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Sellinger, Alan

Publications and source records attributed to Sellinger, Alan.

15 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Boron-10 Doped Polysiloxanes as Matrix Materials for Application in the Simultaneous Detection and Discrimination of Gamma Rays and Fast and Thermal Neutrons

Three boron-10 enriched aromatic molecules have been synthesized and incorporated into two different commercial polysiloxane resins, Shin Etsu KER-6000 and Wacker SilRes H62-C. Scintillating fluorophores, 9,9-dimethyl-2-phenylfluorene (PhF) and 2,5-diphenyloxazole (PPO), were tested in combination with each resin and boron-10 molecule for the simultaneous detection of gamma rays, fast neutrons, and thermal neutrons. Here, the H62-C resin was able to solubilize a large amount of PhF, in excess of 20 wt%. Cure kinetics were controlled through the addition of divinylbenzene and phenyl tris(dimethylsiloxy)silane cross-linker solution to the H62-C resin, with rheology experiments demonstrating a large reduction in time to gelation when 20 wt% cross-linker solution was added, from more than 4 hours to less than 1 hour. These polysiloxane resins can be cured in 3 hours under air, while common poly(vinyltoluene) scintillators require at least 4 days of heating and oxygen-free conditions. PhF-doped KER-6000 with tolyl boronate pinacol ester exhibited the best overall performance with a light yield of 62% relative to EJ-200 and thermal neutron capture at energies up to 103 keVee (84 keVee for EJ254B-5). Additionally, four samples exhibited light yields surpassing an industry-standard boron-doped plastic scintillator, Eljen’s EJ254B-5. Over the course of ten months, the KER-6000 samples showed precipitation of dopant molecules, which reduced their light yield by 15% on average, while H62-C proved to be more stable with only a 6% reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Diversifying hierarchical ionic assembly by docking cations to anions as salt bridges

Here, we expand the diversity of building blocks available for ionic assembly by introducing tertiary (3°) ammonium cations into anion complexes. We use proton transfer between 3° amines and organo-phosphoric acids to generate H-bonding cations (R 3 NH + ) and anions (RHPO 4 – ) that co-assemble with cyanostar macrocycles into assemblies with 2:2:2 stoichiometry. At the heart is a supramolecular dimer where phosphate anions form salt bridges by H-bonding with cations. Unlike conventional 4° ammonium cations, 3,000 commercial amines provide diversity for high-throughput screening of 72 combinations (9 nitrogen bases and 8 acids), producing 13 privileged partners for quantitative assembly. Yields depend on the solvent and sterics of salt bridge formation. Ten more nitrogen bases connect to fluorophores (pyrene), photocatalysts (quinoline), drugs (Cipralex, Zytiga), and ionic liquids (imidazole). The synthesis and examination of 82 new salts exemplify how acid-base chemistry can open a pipeline to a diversity of building blocks for exploring hierarchical ionic assembly.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Strong-Bonding Hole-Transport Layers Reduce Ultraviolet Degradation of Perovskite Solar Cells

The light-emitting diodes (LEDs) used in indoor testing of perovskite solar cells do not expose them to the levels of ultraviolet (UV) radiation that they would receive in actual outdoor use. We report degradation mechanisms of p-i-n-structured perovskite solar cells under unfiltered sunlight and with LEDs. Weak chemical bonding between perovskites and polymer hole-transporting materials (HTMs) and transparent conducting oxides (TCOs) dominate the accelerated A-site cation migration, rather than direct degradation of HTMs. An aromatic phosphonic acid, [2-(9-ethyl-9H-carbazol-3-yl)ethyl]phosphonic acid (EtCz3EPA), enhanced bonding at the perovskite/HTM/TCO region with a phosphonic acid group bonded to TCOs and a nitrogen group interacting with lead in perovskites. A hybrid HTM of EtCz3EPA with strong hole-extraction polymers retained high efficiency and improved the UV stability of perovskite devices, and a champion perovskite minimodule-independently measured by the Perovskite PV Accelerator for Commercializing Technologies (PACT) center-retained operational efficiency of >16% after 29 weeks of outdoor testing.

14 SOLAR ENERGY↗
DOE OSTI2023

Controlling Extraction of Rare Earth Elements Using Functionalized Aryl-vinyl Phosphonic Acid Esters

Ligands that can discriminate between individual rare earth elements are important for production of these critical elements. A set of aryl-vinyl phosphonic acid ligands for extracting rare earth elements were designed and synthesized under the hypothesis that the strength of the rare earth-ligand interactions could be tuned by changing the dipole moment of the ligand. The ligands were synthesized via a two-step reaction procedure using a Heck coupling reaction to functionalize vinyl phosphonic acid, followed by Steglich esterification to obtain high-purity styryl phosphonic acid monoesters with varying dipole moments along the P-C bond. The metal binding strength and composition of the rare earth complexes formed with these styryl phosphonic acid monoesters were experimentally studied by liquid-liquid extraction techniques, while DFT calculations were performed to determine the dipole moments of the free and complexed ligands and the electronic structure of the complexes formed. All three prepared ligands were much stronger extracting agents for europium(III) than the dialkylphosphonic acids usually used for this separation. However, the order of increasing extraction strength was found to match the order of the decreasing calculated dipole moment along the P-C bond of the three styryl-based ligands, rather than correlating with increasing ligand basicity, as reflected by the pK a of the ligands. Finally, these findings suggest that this approach can be used to systematically alter the extraction strength of aromatic phosphonic monoesters for rare earth element purification.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Impact of temperature on light yield and pulse shape discrimination of polysiloxane-based organic scintillators formulated with commercial resins

This work investigates how increased temperature affects neutron/ discrimination and light yield (LY) in several different polysiloxane-based scintillators doped with either 9,9-dimethyl-2-phenylflourene (PhF) or 2,5-diphenyloxazole (PPO) as a primary fluorophore and 9,9-dimethyl-2,7-di((E)-styryl) fluorene (SFS) as the secondary fluorophore. The polysiloxane matrices were prepared from the commercial resins Wacker Lumisil 579 or Shin-Etsu KER-6000. Control scintillators were prepared from poly(vinyltoluene) (PVT), the industry standard matrix, as a reference point for LY and pulse shape discrimination (PSD) measurements. Samples with PhF and PPO dopant concentrations of 1 wt% and 5 wt% in the polysiloxanes and 3 wt% and 5 wt% in the PVT samples were tested at 20 °C, 35 °C, and 50 °C. In the polysiloxane samples, the KER-6000 resin outperformed the Wacker 579 and PhF proved to be a better dopant than PPO in both LY and PSD capabilities. Polysiloxane scintillators showed slight decreases in LY and increases in neutron/discrimination at increased temperatures, while PVT scintillators showed a similar LY decrease with little to no improvement in neutron/discrimination at increased temperatures. Altogether, polysiloxane scintillators may not require recalibration in applications where temperatures increase up to 50 °C.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Influence of fluorescent dopants on the vat photopolymerization of acrylate-based plastic scintillators for application in neutron/gamma pulse shape discrimination

Plastic scintillators, a class of solid-state materials used for radiation detection, were additively manufactured with vat photopolymerization. The photopolymer resins consisted of a primary dopant and a secondary dopant dissolved in a bisphenol A ethoxylate diacrylate-based matrix. The absorptive dopants significantly influence important print parameters, for example, secondary dopants decrease the light penetration depth by a factor > 12×. The primary dopant 2,5-diphenyloxazole had minimal impact on the printing process even when loaded at 25 % by mass of the resin. Working curve measurements, which relate energy dose to cure depth, were performed as a function of feature size to further assess the influence of dopants. Photopatterns smaller than 150 µm width had apparent increases in critical energy dose compared to larger photopatterns, while all resins maintained printed features in line gratings with 50 µm of separation. Printed scintillator monoliths were compared to scintillators cast by traditional molding, demonstrating that the layer-by-layer printing process does not decrease scintillation response. In conclusion, a maximum light output of 31 % of a benchmark plastic scintillator (EJ-200) and successful pulse shape discrimination were achieved with 20 % by mass 2,5-diphenyloxazole as the primary dopant and 0.1 % by mass 9,9-dimethyl-2,7-distyrylfluorene as the secondary dopant in printed scintillator samples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Thermal Properties of Polymer Hole-Transport Layers Influence the Efficiency Roll-off and Stability of Perovskite Light-Emitting Diodes

While the performance of metal halide perovskite light-emitting diodes (PeLEDs) has rapidly improved in recent years, their stability remains a bottleneck to commercial realization. Here, we show that the thermal stability of polymer hole-transport layers (HTLs) used in PeLEDs represents an important factor influencing the external quantum efficiency (EQE) roll-off and device lifetime. We demonstrate a reduced EQE roll-off, a higher breakdown current density of approximately 6 A cm -2 , a maximum radiance of 760 W sr -1 m -2 , and a longer device lifetime for PeLEDs using polymer HTLs with high glass-transition temperatures. Furthermore, for devices driven by nanosecond electrical pulses, a record high radiance of 1.23 MW sr -1 m -2 and an EQE of approximately 1.92% at 14.6 kA cm -2 are achieved. Thermally stable polymer HTLs enable stable operation of PeLEDs that can sustain more than 11.7 million electrical pulses at 1 kA cm -2 before device failure.

14 SOLAR ENERGY↗
DOE OSTI2023

Origins of Photoluminescence Instabilities at Halide Perovskite/Organic Hole Transport Layer Interfaces

Metal halide perovskites are promising for optoelectronic device applications; however, their poor stability under solar illumination remains a primary concern. While the intrinsic photostability of isolated neat perovskite samples has been widely discussed, it is important to explore how charge transport layers—employed in most devices—impact photostability. Here, in this paper, we study the effect of organic hole transport layers (HTLs) on light-induced halide segregation and photoluminescence (PL) quenching at perovskite/organic HTL interfaces. By employing a series of organic HTLs, we demonstrate that the HTL’s highest occupied molecular orbital energy dictates behavior; furthermore, we reveal the key role of halogen loss from the perovskite and subsequent permeation into organic HTLs, where it acts as a PL quencher at the interface and introduces additional mass transport pathways to facilitate halide phase separation. In doing so, we both reveal the microscopic mechanism of non-radiative recombination at perovskite/organic HTL interfaces and detail the chemical rationale for closely matching the perovskite/organic HTL energetics to maximize solar cell efficiency and stability.

14 SOLAR ENERGY↗
DOE OSTI2022

Carbazole-Based Hole Transport Polymer for Methylammonium-Free Tin-Lead Perovskite Solar Cells with Enhanced Efficiency and Stability

As the most commonly used hole transport material (HTM) in tin-lead (Sn-Pb) perovskite solar cells (PSCs), poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) limits the power conversion efficiency (PCE) and stability of the PSCs due to its acidic characteristics. Herein, an easily synthesized polymer HTM poly[(phenyl)imino[9-(2-ethylhexyl)carbazole]-2,7-diyl] (CzAn) with a shallow highest occupied molecular orbital (HOMO) level of -4.95 eV is used in a p-i-n structure, methylammonium-free, Sn-Pb PSC to replace PEDOT:PSS. Upon optimization using doping and surface engineering, high quality Sn-Pb PSCs could be successfully fabricated, boosting the PCE to 22.6% (stabilized PCE of 21.3%) compared with 21.2% for PEDOT:PSS. The perovskite films prepared on the modified CzAn HTM possess improved crystallinity, reduced trap-state density, and larger carrier mobility resulting in PSCs with greatly improved stability.

carrier mobility↗
DOE OSTI2022

Polymer Hole Transport Material Functional Group Tuning for Improved Perovskite Solar Cell Performance

As lead halide perovskites (LHPs) continue to achieve success as a light-harvesting material in perovskite solar cells (PSCs), exploring and understanding other materials in the device stack become increasingly important. Particularly, selection of suitable hole transport materials (HTMs) that demonstrate high performance and stability is imperative in the design of P-I-N PSCs. Presented here are a family of 12 structurally related polymers based on either fluorene or carbazole main chains with select aromatic side groups that introduce tunable properties for use in PSCs. How properties such as the highest occupied molecular orbital energy level, conductivity, glass-transition temperature, and wettability of the HTM affect the PSC performance is explored. Devices that incorporate the polymer HTMs perform well relative to PTAA in benchmark P-I-N PSC architectures while exhibiting similar or superior stability under accelerated aging studies. The relative synthetic simplicity and resultant performance of the HTMs in PSCs coupled with the ability to customize properties with different functional groups demonstrates the potential of this family of HTMs for a variety of LHP materials.

14 SOLAR ENERGY↗
DOE OSTI2022

Plastic Scintillators via Rapid Photoinitiated Cationic Polymerization of Vinyltoluene

Cationic photopolymerization is applied for the rapid curing of a vinyltoluene and fluorophore solution into an efficient plastic scintillator. A hard solid is obtained via UV light-initiated polymerization of vinyltoluene, diaryliodonium salt, 9,9-dimethyl-2-phenylfluorene (PhF), and 9,9-dimethyl-2,7-distyrlfluorene (SFS) at ambient conditions with high conversion rates under a range of cationic photoinitiator concentrations, fluorophore concentrations, and light intensities. Insight into photopolymerization kinetics via photo differential scanning calorimetry (photoDSC) revealed photocuring time scales similar to those achieved in a commercial 3D printing resin. Furthermore, scintillator samples prepared cationically performed well compared to samples of equivalent compositions prepared by a lengthy thermally initiated radical polymerization.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Polymer Hole Transport Materials for Perovskite Solar Cells via Buchwald–Hartwig Amination

The development of low-cost materials for charge-selective contacts that provide good energetic alignment with perovskite active layers, favorable thermal properties, and lead to efficient photoconversion is becoming an increasingly important aspect of the perovskite solar cell (PSC) field. Presented here is a series of polymers based on a one-pot polymerization of aryl dihalides with primary aryl amines to produce solution-processable polymers in high yield, with simple purification, and promising properties for high performing P-I-N PSC devices. How these properties can be tuned by careful selection of the reactant chemical moieties is discussed. Through this strategy, a wide range of relevant properties such as glass transition temperature, highest occupied molecular orbital tuning, and polydispersity are explored. When implemented into devices using a triple-cation FAMACs perovskite active layer, the hole transport material series shows average power conversion efficiencies (PCE) in excess of 17%, which is comparable to controls using state-of-the-art poly(triarylamine). How different synthetic parameters such as the reaction time and purification protocol impact device performance is also investigated.

14 SOLAR ENERGY↗