promising materials for the photodetector based applications. In recent years, many device structures consisting of hole transporting material, electron transporting material, conducting polymers and noble metals as contact electrodes have been investigated which escort to the increased cost and complexity in the fabrication process. Hence, it is essential to explore low cost, simple processed and high-performance photodetectors. The effect of applied external bias on photodetector has been examined in order to investigate performance. It is important to mention that because of the ion migration phenomenon taking place across the junction at higher bias, an unsaturated photocurrent has been observed during ON time of the photoresponse which may be scope of study for furtherance in low cost and highly stable photodetector. Responsivity and detectivity has been increased by 40 and 32 times at 1.2 V. Similarly, LDR is increased by 8 times.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Anisotropic ionic transportation performances of (100) and (112) planes in MAPbI3 single crystal

Highlights: • Anisotropic ion transportations of MAPbI{sub 3} are studied. • Photon excited ion transportation is investigated. • Linear increase trends with incident light power of ion transportation are observed. • Enhanced electron and ion transportations have been observed on (112) plane of MAPbI{sub 3}. • (112) plane of MAPbI{sub 3} shows more active transportation properties than (100). - Abstract: Organic–Inorganic hybrid perovskites attract intensive attentions due to significant optoelectronic performances. However, abnormal phenomena such as photocurrent hysteresis and slow photoconductivity response caused by ion migration made ionic transportation properties to be a hot topic in this area. Thinking of serious influences such as efficiency decay of excited carrier separation and poor reliability are caused by ion migration, systematical research on this topic is still highly demanded. Here, anisotropic ionic transportation performances of (100) and (112) planes in MAPbI{sub 3} single crystal have been investigated with various photon excitation conditions. Enhanced ionic conductance had been extracted on (112) plane both with and without illuminations. Comparing to exponential saturation revealed by the electrons, the ionic conductance exhibits a linear increase trends with incident light power in MAPbI{sub 3}.

36 MATERIALS SCIENCE↗