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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Indigo-Based Acceptor Type Small Molecules: Synthesis, Electrochemical and Optoelectronic Characterizations

In this paper, we report design and synthesis of novel low bandgap small molecules, indigo-benzimidazole (Tyr-3) and indigo-schiff base (Tyr-4) type acceptors. In these structures, tert-butoxycarbonyl (t-BOC) group has been attached to indigo nitrogen atom in order to increase the solubility. UV-vis absorption spectra of Tyr-3 and Tyr-4 dyes exhibit wide absorption bands ranging from 350 to 600 nm, indicating the relatively low bandgap giving around 2.07 eV for each. Excitation of both Tyr-3 and Tyr-4 dyes at 485 nm displays characteristic emission features of indigo moiety and also intramolecular charge transfer complex (ICT) related with their subunits. Besides increasing fluorescence quantum yields as compared to model compound, biexponential decay times for fluorescence life times were also obtained for Tyr-3 and Tyr-4 dyes. Their appropriate energy levels along with low HOMO levels are desired for light harvesting acceptors for organic solar cells when blended with poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2′,1′,3′-benzothiadiazole] (PCDTBT) as donor polymer. Photovoltaic behavior of the synthesized dyes were examined in bulk heterojunction concept and achieved photovoltaic conversion efficiencies were discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

A noticeable effect of novel Nd{sup 3+} doping on physical properties of nebulizer spray deposited AZO thin films for optoelectronic technology

In this work, neodymium (Nd) doped aluminum zinc oxide (Nd:AZO) films are prepared on glass substrates via simple spray nebulizer method for the first time. The different Nd doping concentrations were taken as 0%, 0.5%, 1% and 1.5 wt%, however, Al concentration was kept constant as 3 wt%. From X-ray diffraction (XRD) data, various structural properties like: crystallite size, microstrain, dislocation density, lattice constants and texture coefficient were investigated. XRD study confirmed that the Al and Nd were incorporated into ZnO. All the deposited films are of polycrystalline nature and hexagonal structure with (002) orientation. The topology studied by AFM showed that the film had low surface roughness and its values were slightly increased from 21 to 37 nm. Elemental mapping and EDAX studies confirmed the occurrence of Zn, O, Al and Nd in prepared Nd:AZO film. Transmission of deposited Nd:AZO film is around 92% in visible spectrum and estimated energy gap is ~ 3.31 eV. PL spectrum emitted one strong NBE emission at ~ 386 nm for all films, signify their better optical quality. Electrical parameters were studied by four probe measurement and low resistivity (ρ) i.e. ~ 4.12 × 10{sup −4} Ω cm and high carrier concentrations (n) i.e. ~ 3.96 × 10{sup 21} cm{sup −3} were observed for 1.5 wt% Nd:AZO films. The calculated value of ϕ is large as 14.33 × 10{sup −3} (Ω/sq){sup −1}, which are enough for an opto-electronic application.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Controlled Growth of Ordered III-Nitride Core-Shell Nanostructure Arrays for Visible Optoelectronic Devices

In our paper, we demonstrate the growth of ordered arrays of nonpolar {101 ¯ 0} core–shell nanowalls and semipolar {101 ¯ 1} core–shell pyramidal nanostripes on c-plane (0001) sapphire substrates using selective-area epitaxy and metal organic chemical vapor deposition. The nanostructure arrays are controllably patterned into LED mesa regions, demonstrating a technique to impart secondary lithography features into the arrays. Moreover, we study the dependence of the nanostructure cores on the epitaxial growth conditions and show that the geometry and morphology are strongly influenced by growth temperature, V/III ratio, and pulse interruption time. We also demonstrate the growth of InGaN quantum well shells on the nanostructures and characterize the structures by using micro-photoluminescence and cross-section scanning tunneling electron microscopy.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Effect of ZnSe/GaAs interface treatment in ZnSe quality control for optoelectronic device applications

Here, we investigate the role of interface initiation conditions on the growth of ZnSe/GaAs heterovalent heterostructures. ZnSe epilayers were grown on a GaAs surface with various degrees of As-termination and the application of either a Zn or Se pre-treatment. Structural analysis revealed that Zn pre-treatment of an As-rich GaAs surface suppresses Ga 2 Se 3 formation at the interface and promotes the growth of high crystal quality ZnSe. This is confirmed with low-temperature photoluminescence. However, moderation of Ga-Se bonding through a Se pre-treatment of an As-rich GaAs surface can prevent excessive intermixing at the interface and promote excitonic emission in the underlying GaAs layer. These results provide guidance on how best to prepare heterovalent interfaces for various applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The electronic structure of the antimony chalcogenide series: Prospects for optoelectronic applications

In this study, density functional theory is used to evaluate the electronic structure of the antimony chalcogenide series. Analysis of the electronic density of states and charge density shows that asymmetric density, or ‘lone pairs’, forms on the Sb{sup III} cations in the distorted oxide, sulphide and selenide materials. The asymmetric density progressively weakens down the series, due to the increase in energy of valence p states from O to Te, and is absent for Sb{sub 2}Te{sub 3}. The fundamental and optical band gaps were calculated and Sb{sub 2}O{sub 3}, Sb{sub 2}S{sub 3} and Sb{sub 2}Se{sub 3} have indirect band gaps, while Sb{sub 2}Te{sub 3} was calculated to have a direct band gap at Γ. The band gaps are also seen to reduce from Sb{sub 2}O{sub 3} to Sb{sub 2}Te{sub 3}. The optical band gap for Sb{sub 2}O{sub 3} makes it a candidate as a transparent conducting oxide, while Sb{sub 2}S{sub 3} and Sb{sub 2}Se{sub 3} have suitable band gaps for thin film solar cell absorbers. - Graphical abstract: A schematic illustrating the interaction between the Sb{sup III} cations and the chalcogenide anions and the change in their respective energy levels down the series. - Highlights: • The electronic structure of the antimony chalcogenide series is modelled using DFT. • Asymmetric density is present on distorted systems and absent on the symmetric telluride system. • Asymmetric density is formed from the mixing of Sb 5s and anion p states, where the anti-bonding combination is stabilised by the Sb 5p states. • The asymmetric density weakens down the series due to the increase in energy of chalcogenide p states. • The increase in energy of the anion p states reduces the fundamental and optical band gaps.

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

Successful synthesis of single scheelite-structured CdW{sub 1-x}Mo{sub x}O{sub 4} continuous solid-solution and its composition-dependent optoelectronic properties

Highlights: • Scheelite structure CdW{sub 1-x}Mo{sub x}O{sub 4} solid-solution was prepared for the first time. • Lattice expanded while band gap narrowed with the substitution of W{sup 6+} by Mo{sup 6+}. • Luminescent and dielectric properties of the solid solution varied with composition. - Abstract: Rational design and construction of metastable structured materials is more and more attractive toward realizing novel functional devices. In this work, the synthesis of metastable scheelite-type CdW{sub 1-x}Mo{sub x}O{sub 4} solid solution in the entire compositional range (0 ≤ x ≤ 1) was achieved for the first time. XRD, FT-IR and Raman spectroscopies confirmed that all the solvothermal prepared samples were pure tetragonal scheelite structure without wolframite phase. Structural refinement data revealed a lattice expansion with the substitution of W{sup 6+} by Mo{sup 6+} ions. UV–Vis diffuse reflectance spectra indicated that band gap energy of the solid solutions reduced with the replacement of W{sup 6+} by Mo{sup 6+} ions. Moreover, SEM analyses found that morphologies of the solid solution changed with the compositions. Meanwhile, the influences of chemical composition on the photoluminescent and electrical properties of the scheelite-type CdW{sub 1-x}Mo{sub x}O{sub 4} solid solution were also investigated. The reported synthetic strategy may applied to other metastable structures while the results reported will help to understand the structure and structure-property relations of scheelite-type ABO{sub 4} compounds.

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

Growth, structural and optoelectronic properties tuning of nitrogen-doped ZnO thin films synthesized by means of reactive pulsed laser deposition

Highlights: • PLD technique has been used to elaborate N doped ZnO. • A maximum incorporation of 0.7 at.% has been achieved at a pressure of 25 mTorr. • Increasing the N{sub 2} pressure decreases the nitrogen content with the creation of more defects. • Optical transmission and PL spectra have confirmed the band gap narrowing. - Abstract: Pulsed laser deposition has been successfully used to achieve in-situ nitrogen doping of zinc oxide thin films at a temperature as low as 300 °C. Nitrogen-doped zinc oxide (ZnO:N) thin films with a maximum nitrogen content of 0.7 at.% were obtained by varying the nitrogen background pressure in the range of 0–150 mTorr. The ZnO:N thin films were found to present hexagonal crystalline structure with dense and smooth surface. X-ray photoelectron spectroscopy analysis confirms the effective incorporation of nitrogen into ZnO thin films. Optical transmission together with room temperature photoluminescence measurements show that the band gap of the ZnO:N films shifts from 3.3 eV to 3.1 eV as nitrogen concentration varies in the range of 0.2–0.7 at.%. The narrower band gap is obtained at an optimal nitrogen concentration of 0.22 at.%. This band gap narrowing is found to be caused by both nitrogen incorporation and nitrogen-induced defects in the ZnO:N films.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Revealing the optoelectronic and thermoelectric properties of the Zintl quaternary arsenides ACdGeAs{sub 2} (A = K, Rb)

Highlights: • Zintl tetragonal phase ACdGeAs{sub 2} (A = K, Rb) are chalcopyrite and semiconductors. • Their direct band gap is suitable for PV, optolectronic and thermoelectric applications. • Combination of DFT and Boltzmann transport theory is employed. • The present arsenides are found to be covalent materials. - Abstract: Chalcopyrite semiconductors have attracted much attention due to their potential implications in photovoltaic and thermoelectric applications. First principle calculations were performed to investigate the electronic, optical and thermoelectric properties of the Zintl tetragonal phase ACdGeAs{sub 2} (A = K, Rb) using the full potential linear augmented plane wave method and the Engle–Vosko GGA (EV–GGA) approximation. The present compounds are found semiconductors with direct band gap and covalent bonding character. The optical transitions are investigated via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity and energy-loss spectrum. Combining results from DFT and Boltzmann transport theory, we reported the thermoelectric properties such as the Seebeck’s coefficient, electrical and thermal conductivity, figure of merit and power factor as function of temperatures. The present chalcopyrite Zintl quaternary arsenides deserve to be explored for their potential applications as thermoelectric materials and for photovoltaic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

New anthracene-based-phtalocyanine semi-conducting materials: Synthesis and optoelectronic properties

Highlights: • Synthesis of tow phtalocyanines based on the anthracene and tetrazole. • Semi-conducting supramolecular material. • Good PL quantum yield. • The film morphology of the phtalocynine containing tetrazole group enhanced the carrier mobility. - Abstract: A new anthracene-based semi-conducting phtalocyanines AnPc and AnPc-Tr were synthesized in solvent-free conditions. The supramolecular structure of these compounds was confirmed by NMR and FT-IR spectroscopies. Their optical properties were investigated by UV–vis and photoluminescence spectroscopies. The optical gaps were estimated from the absorption-onsets films, and the obtained values were of 1.50 eV and 1.47 eV for AnPc-Tr and AnPc respectively. In solid state, a weaker π–π-interactions of conjugated systems were obtained in the case of AnPc-Tr in comparison with AnPc. This behavior was explained by steric hindrance of triazol groups, which decrease the planarity of macromolecular structure. The HOMO and LUMO levels were estimated using cyclic voltammetry analysis; two phtalocyanine derivatives show a comparable ionization potential. The phtalacyanine containing triazole groups (AnPc-Tr) reveals a higher electron affinity in comparison with AnPc. Single-layer diode devices were fabricated and showed relatively low turn-on voltages.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Optoelectronic and material properties of solution-processed Earth-abundant Cu 2 BaSn(S, Se) 4 films for solar cell applications

Copper barium thioselenostannate, Cu 2 BaSnS 4-x Se x (CBTSSe), absorbers employ low-toxicity and abundant metals while offering low-cost manufacturing options, controllable stoichiometry and band gap tunability (from 2 eV at x = 0 to 1.55 eV at x = 3). CBTSSe can therefore be considered a prospective candidate for maintaining or improving upon the advantages of already commercialized Cu(In,Ga)(S,Se) 2 (CIGSSe) and CdTe absorbers. Here, we focus on solution-deposited stoichiometric CBTSSe films with band gap of 1.59 eV (x ≈ 3) and explore the fundamental film properties. Temperature- and excitation-dependent photoluminescence studies reveal a dominant defect emission at ~1.5 eV and a second deep defect feature at 1.15 eV. From time-resolved terahertz measurements, we find a charge carrier (electron and hole sum) mobility of ~140 cm 2 /Vs—i.e., comparable to values in CIGSSe or Cu 2 ZnSnS 4-x Se x (CZTSSe)—as well as a two-component minority carrier lifetime. A longer-lived lifetime component (~2 ns) arises from bulk recombination. However, strong recombination at the (bare) surface leads to a ~50 ps lifetime, inferior to state-of-the-art CIGSSe or CZTSSe absorbers. This recombination issue may worsen for CBTSSe/CdS interfaces, due to a cliff-like band alignment with 0.6 eV band offset, as revealed by ultraviolet photoemission spectroscopy. A low number of charge carriers within the absorber further contributes to a high series resistance. Employing these films, we also report the highest performance achieved from solution-processed trigonal CBTSSe thin-film photovoltaic devices, with open circuit voltage, short-circuit current density, fill factor and efficiency of 470 mV, 14.3 mA/cm 2 , 43.6% and 2.9%, respectively. The physical measurements provided on the stoichiometric solution-processed CBTSSe absorber further point to critical areas for future improvement of CBTSSe and related photovoltaic cells in the quest for higher efficiency devices based on earth abundant metals.

14 SOLAR ENERGY↗