Molecular Orbital Energy Levels Research Articles

In Situ Polymerized Quasi-Solid Electrolytes Compounded with Ionic Liquid Empowering Long-Life Cycling of 4.45 V Lithium-Metal Battery.

High-voltage resistant quasi-solid-state polymer electrolytes (QSPEs) are promising for enhancing the energy density of lithium-metal batteries in practice. However, side reactions occurring at the interfaces between the anodes or cathodes and QSPEs considerably reduce the lifespan of high-voltage LMBs. In this study, a copolymer of vinyl ethylene carbonate (VEC) and poly(ethylene glycol) diacrylate (PEGDA) was used as the framework, with a cellulose membrane (CE) as the supporting layer. Based on density functional theory calculations, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI), an ionic liquid, was screened because of its lowest unoccupied molecular orbital energy level as a modifying agent for the in situ P(VECx-EGy)/Pyrz/LiTFSI@CE QSPEs synthesis. Pyr14+, with a lithiophobic alkyl chain, forms a dense positive ion shielding layer on the protruding tips of deposited lithium, facilitating uniform and smooth lithium deposition. Pyr14TFSI assists in constructing a stable solid electrolyte interphase (SEI) layer on the Li surface enriched with LiF, Li3N, and RCOOLi. The modulation of lithium deposition behavior on the anode by Pyr14TFSI ensures stable Li plating/stripping for >1500 h. A Li-Cu cell exhibits stable cycling for >200 cycles at a current density of 0.05 mA cm-2, with an average Coulombic efficiency of 92.7%. In situ polymerization ensures that P(VECx-EGy)/Pyrz/LiTFSI@CE QSPEs exhibit excellent interface compatibility with the anode and the cathode. The CR2032 button cell Li|P(VEC1-EG0.06)/Pyr0.4/LiTFSI@CE|LiCoO2 demonstrates stable cycling with a negligible capacity decay of 0.083% per cycle for >390 cycles at 25 °C and 0.2 C when using a high-voltage LiCoO2 (4.45 V) cathode. Furthermore, a 7.1 mAh pouch cell achieves stable charge-discharge cycles, confirming the pronounced stability of the as-fabricated QSPE at the interfaces of the high-voltage LiCoO2 cathode and Li anode.

Synthesis and Photophysical Characterizations of Benzimidazole Functionalized BODIPY Dyes.

Herein, a series of new BODIPY dyes substituted by 2-phenyl benzimidazole units at the meso (C8) position including methyl/ethyl, phenyl, or p-methoxyphenyl moieties at the distal and proximal positions of the BODIPY core have been successfully synthesized and their photophysical characteristics were analyzed. Experimentally investigating absorption and fluorescence profiles in the THF media was followed by density functional theory (DFT) calculations to clarify photophysical features. Theoretical analyses have revealed that upon excitation, both electrons and holes are confined solely within the BODIPY core. The energy levels of the frontier molecular orbitals converge depending on the presence of the phenyl and p-methoxyphenyl substituents. The orbital distributions of both electron and hole were in the -3 and -5 positions, which demonstrates a continuous conjugation with the BODIPY core at these sites. However, the electron density present on the phenyl rings located at the -1, -7, and -8 (meso) positions was found to be negligible. The benzimidazole-BODIPYs exhibited photodynamic activity (Φ∆) ranging from ~ 7% to ~ 11%, determined by a comparative method. Moreover, the compounds have shown to maintain their stability thermally in a non-reactive/inert environment up to temperatures surpassing 300°C, exhibiting primarily a two-phase decomposition process. These compounds have the potential to function as antibacterial and anti-biofilm agents when used in concentrations ranging from 0.5 to 2.0mg/mL. The results provide a basis for evaluating heterocyclic benzimidazole units on photophysical processes containing BODIPY chromophores.

IDTI based copolymers for p-type organic field-effect transistors

Organic semiconductors received more and more attention in the past few years. Development some novel chromophore with the strong electron-deficient to construct donor–acceptor polymers plays a crucial role for the development of the organic semiconductors. A new acceptor indaceno[1,2-b:5,6-b′]dithiophene)-2,7-diylbis(methan-1-yl-1-ylidene))bis(6-bromo-indolin-2-one) (IDTI, M1), as well as a IIDT-based polymer P1 were designed in this work, and for the first time applied in the OFET. The results shows that the P1 present not only a strong aggregation, but also a suitable highest occupied molecular orbital (HOMO) energy level. As a consequent, the P1 exhibited a p-type behavior with the hole mobility up to 0.29 cm2 V−1 s−1. This work demonstrated that the IDTI chromophore is a promising electron-deficient block for the constructing donor–acceptor high performance semiconductor polymers.

Critical role of the end-group acceptor in enhancing the efficiency of indacenodithiophene-benzothiadiazole-linked nonfullerene organic solar cells through morphology optimization

Solution-processed organic solar cells (OSCs) have great promise for next-generation solar energy conversion technologies. Innovative acceptors are constantly being designed to improve device efficiency. In this work, we designed and synthesized a series of A–π–D–π–A type non-fullerene acceptor (NFA) molecules, named IB-TOT, IB-TOM, IB-IOO, and IB-IOM for their applications in OSCs. All molecules showed high thermal stability, broad photoabsorption, and relatively lower highest occupied molecular orbital (HOMO) energy levels from −5.48 eV to −5.58 eV. The optimized OSCs based on these NFAs and PTB7-Th donor deliver power conversion efficiencies (PCEs) of 8.19%, 5.50%, 2.42%, and 3.10% for IB-TOT, IB-TOM, IB-IOO, and IB-IOM molecules, respectively. The higher PCE of IB-TOT-based OSCs is attributed to their excellent miscibility and superior interpenetrating network morphology compared to the other three compounds. These results demonstrate that using the 3-ethylrhodanine acceptor unit to construct the NFA molecule is a successful approach for outstanding achievement in OSCs.

Novel alkyne chromophore of the isophorone derivatives: synthesis, electrochemical evaluation, DFT, and processable bottom contact/top-gate OFET applications

Fused alkyne molecules are important in organic semiconductors due to their desirable properties. Here, we report the design and synthesis of a new series of A–π–D molecules (III–VII) that can serve as mild electron acceptors to generate wide-bandgap p-type small compounds for use in organic field-effect transistors. The incorporation of donor units into fused isophorone frameworks can be used to tune the frontier molecular orbital energies. The electrochemical, optical, and thermal properties of the compounds were characterized. Compound VI, which has a fused phenyl-substituted alkyne moiety, had the highest occupied molecular orbital energy level as determined by optical and electrochemical analysis. Density functional theory calculations revealed that compounds VI and III had lower hole reorganization energy (λh) than the corresponding isophorone extended conjugated-based compounds (I–II). Conversely, compounds I and II had lower electron reorganization energy (λe) than the corresponding fused alkyne compounds. This is in line with the observed adiabatic ionization potential and electron affinity values. Consequently, devices fabricated with compound VI exhibited high mobility and low threshold voltage.

Cyclometalated Iridium(III) Complexes Containing Viologen-Modified Phenylpyridine Ligands as Electroluminochromic Active Molecules for Information Display.

Electroluminochromic (ELC) materials have garnered significant research interest because of their potential applications in lighting, displaying, and sensing. These materials exhibit reversible modulation of photoluminescence under low-voltage stimuli. Here five phosphorescent iridium(III) complexes are reported featuring viologen-substituted 2-phenylpyridine (Vppy) ligands acting as electroactive components. Four of the complexes are bis-cyclometalated and coordinated with either neutral bipyridine derivatives or negatively charged 2-picolinate. The remaining complex is heteroleptic tris-cyclometalated, containing one Vppy and two 2-phenylquinoline ligands. Upon photoexcitation, the bis-cyclometalated complexes exhibit orange to red phosphorescence originating from mixed triplet metal-to-ligand charge transfer (3MLCT) and intraligand (3IL) dπ(Ir)/π(Vppy) → π*(Vppy) state, whereas the tris-cyclometalated complex is non-emissive due to a low Ir(IV/III) oxidation potential favoring oxidative quenching by the viologen pendants. When the cationic viologens are electrochemically reduced to their neutral form, the bis-cyclometalated complexes show a remarkable blue-shift in their phosphorescence maxima due to increased energy levels of the Vppy molecular orbitals. In the case of the tris-cyclometalated complex, reduction of the viologen groups interrupts the quenching process, leading to a luminescence turn-on. These complexes are used to develop ELC devices, which exhibit reversible luminescence response in terms of color or on-off switching under a low voltage of 2V.

In Situ Construction of Inorganics-Rich Cathode-Electrolyte Interface toward Long-Life Prussian White Cathode.

Prussian white (PW) is one of the most promising candidates as a cathode for sodium-ion batteries (SIBs) because of its high theoretical capacity, excellent rate performance, and low production cost. However, PW materials suffer severe capacity decay during long-term cycling. In this work, a robust cathode electrolyte interface (CEI) is designed on the PW cathode by employing cresyl diphenyl phosphate (CDP) and adiponitrile (ADN) as electrolyte additives. CDP and ADN possess higher highest occupied molecular orbital energy levels (HOMO) than other solvents, leading to the preferential decomposition of CDP and ADN to construct an inorganics-rich CEI layer in situ on the PW cathode. Benefiting from this CEI layer, the degradation of PW is effectively inhibited during the long cycling. The Na||PW cell achieves an excellent cycling performance with a capacity retention of 85.62% after 1400 cycles. This work presented here provides a feasible strategy for improving the cycling performance of PW by electrolyte modification.

Self-Assembled Molecules with Asymmetric Backbone for Highly Stable Binary Organic Solar Cells with 19.7 % Efficiency.

The hole-transporting material (HTM), poly (3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT : PSS), is the most widely used material in the realization of high-efficiency organic solar cells (OSCs). However, the stability of PEDOT : PSS-based OSCs is quite poor, arising from its strong acidity and hygroscopicity. In addition, PEDOT : PSS has an absorption in the infrared region and high highest occupied molecular orbital (HOMO) energy level, thus limiting the enhancement of short-circuit current density (Jsc) and open-circuit voltage (Voc), respectively. Herein, two asymmetric self-assembled molecules (SAMs), namely BrCz and BrBACz, were designed and synthesized as HTM in binary OSCs based on the well-known system of PM6 : Y6, PM6 : eC9, PM6 : L8-BO, and D18 : eC9. Compared with BrCz, BrBACz shows larger dipole moment, deeper work function and lower surface energy. Moreover, BrBACz not only enhances photon harvesting in the active layer, but also minimizes voltage losses as well as improves interface charge extraction/ transport. Consequently, the PM6 : eC9-based binary OSC using BrBACz as HTM exhibits a champion efficiency of 19.70 % with a remarkable Jsc of 29.20 mA cm-2 and a Voc of 0.856 V, which is a record efficiency for binary OSCs so far. In addition, the unencapsulated device maintains 95.0 % of its original efficiency after 1,000 hours of storage at air ambient, indicating excellent long-term stability.

Self‐Assembled Molecules with Asymmetric Backbone for Highly Stable Binary Organic Solar Cells with 19.7 % Efficiency

AbstractThe hole‐transporting material (HTM), poly (3,4‐ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT : PSS), is the most widely used material in the realization of high‐efficiency organic solar cells (OSCs). However, the stability of PEDOT : PSS‐based OSCs is quite poor, arising from its strong acidity and hygroscopicity. In addition, PEDOT : PSS has an absorption in the infrared region and high highest occupied molecular orbital (HOMO) energy level, thus limiting the enhancement of short‐circuit current density (Jsc) and open‐circuit voltage (Voc), respectively. Herein, two asymmetric self‐assembled molecules (SAMs), namely BrCz and BrBACz, were designed and synthesized as HTM in binary OSCs based on the well‐known system of PM6 : Y6, PM6 : eC9, PM6 : L8‐BO, and D18 : eC9. Compared with BrCz, BrBACz shows larger dipole moment, deeper work function and lower surface energy. Moreover, BrBACz not only enhances photon harvesting in the active layer, but also minimizes voltage losses as well as improves interface charge extraction/ transport. Consequently, the PM6 : eC9‐based binary OSC using BrBACz as HTM exhibits a champion efficiency of 19.70 % with a remarkable Jsc of 29.20 mA cm−2 and a Voc of 0.856 V, which is a record efficiency for binary OSCs so far. In addition, the unencapsulated device maintains 95.0 % of its original efficiency after 1,000 hours of storage at air ambient, indicating excellent long‐term stability.

Photoswitchable optoelectronic properties of 2D MoSe2/diarylethene hybrid structures

The ability to modulate optical and electrical properties of two-dimensional (2D) semiconductors has sparked considerable interest in transition metal dichalcogenides (TMDs). Herein, we introduce a facile strategy for modulating optoelectronic properties of monolayer MoSe2 with external light. Photochromic diarylethene (DAE) molecules formed a 2-nm-thick uniform layer on MoSe2, switching between its closed- and open-form isomers under UV and visible irradiation, respectively. We have discovered that the closed DAE conformation under UV has its lowest unoccupied molecular orbital energy level lower than the conduction band minimum of MoSe2, which facilitates photoinduced charge separation at the hybrid interface and quenches photoluminescence (PL) from monolayer flakes. In contrast, open isomers under visible light prevent photoexcited electron transfer from MoSe2 to DAE, thus retaining PL emission properties. Alternating UV and visible light repeatedly show a dynamic modulation of optoelectronic signatures of MoSe2. Conductive atomic force microscopy and Kelvin probe force microscopy also reveal an increase in conductivity and work function of MoSe2/DAE with photoswitched closed-form DAE. These results may open new opportunities for designing new phototransistors and other 2D optoelectronic devices.

Cost-effective polymer donors based on pyridine for efficient nonfullerene polymer solar cells

Developing cost-effective polymer donors that can match nonfullerene acceptors is very important for practical applications of polymer solar cells (PSCs). In this work, low-cost 3-fluoropyridine and pyridine were employed as acceptor unit cores to construct cost-effective polymers PBDT-FPy, PBDT-Py and PBDF-Py by copolymerizing with commercially available donor units. PBDT-FPy, PBDT-Py and PBDF-Py show wide-bandgap of 2.08, 2.15 and 2.05 eV, respectively. Due to the strong electronegativity of nitrogen atom in pyridine and Nδ− … Hδ+ noncovalent dipole-dipole interactions, all polymers exhibit deep-lying highest-occupied molecular orbital (HOMO) energy levels, strong intermolecular π-π interaction and good planarity. The PBDT-FPy: Y6 based device exhibits a power conversion efficiency (PCE) of 8.34%, while the performance of PBDT-Py: Y6 and PBDF-Py: Y6 devices was significantly improved, with PCE of 10.02% and 10.00%. The results indicate that pyridine with simple structure and low synthetic cost is a promising building block to construct high-performance cost-effective polymer donors for application in PSCs.

Syntheses and Properties of Hole-Transporting Biindenofluorenes.

Described herein is a straightforward approach to synthesizing three biindenofluorene (BIF) derivatives, composed of antiaromatic indenofluorene units, which are the first non-alternant congeners of known bipentacene. Dimerization of indeno[1,2-b]fluorene and indeno[2,1-c]fluorene units by connecting carbons 3 and 3' and carbons 2 and 2', respectively, is shown to influence the highest occupied and lowest unoccupied molecular orbital energy levels of the resulting BIFs, affording band gaps (1.5-1.6 eV) that are smaller than that of a known indenofluorene polymer (2.3 eV). The hole mobilities of BIFs were determined to be ∼10-2 cm2 V-1 s-1.

Effect of nanofillers with different energy levels on the electrical properties of epoxy‐based nanocomposites

AbstractThe authors investigate the effects of nanofillers with varying band‐gap energies on the space charge properties, breakdown field strength, and bulk resistivity of epoxy (EP)‐based composites. Additionally, the molecular orbital distribution of both the epoxy resin and nanofillers were examined through density functional theory. Experimental results indicate that the space charge accumulation within silicon dioxide/EP and germanium oxide/EP is reduced, leading to a more uniformly distributed electric field intensity within the specimen when compared to epoxy. As a result, both materials exhibit improved AC breakdown field strength and volume resistivity. Conversely, the amount of charge accumulated within tin dioxide/EP is higher, resulting in lower breakdown field strength than epoxy. The lowest unoccupied molecular orbital and the highest occupied molecular orbital energy level differences between epoxy and nanofillers introduce electron traps and hole traps at the interface, forming interfacial traps that affect the space charge distribution within the specimen, as well as the trap energy levels within the material. From the experimental results, shallow traps promote space charge accumulation and reduce the breakdown field strength, while deep traps have the opposite effect.

Surface Work Function Modifier to Modulate Electrolyte Decomposition on Negative Electrode in Lithium‐Ion Batteries

AbstractThe persistent decomposition of electrolytes on graphite and silicon electrodes in lithium‐ion batteries (LIBs) is typically mitigated by the formation of a solid electrolyte interphase (SEI). However, the inadequate formation and chemo‐mechanical degradation of SEI leads to re‐exposure of electrode to electrolyte, contributing to the deterioration of LIBs. To address this issue, tris(2,4‐pentanedionato)indium(III) (InAc) is incorporated into the work function tailoring additive. While conventional additives strengthen the chemo‐mechanical properties of SEI through compositional modifications derived from specific elements, InAc uniquely alters charge transfer across the electrode surface, facilitated by high or low work function layer. This additive establishes an interlayer between the SEI and graphite/SiO surfaces, attributed to its tailored lowest unoccupied molecular orbital energy level. Consequently, the exposure of graphite surface to the electrolyte is minimized by interlayer during cycling. The interlayer possesses a higher work function than lithiated graphite and suppresses further electrolyte decomposition on graphite. In contrast, the interlayer on SiO decreases work function of SiO surface, which promotes the formation of inorganic SEI on SiO. Hence the degradation of SEI is suppressed with LiIn layer at SiO electrode. This leads to a reduction in the ongoing accumulation of SEI, thereby enhancing durability of LIBs.

Theoretical and electrochemical analysis of halogenated salmphen-type dinuclear copper(II) complex: The influence of halogenated ligands on bandgap

The predictable control of energy levels in coordination polymer is an essential issue in molecular science. To explore a simple and feasible strategy for tuning the energy levels of Schiff base materials, the present work synthesized a novel halogen-substituted cofacial Schiff base compound, CuII2(2-Cl-Salmphen)2 (Cu-2-Cl-Salmphen), and the non-halogenated analogue CuII2(H-Salmphen)2 (Cu-H-Salmphen) was introduced for comparison. Experimental results show that the introduction of halogen atoms can effectively increase the absorbance and decrease the impedance of the compound. Further theoretical analyses revealed that the substitutional halogen atoms can not only enlarge the conjugation area but also change the electron density and the molecular orbital energy levels, thus enabling modulation of the bandgap values of the compounds. Besides, NCI studies have demonstrated that the substitution of halogens can form additional intermolecular interaction pathways, adjusting the interactions between adjacent molecules.

Terpolymer Containing a meta-Octyloxy-phenyl-Modified Dithieno[3,2-f:2',3'-h]quinoxaline Unit Enabling Efficient Organic Solar Cells.

With the rapid development of small-molecule electron acceptors, polymer electron donors are becoming more important than ever in organic photovoltaics, and there is still room for the currently available high-performance polymer donors. To further develop polymer donors with finely tunable structures to achieve better photovoltaic performances, random ternary copolymerization is a useful technique. Herein, by incorporating a new electron-withdrawing segment 2,3-bis(3-octyloxyphenyl)dithieno[3,2-f:2',3'-h]quinoxaline derivative (C12T-TQ) to PM6, a series of terpolymers were synthesized. It is worth noting that the introduction of the C12T-TQ unit can deepen the highest occupied molecular orbital energy levels of the resultant polymers. In addition, the polymer Z6 with a 10% C12T-TQ ratio possesses the highest film absorption coefficient (9.86 × 104 cm-1) among the four polymers. When blended with Y6, it exhibited superior miscibility and mutual crystallinity enhancement between Z6 and Y6, suppressed recombination, better exciton separation and charge collection characteristics, and faster hole transfer in the D-A interface. Consequently, the device of Z6:Y6 successfully achieved enhanced photovoltaic parameters and yielded an efficiency of 17.01%, higher than the 16.18% of the PM6:Y6 device, demonstrating the effectiveness of the meta-octyloxy-phenyl-modified dithieno[3,2-f:2',3'-h]quinoxaline moiety to build promising terpolymer donors for high-performance organic solar cells.

Investigating Cathode Electrolyte Interphase Formation in NMC 811 Primary Particles through Advanced 4D-STEM ACOM Analysis

Investigating Cathode Electrolyte Interphase Formation in NMC 811 Primary Particles through Advanced 4D-STEM ACOM Analysis

Aqueous Processed All-Polymer Solar Cells with High Open-Circuit Voltage Based on Low-Cost Thiophene-Quinoxaline Polymers.

Eco-friendly solution processing and the low-cost synthesis of photoactive materials are important requirements for the commercialization of organic solar cells (OSCs). Although varieties of aqueous-soluble acceptors have been developed, the availability of aqueous-processable polymer donors remains quite limited. In particular, the generally shallow highest occupied molecular orbital (HOMO) energy levels of existing polymer donors limit further increases in the power conversion efficiency (PCE). Here, we design and synthesize two water/alcohol-processable polymer donors, poly[(thiophene-2,5-diyl)-alt-(2-((13-(2,5,8,11-tetraoxadodecyl)-2,5,8,11-tetraoxatetradecan-14-yl)oxy)-6,7-difluoroquinoxaline-5,8-diyl)] (P(Qx8O-T)) and poly[(selenophene-2,5-diyl)-alt-(2-((13-(2,5,8,11-tetraoxadodecyl)-2,5,8,11-tetraoxatetradecan-14-yl)oxy)-6,7-difluoroquinoxaline-5,8-diyl)] (P(Qx8O-Se)) with oligo(ethylene glycol) (OEG) side chains, having deep HOMO energy levels (∼-5.4 eV). The synthesis of the polymers is achieved in a few synthetic and purification steps at reduced cost. The theoretical calculations uncover that the dielectric environmental variations are responsible for the observed band gap lowering in OEG-based polymers compared to their alkylated counterparts. Notably, the aqueous-processed all-polymer solar cells (aq-APSCs) based on P(Qx8O-T) and poly[(N,N'-bis(3-(2-(2-(2-methoxyethoxy)-ethoxy)ethoxy)-2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-methyl)propyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-(2,5-thiophene)] (P(NDIDEG-T)) active layer exhibit a PCE of 2.27% and high open-circuit voltage (VOC) approaching 0.8 V, which are among the highest values for aq-APSCs reported to date. This study provides important clues for the design of low-cost, aqueous-processable polymer donors and the fabrication of aqueous-processable OSCs with high VOC.

Efficient triisopropylsilylethynyl-substituted benzo[1,2-b:4,5-b′]dithiophene-based random terpolymers enable non-fullerene organic solar cells with enhanced efficiency

Recent work has highlighted the pivotal role of ternary random polymers in the development of efficient high-performance polymer donors for organic solar cells (OSCs) and most of these D-A copolymer donors are so far constituted of an equal proportion of D and A-units. In this contribution, we report series of PM6-based ternary random terpolymers with unequal D- and A-units, namely, PM-TIPS10, PM-TIPS20 and PM-TIPS20, respectively by adding the 10%, 20% and 30% of simple and low-cost triisopropylsilylethynyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-TIPS) unit as second donor (D1) unit in polymer backbone based on D1-A-D2-A molecular design. Ascribed from the structural similarity of the two building blocks in the terpolymer backbone, these polymers showed orderly molecular packing, broadened light absorption, and the face-on orientation of the active layer to facilitate charge transport. Additionally, the new polymers displayed much deeper highest occupied molecular orbital (HOMO) energy levels than host PM6 polymer, which helped in enhancing the open circuit voltage (Voc) in the PM-TIPS-based OSCs. As a result, when combined with BTP-eC9 acceptor unit, PM-TIPS10 and PM-TIPS20 displayed best efficiency of 16.7 and 16.5% with a small energy loss of 0.484 and 0.473 eV, producing overall superior device parameters compared to PM6-based devices tested parallelly (PCE of 15.7%). This study reveals the correlation between introduction of the BDT-TIPS unit on polymer properties and photovoltaic performance and thus contributes to the design of high-PCE polymer donors by adapting a ternary random copolymerization strategy.

Enhancing Comprehensive Performance via Capturing and Scattering the Carriers inside PESU-Based Nanocomposite Film Capacitors.

Film capacitors have become key electronic components for electrical energy storage installations and high-power electronic systems. Nonetheless, high-temperature and high-electric-field environments would cause a surge of the energy loss, placing a fundamental challenge for film capacitors applied in harsh environments. Here, we constructed a composite film, combining poly(ether sulfone) (PESU) with excellent thermal stability and large-band-gap filler boron nitride nanosheets (BNNSs). The introduction of BNNSs would form deep/shallow traps inside the dielectric polymer matrix, effectively affecting charge migration. Via density functional theory (DFT) calculation, the higher highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the BNNS than the matrix facilitate scattering electrons and attracting holes. The resultant composite obtains the desired discharged energy densities (Ud) of 5.89 and 3.86 J/cm3 accompanied by an efficiency above 90% at 150 and 200 °C, respectively, surpassing those of existing dielectric materials at the high-temperature conditions. The paper provides a promising composite dielectric material for high-performance film capacitors capable of operating in harsh environments.