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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Decoding the Broadband Emission of 2D Pb-Sn Halide Perovskites through High-Throughput Exploration

Unlike single-component 2D metal halide perovskites (MHPs) exhibiting sharp excitonic photoluminescence (PL), a broadband PL emerges in mixed Pb-Sn 2D lattices. Two physical models –self-trapped exciton and defect-induced Stokes-shift – are proposed to explain this unconventional phenomenon. However, the explanations provide limited rationalizations without consideration of the formidable compositional space, and thus, the fundamental origin of broadband PL remains elusive. Herein, the high-throughput automated experimental workflow is established to systematically explore the broadband PL in mixed Pb-Sn 2D MHPs, employing PEA (Phenethylammonium) as a model cation known to work as a rigid organic spacer. Spectrally, the broadband PL becomes further broadened with rapid PEA 2 PbI 4 phase segregation with increasing Pb concentrations during early-stage crystallization. Counterintuitively, MHPs with high Pb concentrations exhibit prolonged PL lifetimes. Hyperspectral microscopy identifies substantial PEA 2 PbI 4 phase segregation in those films, hypothesizing that the establishment of charge transfer excitons by the phase segregation upon crystallization at high-Pb compositions results in distinctive PL properties. In conclusion, these results indicate that two independent mechanisms—defect-induced Stoke-shifts and the establishment of charge transfer excitons by phase segregation—coexist which significantly correlates with the Pb:Sn ratio, thereby simultaneously contributing to the broadband PL emission in 2D mixed Pb-Sn HPs.

2D Pb-Sn halide perovskites↗
DOE OSTI2022

Bifacial all-perovskite tandem solar cells

The efficiency of all-perovskite tandem devices falls far below theoretical efficiency limits, mainly because a widening bandgap fails to increase open-circuit voltage. We report on a bifacial all-perovskite tandem structures with an equivalent efficiency of 29.3% under back-to-front irradiance ratio of 30. This increases energy yield and reduces the required bandgap of a wide-bandgap cell. Open-circuit voltage deficit is therefore minimized, although its performance under only front irradiance is not ideal. The bifacial device needs a sputtered rear transparent electrode, which could reduce photon path length and deteriorate stability of Pb-Sn perovskites. Embedding a light-scattering micrometer-sized particle layer into perovskite to trap light, effectively increases absorptance by 5 to 15% in the infrared region. Using a nonacidic hole transport layer markedly stabilizes the hole-extraction interface by avoiding proton-accelerated formation of iodine. These two strategies together increase efficiency of semitransparent Pb-Sn cells from 15.6 to 19.4%, enabling fabrication of efficient bifacial all-perovskite tandem devices.

14 SOLAR ENERGY↗
DOE OSTI2022

UO 2 -liquid metal suspension fuel concept for enhanced passive safety of LWRs: A heat pipe case study

This work proposes a novel fuel concept for use in light-water type reactors (LWRs): UO 2 particles suspended in a low-melting-point liquid metal (LM). This new fuel form offers lower energy density and higher thermal conductivity, thus enhancing the fuel’s thermal performance compared to sintered UO 2 pellets. Two candidate alloys for the LM are proposed based on previous studies into accident-tolerant fuels: Bi-Pb-Sn and Pb-Sn. Ten research questions are provided to guide future development of this fuel. A simple heat pipe model was constructed by coupling a reactor physics code to a heat transport code and other physics modules. Scoping calculations were performed on this model core as a preliminary investigation into five of the research questions. A fuel with 13 wt% UO 2 was shown to maintain a steady-state peak coolant channel wall temperature below 400 °C, and maintain criticality via self-regulating reactivity feedback. Shortcomings of the present model are discussed in this work, along with proposed future model improvements and fuel development. The appendix provides an example of a reactor concept that could be developed to utilize this fuel, but more modeling and experimental work are needed before a full reactor concept can be developed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Impact of Halogen Groups on the Properties of PEA–Based 2D Pb–Sn Halide Perovskites

Tuning broad emission in 2D Pb–Sn halide perovskites (HPs) is essential for advancing optoelectronic applications, particularly for color-tunable and white-light-emitting devices. This broad emission is linked to structural factors, such as defects and phase segregation of the Pb component within the Pb–Sn system, which are strongly influenced by the molecular structure and chemical properties of spacer cations. Atomic tuning of the spacers via halogenation opens up a new way to fine-tune the molecular properties, enabling further augmentations of HP functionalities. Nevertheless, the distinct broad emission's sensitivity to spacer chemistry remains underexplored. Here, halogenation's influence is systematically investigated on 2D HP emission characteristics using a high-throughput workflow. These findings reveal that the F-containing phenethylammonium (4F-PEA) spacer narrows the broadband PL, whereas Cl broadens it. Through a correlative study, it is found that 4F-PEA reduces not only the local phase segregation but also the defect levels and microstrains in 2D HPs. This is likely attributed to the manifestation of less lattice distortion via stronger surface coordination of the dipole-augmented 4F-PEA. Furthermore, these results highlight halogenation as a key factor in modulating phase segregation and defect density in 2D Pb–Sn HPs, offering a promising pathway to tune the emission for enhanced optoelectronic performance.

2D Pb-Sn halide perovskites↗
DOE OSTI2020

Materials Data on SnPb by Materials Project

SnPb crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Pb is bonded to six equivalent Pb and six equivalent Sn atoms to form PbSn6Pb6 cuboctahedra that share corners with twelve equivalent SnPb6 cuboctahedra, corners with eighteen equivalent PbSn6Pb6 cuboctahedra, edges with six equivalent PbSn6Pb6 cuboctahedra, edges with twelve equivalent SnPb6 cuboctahedra, and faces with eight equivalent PbSn6Pb6 cuboctahedra. All Pb–Pb bond lengths are 3.48 Å. All Pb–Sn bond lengths are 3.49 Å. Sn is bonded to six equivalent Pb atoms to form distorted SnPb6 cuboctahedra that share corners with twelve equivalent PbSn6Pb6 cuboctahedra, corners with twelve equivalent SnPb6 cuboctahedra, edges with six equivalent SnPb6 cuboctahedra, edges with twelve equivalent PbSn6Pb6 cuboctahedra, and faces with two equivalent SnPb6 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnPb3 by Materials Project

Pb3Sn is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Pb is bonded to eight equivalent Pb and four equivalent Sn atoms to form distorted PbSn4Pb8 cuboctahedra that share corners with four equivalent SnPb12 cuboctahedra, corners with fourteen equivalent PbSn4Pb8 cuboctahedra, edges with six equivalent SnPb12 cuboctahedra, edges with twelve equivalent PbSn4Pb8 cuboctahedra, faces with four equivalent SnPb12 cuboctahedra, and faces with sixteen equivalent PbSn4Pb8 cuboctahedra. There are two shorter (3.44 Å) and six longer (3.55 Å) Pb–Pb bond lengths. There are two shorter (3.50 Å) and two longer (3.51 Å) Pb–Sn bond lengths. Sn is bonded to twelve equivalent Pb atoms to form SnPb12 cuboctahedra that share corners with six equivalent SnPb12 cuboctahedra, corners with twelve equivalent PbSn4Pb8 cuboctahedra, edges with eighteen equivalent PbSn4Pb8 cuboctahedra, faces with eight equivalent SnPb12 cuboctahedra, and faces with twelve equivalent PbSn4Pb8 cuboctahedra.

36 MATERIALS SCIENCE↗