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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on SmAs by Materials Project

AsSm is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Sm3+ is bonded to six equivalent As3- atoms to form a mixture of corner and edge-sharing SmAs6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Sm–As bond lengths are 2.98 Å. As3- is bonded to six equivalent Sm3+ atoms to form a mixture of corner and edge-sharing AsSm6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SmAs by Materials Project

AsSm is Tetraauricupride structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Sm3+ is bonded in a body-centered cubic geometry to eight equivalent As3- atoms. All Sm–As bond lengths are 3.16 Å. As3- is bonded in a body-centered cubic geometry to eight equivalent Sm3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of the chlorine substitution position of the end-group on intermolecular interactions and photovoltaic performance of small molecule acceptors

The structure–property relationships of small molecular acceptors (SMAs) are a key issue in the molecular design of new-generation acceptor materials for further improving the device efficiencies of polymer solar cells (PSCs). Herein, three couples of SMA isomers were synthesized, based on three central fused ring units and two 1,1-dicyanomethylene-3-indanone (IC) isomer electron-withdrawing terminal units with chlorine substitutions in different positions of its benzene ring: Cl-1 with chlorine on the same side as a C=O group of IC and Cl-2 with chlorine on the same side as the CN groups of IC. Through systematical investigation, we found that the chlorine substitution position of the terminal groups has a regular and significant influence on the molecular packing and photovoltaic performance of the SMAs. The molecular packing behavior of the SMAs is closely related to and determined by the configuration of their terminal groups, no matter which central fused ring of the SMAs is used. In particular, the Cl-1-based SMAs possess a stronger crystallinity with long range ordering packing in their molecular plane direction, while the more abundant and stereoscopic π–π intermolecular interaction in the Cl-2-based SMAs promotes the molecules to form three-dimensional charge transporting channels and leads to their red-shifted absorption and higher electron mobilities. Therefore, the Cl-2-based PSCs exhibit a higher power conversion efficiency (PCE) compared to that of the Cl-1-based devices, and the best PCE of a Cl-2 SMA-based PSC reached 16.42%. These results highlight the importance of the investigation of intermolecular interactions, packing and the arrangement of the SMAs in the solid-state, which may provide direct insights for exploring the relationship between the molecular structure and property of the photovoltaic materials. Moreover, we envision that if fragments such as end groups or side chains with more diverse molecular interactions are added into the design and the subsequent synthesis of the SMAs, this may be beneficial to promoting molecular π–π accumulation and further improving the molecular order, forming suitable molecular packing and morphology in the resulting blend films, and finally affecting the efficiency of the PSCs.

14 SOLAR ENERGY↗
DOE OSTI2022

Effect of the Selective Halogenation of Small Molecule Acceptors on the Blend Morphology and Voltage Loss of High-Performance Solar Cells

Herein, the impacts of the selective halogenation at two different positions of dicyanomethylene-3-indanone (IC) end groups and inner side chains of small molecular acceptors (SMAs) on the P D :SMA interfacial interactions, blend morphology, and resulting photovoltaic properties are described. In this study, four different SMAs (A1, A2, A3, and A4) with the same molecular backbone, but with different degrees of halogenation, are synthesized. The IC end groups on the backbones of the A1 and A3, and A2 and A4 SMAs are chlorinated and fluorinated, respectively; in addition, 6-phenoxyhexyl inner side chains of the A3 and A4 are chlorinated. The SMAs are paired with a chlorinated PBDT-Cl PD to construct organic solar cells (OSCs). The PBDT-Cl:A4-based OSC exhibits the highest power conversion efficiency of 17.2%, outperforming the PBDT-Cl:A1-(13.3%), PBDT-Cl:A2-(15.6%), and PBDT-Cl:A3-based OSC (16.5%). The Cl atoms on the side chains in the A3 and A4 SMAs enhance the molecular/energetic interactions at the P D :SMA interfaces and improve the blend morphology in terms of domain purity and spacing. These effects lead to the improved fill factors and reduced voltage loss of the PBDT-Cl:A3- and PBDT-Cl:A4-based OSCs. This study demonstrates the importance of appropriate halogenation of SMAs in optimizing the blend morphology, reducing voltage loss, and improving OSC performance.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Halogenated Dibenzo[ f , h ]quinoxaline Units Constructed 2D‐Conjugated Guest Acceptors for 19% Efficiency Organic Solar Cells

Abstract Halogenation of Y‐series small‐molecule acceptors (Y‐SMAs) is identified as an effective strategy to optimize photoelectric properties for achieving improved power‐conversion‐efficiencies (PCEs) in binary organic solar cells (OSCs). However, the effect of different halogenation in the 2D‐structured large π‐fused core of guest Y‐SMAs on ternary OSCs has not yet been systematically studied. Herein, four 2D‐conjugated Y‐SMAs (X‐QTP‐4F, including halogen‐free H‐QTP‐4F, chlorinated Cl‐QTP‐4F, brominated Br‐QTP‐4F, and iodinated I‐QTP‐4F) by attaching different halogens into 2D‐conjugation extended dibenzo[ f , h ]quinoxaline core are developed. Among these X‐QTP‐4F, Cl‐QTP‐4F has a higher absorption coefficient, optimized molecular crystallinity and packing, suitable cascade energy levels, and complementary absorption with PM6:L8‐BO host. Moreover, among ternary PM6:L8‐BO:X‐QTP‐4F blends, PM6:L8‐BO:Cl‐QTP‐4F obtains a more uniform and size‐suitable fibrillary network morphology, improved molecular crystallinity and packing, as well as optimized vertical phase distribution, thus boosting charge generation, transport, extraction, and suppressing energy loss of OSCs. Consequently, the PM6:L8‐BO:Cl‐QTP‐4F‐based OSCs achieve a 19.0% efficiency, which is among the state‐of‐the‐art OSCs based on 2D‐conjugated Y‐SMAs and superior to these devices based on PM6:L8‐BO host (17.70%) and with guests of H‐QTP‐4F (18.23%), Br‐QTP‐4F (18.39%), and I‐QTP‐4F (17.62%). The work indicates that halogenation in 2D‐structured dibenzo[ f , h ]quinoxaline core of Y‐SMAs guests is a promising strategy to gain efficient ternary OSCs.

14 SOLAR ENERGY↗
DOE OSTI2022

Tethered Small-Molecule Acceptors Simultaneously Enhance the Efficiency and Stability of Polymer Solar Cells

For polymer solar cells (PSCs), the mixture of polymer donors and small-molecule acceptors (SMAs) is fine-tuned to realize a favorable kinetically trapped morphology and thus a commercially viable device efficiency. However, the thermodynamic relaxation of the mixed domains within the blend raises concerns related to the long-term operational stability of the devices, especially in the record-holding Y-series SMAs. Here, a new class of dimeric Y6-based SMAs tethered with differential flexible spacers is reported to regulate their aggregation and relaxation behavior. In their polymer blends with PM6, it is found that they favor an improved structural order relative to that of Y6 counterpart. Most importantly, the tethered SMAs show large glass transition temperatures to suppress the thermodynamic relaxation in mixed domains. For the high-performing dimeric blend, an unprecedented open circuit voltage of 0.87 V is realized with a conversion efficiency of 17.85%, while those of regular Y6-base devices only reach 0.84 V and 16.93%, respectively. Most importantly, the dimer-based device possesses substantially reduced burn-in efficiency loss, retaining more than 80% of the initial efficiency after operating at the maximum power point under continuous illumination for 700 h. In conclusion, the tethering approach provides a new direction to develop PSCs with high efficiency and excellent operating stability.

14 SOLAR ENERGY↗
DOE OSTI2024

Impact of Linker Engineering in Core‐Linked Dimeric Acceptors for High‐Performance Organic Solar Cells

Abstract The dimerization of small molecule acceptors (SMAs) is a promising strategy for enhancing the long‐term stability and power conversion efficiency (PCE) of organic solar cells (OSCs). However, the reported DSMAs are primarily limited to end‐linked molecular configurations, highlighting the need for further exploration of various dimer architectures. Herein, the development of two distinct core‐linked dimerized SMAs (DYF‐V and DYF‐E) are reported with tailored linker structures (vinylene and ethynyl, respectively), achieving high‐performance OSCs (PCE = 18.53%). Interestingly, a subtle change in the linker structures results in markedly different molecular properties and photovoltaic performances of the dimer acceptors. DYF‐E with an ethynyl linker exhibits more twisted backbone conformation and mitigated aggregation property compared to DYF‐V, inducing desirable blend morphologies with a polymer donor including high crystallinity, face‐on oriented packing structures, and well‐intermixed domains. Thus, the DYF‐E‐based OSCs exhibit a high PCE (17.02%), which significantly outperforms the DYF‐V‐based OSCs (PCE = 9.98%). Furthermore, the ternary OSCs based on DYF‐E achieve a higher PCE of 18.53%. Thus, this study highlights the significance of selecting an appropriate linker in core‐linked dimerized SMAs for producing high‐performance OSCs.

Oh, Shinbee↗
DOE OSTI2023

Introducing a Phenyl End Group in the Inner Side Chains of A‐DA'D‐A Acceptors Enables High‐Efficiency Organic Solar Cells Processed with Nonhalogenated Solvent

Abstract Power conversion efficiency (PCE) of organic solar cells (OSCs) processed by nonhalogenated solvents is unsatisfactory due to the unfavorable morphology. Herein, two new small molecule acceptors (SMAs) Y6‐Ph and L8‐Ph are synthesized by introducing a phenyl end group in the inner side chains of the SMAs of Y6 and L8‐BO, respectively, for overcoming the excessive aggregation of SMAs in the long‐time film forming processed by nonhalogenated solvents. First, the effect of the film forming time on the aggregation property and photovoltaic performance of Y6, L8‐BO, Y6‐Ph, and L8‐Ph is studied by using the commonly used solvents: chloroform (CF) (rapid film forming process) and chlorobenzene (CB) (slow film forming process). It is found that Y6‐ and L8‐BO‐based OSCs exhibit a dramatic drop in PCE from CF‐ to CB‐processed devices owing to the large phase separation, while the Y6‐Ph and L8‐Ph based OSCs show obviously increased PCEs Furthermore, L8‐Ph‐based OSCs processed by nonhalogenated solvento‐xylene (o‐XY) achieved a high PCE of 18.40% with an FF of 80.11%. The results indicate that introducing a phenyl end group in the inner side chains is an effective strategy to modulate the morphology and improve the photovoltaic performance of the OSCs processed by nonhalogenated solvents.

Chemistry↗
DOE OSTI2022

High-Performance Non-fullerene organic solar cells enabled by noncovalent Conformational locks and Side-Chain engineering

Three novel small molecular acceptors (SMAs) BO-2F, BO-C8-2F and BO-C2C6-C8-2F were designed and synthesized. These acceptors all possess planar molecular backbone because of the introduction of intramolecular noncovalent interaction. Among them, BO-C2C6-C8-2F with four side chains, which has the highest solubility, can form more appropriate nanomorphology when blending with PBDB-T. Hence, organic solar cells (OSCs) based on PBDB-T:BO-C2C6-C8-2F displayed an outstanding power convesion efficiency (PCE) of 14.25%, which is higher than BO-2F and BO-C8-2F based ones. To the best of our knowledge, the PCE of 14.25% is one of the highest for the OSCs based on A-π-D-π-A type SMAs. Finally, our results have demonstrated that the combination of side-chain engineering and intramolecular conformation lock has a great prospect in the design of high performance SMAs for OSCs.

14 SOLAR ENERGY↗
DOE OSTI2021

Enhanced superelasticity of nanocrystalline NiTi/NiTiNbFe laminar composite

This study explores a new concept of the synergy between two constituent shape memory alloys (SMAs) in a composite to achieve a wide superelastic temperature window. In this work, a nanocrystalline NiTi/NiTiNbFe dual-SMA composite is designed, in which two constituent SMAs are both capable of stress-induced martensitic transformation, but within different temperature ranges. Based on the principle of lattice strain matching between the two SMAs, superelastic martensitic transformation in one induces superelastic transformation in the other at temperatures the latter will not when standing alone. Furthermore, via this synergy the composite is able to achieve an ultra-wide superelastic temperature window of 336°C, from -196 to 140°C, with a ~5% tensile strain recovery and high superelastic stresses in the range of 700~1400 MPa. Such properties appear superior to all NiTi-based shape memory alloys to date.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Shock-induced transformation of nitinol shape memory alloy: Effect of stress state on transformation

Due to its numerous practical applications and intriguing phase transformation behavior, shape memory alloys (SMAs) have garnered significant research and development interests. In the past, most studies on the mechanical behavior of SMAs have been conducted under uniaxial stress loadings. Limited research on SMAs under shock loading has not provided conclusive results regarding their transformation behavior and transformation stress under such loading. Additionally, there is a lack of comprehensive understanding regarding the effects of different stress states on transformation behavior. The main objectives of this study are to address these issues. To achieve these objectives, a series of shock wave experiments were designed and conducted. Additionally, quasi-static and dynamic uniaxial stress experiments were carried out to establish a baseline for comparison. The results revealed that the transformation stress under dynamic uniaxial strain shock loading was approximately 1.92 GPa in contrast to 0.5 GPa (quasi-static) to 0.8 GPa (dynamic) observed in uniaxial stress loading. The transformation behavior exhibited noticeable rate sensitivity for both types of loading. There appeared to be a critical strain rate above which the austenite phase was driven to a metastable state. This estimated critical axial strain rate along the loading direction was approximately 2 × 10 3 /s–4 × 10 3 /s for uniaxial stress loading and approximately 2 × 10 6 /s for uniaxial strain loading. The apparent high transformation stress for uniaxial strain loading can likely be attributed to a combination of high-pressure confinement and high strain rate. Furthermore, determining their relative contributions remains an open issue.

36 MATERIALS SCIENCE↗
DOE OSTI2023

19.32% Efficiency Polymer Solar Cells Enabled by Fine-Tuning Stacking Modes of Y-Type Molecule Acceptors: Synergistic Bromine and Fluorine Substitution of the End Groups

Here, the success of Y6-type nonfullerene small molecule acceptors (NF-SMAs) in polymer solar cells (PSCs) can be attributed to their unique honeycomb stacking style, which leads to favorable thin-film morphologies. The intermolecular interactions related to the crystallization tendency of these NF-SMAs is closely governed by their electron accepting end groups. For example, the high performance Y6 derivative L8-BO (BTP-4F) presents three types of stacking modes in contrast to two stacking modes of Y6. Hence, it is ultimately interesting to obtain more insight on the packing properties and the preferences influenced by chemical modifications such as end group engineering. This work designs and synthesizes asymmetric and symmetric L8-BO derivatives with brominated end groups and explores the stacking preferences in various modes. The asymmetric BTP-3FBr displays an optimized crystallization tendency and thin film morphology, leading to a decent power conversion efficiency (PCE) of 18.34% in binary devices and a top PCE of 19.32% in ternary devices containing 15 wt% IDIC as the second acceptor.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Layer-by-Layer Organic Solar Cells Enabled by 1,3,4-Selenadiazole-Containing Crystalline Small Molecule with Double-Fibril Network Morphology

A double-fibril network of the photoactive layer morphology is recognized as an ideal structure facilitating exciton diffusion and charge carrier transport for high-performance organic solar cells (OSCs). However, in the layer-by-layer processed OSCs (LbL-OSCs), polymer donors and small molecule acceptors (SMAs) are separately deposited, and it is challenging to realize a fibril network of pure SMAs with the absence of tight interchain entanglement as polymers. Here, in this work, crystalline small molecule donors (SMDs), named TDZ-3TR and SeDZ-3TR, were designed and introduced into the L8-BO acceptor solution, forcing the phase separation and molecular fibrilization. SeDZ-3TR showed higher crystallinity and lower miscibility with L8-BO acceptor than TDZ-3TR, enabling more driving force to favor the phase separation and better molecular fibrilization of L8-BO. On the other hand, two donor polymers of PM6 and D18 with different fibril widths and lengths were put together to optimize the fibril network of the donor layer. The simultaneously optimization of the acceptor and donor layers resulted in a more ideal double-fibril network of the photoactive layer and an impressive power conversion efficiency (PCE) of 19.38 % in LbL-OSCs.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A Difluoro‐Methoxylated Ending‐Group Asymmetric Small Molecule Acceptor Lead Efficient Binary Organic Photovoltaic Blend

Abstract Developing a new end group for synthesizing asymmetric small molecule acceptors (SMAs) is crucial for achieving high‐performance organic photovoltaics (OPVs). Herein, an asymmetric small molecule acceptor, BTP‐BO‐4FO, featuring a new difluoro‐methoxylated end‐group is reported. Compared to its symmetric counterpart L8‐BO, BTP‐BO‐4FO exhibits an upshifted energy level, larger dipole moment, and more sequential crystallinity. By adopting two representative and widely available solvent additives (1‐chloronaphthalene (CN) and 1,8‐diiodooctane (DIO)), the device based on PM6:BTP‐BO‐4FO (CN) photovoltaic blend demonstrates a power conversion efficiency (PCE) of 18.62% with an excellent open‐circuit voltage (V OC ) of 0.933 V, which surpasses the optimal result of L8‐BO. The PCE of 18.62% realizes the best efficiencies for binary OPVs based on SMAs with asymmetric end groups. A series of investigations reveal that optimized PM6:BTP‐BO‐4FO film demonstrates similar molecular packing motif and fibrillar phase distribution as PM6:L8‐BO (DIO) does, resulting in comparable recombination dynamics, thus, similar fill factor. Besides, it is found PM6:BTP‐BO‐4FO possesses more efficient charge generation, which yields betterV OC –J SC balance. This study provides a new ending group that enables a cutting‐edge efficiency in asymmetric SMA‐based OPVs, enriching the material library and shed light on further design ideas.

Chemistry↗
DOE OSTI2022

Verifying the structure-property-performance relationship of Y6-based small molecule acceptors by alkoxy-side chain isomerization and conjugated skeleton asymmetry

Non-fullerene small molecule acceptors (NF-SMAs) such as Y6 derivatives were the current working horse for the top performing polymer solar cells (PSCs). For this reason, numerous chemical modifications have been explored for establishing structure–property-performance relationship for Y6-based NF-SMAs. In this work, we explored the isomerization on asymmetrical Y6 derivatives by varying the position of alkoxy side chain on the thiophene linkage between the core and one of the end groups of Y6. The isomers with differences in conformational restriction raised by noncovalent interactions as well as steric hindrance revealed distinctive behavior in crystallization and polymorphism, which led to a significant contrast in PSC performances. Here the X-TO1 molecule with alkoxy side chain facing the end group (outward) displayed preferred molecular configuration and polymorph, delivering power conversion efficiency (PCE) of 15.63%, while its isomer X-TO2 showed coexisted polymorphs significantly increased the charge recombination in the PSC devices led to a low PCE around 3%. This structure–property-performance relationship not only highlighted the elegancy of isomerization in tuning the photovoltaic performances but also identified polymorphism as one of the causes for impairing photovoltaic performances of PSCs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Parallel projection—An improved return mapping algorithm for finite element modeling of shape memory alloys

Here, we present a novel finite element analysis of inelastic structures containing Shape Memory Alloys (SMAs). Phenomenological constitutive models for SMAs lead to material nonlinearities, that require substantial computational effort to resolve. Finite element analysis methods, which rely on Gauss quadrature integration schemes, must solve two sets of coupled differential equations: one at the global level and the other at the local, i.e. Gauss point level. In contrast to the conventional return mapping algorithm, which solves these two sets of coupled differential equations separately using a nested Newton procedure, we propose a scheme to solve the local and global differential equations simultaneously. In the process we also derive closed-form expressions used to update the internal/constitutive state variables, and unify the popular closest-point and cutting plane methods with our formulas. Numerical testing indicates that our method allows for larger thermomechanical loading steps and provides increased computational efficiency, over the standard return mapping algorithm.

42 ENGINEERING↗
DOE OSTI2020

On the elastocaloric effect in CuAlBe shape memory alloys: A quantitative phase-field modeling approach

We report the reversible stress-induced phase transformation in shape memory alloys (SMAs) is a dissipative process during which heat is absorbed or released. The inherent temperature variations inside the material has an elastocaloric effect (eCE) with appealing applications in solid-state cooling technology such as compact and efficient on-board refrigeration system for eletronic devices. In this manuscript, we conduct the first study of eCE of CuAlBe SMAs utilizing phase-field modeling. For an applied stress of 500 MPa, the results for polycrystalline Cu-Al11-2Be (at. %) show a minimum adiabatic unloading temperature change of -10 K over a pseudoelastic window of 40 K. In the absence of plastic deformation, the material demonstrates good reproducibility of the eCE over a few loading–unloading cycles. The presence of plastic deformation is found to cause functional fatigue that deteriorates the cooling capacity; however, the coefficient of performance only decreases from 9.04 to 8.03, which is still a very good value. These results place CuAlBe as a frontrunner SMA for solid-state cooling compared to the expensive NiTi.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Combinatorial Synthesis and High-Throughput Characterization of Microstructure and Phase Transformation in Ni–Ti–Cu–V Quaternary Thin-Film Library

Ni–Ti–based shape memory alloys (SMAs) have found widespread use in the last 70 years, but improving their functional stability remains a key quest for more robust and advanced applications. Named for their ability to retain their processed shape as a result of a reversible martensitic transformation, SMAs are highly sensitive to compositional variations. Alloying with ternary and quaternary elements to fine-tune the lattice parameters and the thermal hysteresis of an SMA, therefore, becomes a challenge in materials exploration. Combinatorial materials science allows streamlining of the synthesis process and data management from multiple characterization techniques. In this study, a composition spread of Ni–Ti–Cu–V thin-film library was synthesized by magnetron co-sputtering on a thermally oxidized Si wafer. Composition-dependent phase transformation temperature and microstructure were investigated and determined using high-throughput wavelength dispersive spectroscopy, synchrotron X-ray diffraction, and temperature-dependent resistance measurements. Of the 177 compositions in the materials library, 32 were observed to have shape memory effect, of which five had zero or near-zero thermal hysteresis. These compositions provide flexibility in the operating temperature regimes that they can be used in. A phase map for the quaternary system and correlations of functional properties are discussed with respect to the local microstructure and composition of the thin-film library.

42 ENGINEERING↗