Lowest Unoccupied Molecular Orbital Levels Research Articles

Exploring Chlorinated Solvents as Electrolytes for Lithium Metal Batteries: A DFT and MD Study

ABSTRACTElectrolytes with fluorinated solvents have been regarded as a promising strategy to stabilize high‐voltage cathodes and the interphase of lithium anode in lithium metal batteries (LMBs). However, the rigorous synthesis approach and high cost have led to a demand for developing cost‐effective solvents with suitable properties for LMBs. Herein, we explored the possibility of using chlorinate solvents as electrolytes using density functional theory (DFT) and classical molecular dynamics (MD) simulation. Taking ether (1,2‐dimethoxyethane [DME], 1,3‐dioxolane [DOL]), carbonate (dimethyl carbonate [DMC], and ethylene carbonate [EC]) as examples, we first compared the energy variation of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) upon Cl and F substitution. In particular, we found that 1,2‐bis(chloromethoxy)ethane (DME‐2Cl‐2) has the lowest HOMO and the highest LUMO level among the chlorinated DME after coordinating with Li+, enabling a potentially wide voltage stability. Further MD simulation reveals that lithium ions in DME‐2Cl‐2 has a weaker solvation coordination with solvents but stronger interaction with anions than DME and 1,2‐bis(Fluoromethoxy)ethane (DME‐2F‐2), which is more beneficial for forming stable anion‐derived solid electrolyte interphase (SEI). Our findings suggest that chlorinated solvents can be used as promising electrolytes for LMBs.

Accurate molecular recognition from the lowest unoccupied molecular orbital

The quantification of the lowest unoccupied molecular orbital level (LUMO) for molecular semiconductors is of great importance, because it determines the charge transport process and hence the performances of diverse electronic devices. Unfortunately, there is always lack of a convenient technique to determine the intrinsic LUMO. This work provides a reliable electrical spectroscopy by employing an easy-operating hot electron transistor, to make an accurate measurement. By taking advantage of a novel method, named the first derivative-assisted linear fitting method, the determination of the intrinsic LUMO becomes more scientific. Here, four kinds of molecular semiconductors are selected as the research objects and the values can be precisely decided even with a quite small difference in LUMO, which demonstrate the universality and the accuracy of our method. As expected, all the measured values are highly repeatable and it further confirms that we have provided a practical technique for the LUMO detection.

Novel integrated reference-counter electrode for electrochemical measurements of HOMO and LUMO levels in small-molecule thin-film semiconductors for OLEDs

Organic light-emitting diodes (OLEDs) are a prominent display technology, yet the accurate characterization of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels in their constituent materials remains challenging. This study introduces a novel integrated reference-counter electrode (IRCE) assembly, leveraging a gel polymer electrolyte with an embedded silver quasi-reference electrode, facilitating the electrochemical measurement of HOMO and LUMO levels in small molecular thin-film semiconductors. Calibration of the IRCE against ferrocene enables the establishment of an absolute energy scale. Comparative stability tests against a standard Ag/AgNO3 reference electrode confirm the IRCE's reliability. Electrochemical characterization using cyclic voltammetry was performed on prototypical OLED materials, including NPB, TCTA, PO-T2T neat films, and an NPB:PO-T2T exciplex film. While NPB and PO-T2T exhibited stable voltammograms, TCTA showed signs of electropolymerization. Additionally, the HOMO level of the NPB:PO-T2T exciplex was slightly shifted compared to that of NPB, suggesting interactions within the exciplex. The results demonstrated the IRCE's capability to accurately determine frontier energy levels in thin films, paving the way for better device modeling and a better understanding of underlying electronic processes in organic semiconductors.

Improving the performance of organic solar cell via tuning the interfacial n-doping of cathode-modifying layer

Organic solar cells have been fabricated using thermally evaporated bathocuproine (BCP) and ytterbium n-doped BCP (BCP:Yb) to modify the interfaces of active layer and cathode. The device with 10 nm BCP presents open-circuit voltage of 0.791 V and fill factor of 0.670, greater than those (0.785 V and 0.636) of the device with 10 nm BCP:Yb, mostly due to that the BCP:Yb causes severe nonradiative recombination in active layer. The device with 1 nm BCP/9 nm BCP:Yb offers open-circuit voltage of 0.793 V, almost same as that of the device with 10 nm BCP, due to the two following reasons. Firstly, the interlayer of 1 nm BCP is able to separate active layer from BCP:Yb, thereby preventing the nonradiative recombination. Secondly, the BCP interlayer is so thin that the interfacial n-doping of Yb in it raises the Fermi level close to its lowest unoccupied molecular orbital level, whereby it forms ohmic contacts with active layer and BCP:Yb. Despite showing decreased fill factors, the devices with 10 nm BCP:Yb and 1 nm BCP/9 nm BCP:Yb give short-circuit current densities of 15.43 and 15.62 mA cm−2, respectively, larger than that (14.47 mA cm−2) of the device with 10 nm BCP. The power conversion efficiency based on 1 nm BCP/9 nm BCP:Yb is 8.11 %, higher than those based on 10 nm BCP (7.67 %) and 10 nm BCP:Yb (7.71 %). The current research indicates that tuning the interfacial n-doping of cathode-modifying layers is a facial and effective method to improve the performance of organic solar cells.

Photo-Modulation of Atomically Thin Molybdenum Diselenides Functionalized with Photochromic Molecules

Two-dimensional (2D) transition metal dichalcogenide semiconductors have garnered significant attention due to their extraordinary electrical and optical properties. It has been increasingly important to develop strategies for modulating their properties. A number of methods have been introduced, including doping, electric and magnetic fields, mechanical strain, etc. Herein, we report a novel approach of using photochromic molecules to modulate optoelectronic properties of monolayer MoSe2 with light. We have synthesized photochromic diarylethene (DAE) molecules that can switch between two isomeric forms, referred to as open and closed, under UV and visible light, respectively. The DAE molecules formed a uniform layer with a thickness of approximately 2 nm on monolayer MoSe2. Our density functional theory (DFT) calculations suggest that the TMD and DAE will align their band energy levels such that UV irradiation moves the lowest unoccupied molecular orbital (LUMO) energy of DAE in between the conduction band minimum (CBM) and valence band minimum (VBM) of MoSe2. This will facilitate photoexcited electron transfer from MoSe2 to DAE LUMO. Experimentally, we have confirmed our predictions by observing a strong quenching of photoluminescence (PL) and an increase of electrical conductivity in MoSe2. In contrast, visible light induced isomerization to the open form of DAE and expanded its energy levels, moving the LUMO level above the MoSe2 CBM. Therefore, the PL was retained and there was no significant change in electrical conductivity. We showed that this photoswitching can dynamically modulate the optoelectronic properties by demonstrating multiple cycles of PL emission and quenching, by alternating UV and visible light repeatedly. Lastly, our Kelvin probe force microscopy (KPFM) revealed that the potential of MoSe2 monolayers can also be modulated with photochromic molecules and external light irradiation. Our work elucidates photo-processes and exciton mechanisms at the hybrid interfaces and lays the foundation for novel applications including new phototransistors and other 2D optoelectronic devices.

Incorporating Zinc Metal Sites in Aluminum-Coordinated Porphyrin Metal-Organic Frameworks for Enhanced Photocatalytic Nitrogen Reduction to Ammonia.

Rationally designing photocatalysts is crucial for the solar-driven nitrogen reduction reaction (NRR) due to the stable N≡N triple bond. Metal-organic frameworks (MOFs) are considered promising candidates but suffer from insufficient active sites and inferior charge transport. Herein, it is demonstrated that incorporating 3d metal ions, such as zinc (Zn) or iron (Fe) ions, into Al-coordinated porphyrin MOFs (Al-PMOFs) enables the enhanced ammonia yield of 88.7 and 65.0µggcat -1h-1, 2.5- and 1.8-fold increase compared to the pristine Al-PMOF (35.4µggcat -1h-1), respectively. The origin of ammonia (NH3) is verified via isotopic labeling experiments. Incorporating Zn or Fe into Al-PMOF generates active sites in Al-PMOF, that is, Zn-N4 or Fe-N4 sites, which not only facilitates the adsorption and activation of N2 molecules but suppresses the charge recombination. Photophysical and theoretical studies further reveal the upshift of the lowest unoccupied molecular orbital (LUMO) level to a more energetic position upon inserting 3d metal ions (with a more significant shift in Zn than Fe). The promoted nitrogen activation, suppressed charge recombination, and more negative LUMO levels in Al-PMOF(3d metal) contribute to a higher photocatalytic activity than pristine Al-PMOF. This work provides a promising strategy for designing photocatalysts for efficient solar-to-chemical conversion.

Insight into Fluoride Additives to Enhance Ammonia Production from Lithium-Mediated Electrochemical Nitrogen Reduction Reaction.

Demands for green ammonia production increase due to its application as a proton carrier, and recent achievements in electrochemical Li-mediated nitrogen reduction reactions (Li-NRRs) show promising reliability. Here, it is demonstrated that F-containing additives in the electrolyte improve ammonia production by modulating the solid electrolyte interphase (SEI). It is suggested that the anionic additives with low lowest unoccupied molecular orbital levels enhance efficiency by contributing to the formation of a conductive SEI incorporated with LiF. Specifically, as little as 0.3wt.% of BF4 - additive to the electrolyte, the Faradaic efficiency (FE) for ammonia production is enhanced by over 15% compared to an additive-free electrolyte, achieving a high yield of 161 ± 3nmol s-1 cm-2. The BF4 - additive exhibits advantages, with decreased overpotential and improved FE, compared to its use as the bulk electrolyte. The observation of the Li3N upper layer implies that active Li-NRR catalytic cycles are occurring on the outermost SEI, and density functional theory simulations propose that an SEI incorporated with LiF facilitates energy profiles for the protonation by adjusting the binding energies of the intermediates compared to bare copper. This study unlocks the potential of additives and offers insights into the SEIs for efficient Li-NRRs.

Mitigating PTFE decomposition in ultra thick dry-processed anodes for high energy density lithium-ion batteries

Dry electrode technology is a next-generation method for manufacturing lithium-ion batteries because it is useful for fabricating thick electrodes without solvents, facilitating high energy densities and cutting down on the battery manufacturing costs. However, the commonly used polytetrafluoroethylene (PTFE) binder in dry electrode technology undergoes severe decomposition in dry-processed anodes during the first lithiation process due to its low lowest unoccupied molecular orbital level. This phenomenon seriously aggravates battery performance, such as in terms of the initial coulombic efficiency and cycle life. Thus, a strategy to suppress this irreversible reaction of PTFE should be established for dry-processed anodes to increase the energy density of LIBs without adverse effects on battery performance. To address this challenge, in this work, fluoroethylene carbonate (FEC) as an electrolyte additive has been introduced to form a preemptive and stable FEC-derived solid electrolyte interface (SEI) to protect a graphite and the PTFE binder. This SEI considerably alleviates the irreversible reaction of PTFE, thereby securing the reversible capacity and maintaining the structure of the electrode through the great binding properties. These results provide guidance for increasing the electrochemical stability in dry-processed anode systems, which gets closer the innovative dry anode technology for cost-effectiveness and high energy density.

Design Principles of Quinone Redox Systems for Advanced Sulfide Solid-State Organic Lithium Metal Batteries.

The emergence of solid-state battery technology presents a potential solution to the dissolution challenges of high-capacity small molecule quinone redox systems. Nonetheless, the successful integration of argyrodite-type Li6PS5Cl, the most promising solid-state electrolyte system,and quinone redox systems remains elusive due to their inherent reactivity. Here, a library of quinone derivatives is selected as model electrode materials to ascertain the critical descriptors governing the (electro)chemical compatibility and subsequently the performances of Li6PS5Cl-based solid-state organic lithium metal batteries (LMBs). Compatibility is attained if the lowest unoccupied molecular orbital level of the quinone derivative is sufficiently higher than the highest occupied molecular orbital level of Li6PS5Cl. The energy difference is demonstrated to be critical in ensuring chemical compatibility during composite electrode preparation and enable high-efficiency operation of solid-state organic LMBs. Considering these findings, a general principle is proposed for the selection of quinone derivatives to be integrated with Li6PS5Cl, and two solid-state organic LMBs, based on 2,5-diamino-1,4-benzoquinone and 2,3,5,6-tetraamino-1,4-benzoquinone, are successfully developed and tested for the first time. Validating critical factors for the design of organic battery electrode materials is expected to pave the way for advancing the development of high-efficiency and long cycle life solid-state organic batteries based on sulfides electrolytes.

Side chain-engineered pseudocapacitive semiconducting polymer electrodes for symmetrical supercapacitors operable at wide potentials

Pseudocapacitive electrodes based on inorganic metal oxides exhibit superior capacitance. However, they suffer from limited operational voltage, resulting in low energy and power densities. To address these issues, redox semiconducting polymer (SP)-based pseudocapacitive electrodes, integrating electron donor and acceptor functionalities, offer a promising solution. In this study, we introduce two novel pseudocapacitive SP electrodes composed of highly planar electron-donating building blocks 4,8-bis ((5-octylthiophen-2-yl)ethynyl)benzo[1,2-b:4,5-b'] dithiophene (TBDT) with an electron-accepting building blocks benzo[c][1,2,5]thiadiazole (BT) and its side chain manipulated counterpart, i.e., OBT, denoted as SP1 and SP2, respectively. Among them, SP2 demonstrates a maximum specific capacitance of 117 F/g at 1 A/g. Furthermore, a symmetric supercapacitor fabricated for full-cell applications exhibits a significant energy density, reaching 29.1 Wh kg−1, and a maximum power density of 12.4 kW kg−1 within the wide operating potential window of 2.5 V. The exceptional performance of the pseudocapacitive electrode can be attributed to its highly planar backbone, nanoporous morphology, low crystallinity, and low lowest unoccupied molecular orbital levels. Overall, this new class of pseudocapacitive polymer electrode holds great potential for diverse sustainable energy storage technologies, addressing the limitations of traditional inorganic metal oxide-based electrodes by offering wide potentials window.

Unexpected Electronic Features of NiO Quantum Dots Produced by Femtosecond Pulsed Laser Ablation in Water.

This study examines the effect of quantum confinement and surface orientations on the electronic properties of NiO quantum dots. It compares NiO nanocrystals produced via atmospheric-pressure microplasma and femtosecond laser (fs-laser) ablation in water, finding that both methods yield quantum-confined nanocrystals with a defined face-centered cubic lattice. Notably, fs-laser synthesis generates crystalline nanocrystals from both crystalline and amorphous targets. While the electronic properties, i.e., energy of the highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO), of microplasma-synthesized NiO nanocrystals are consistent with the literature, the electronic characteristics of NiO nanocrystals produced by a fs-laser, particularly the high-lying LUMO level, are unusual for NiO quantum dots. Supported by density functional theory calculations, we show that the observed level positions are related to the different polar and nonpolar faces of the nanocrystal surface.

Surfactant Composition Dependent Evolution of Electronic/Structural Properties of P3HT Nanoparticle Colloids Synthesized via Mini-Emulsion Technique

: This study investigates the influence of surfactant (sodium dodecyl sulfate, SDS) concentration on the size and optoelectronic properties of poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) synthesized via the mini-emulsion technique. P3HT NPs were fabricated with varying SDS concentrations. The size dependent optoelectronic properties, including the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels, were analyzed through photoelectron spectroscopy in air, UV-Vis absorption spectroscopy and cyclic voltammetry. A clear trend of decreasing NP size with increasing SDS concentration was observed. Higher SDS levels resulted in smaller NPs with enhanced pi-pi stacking and shorter conjugation lengths. This structural change led to a noticeable shift in HOMO and LUMO levels, indicating a direct correlation between surfactant concentration and the electronic properties of the P3HT NPs. The absorption spectra revealed a decrease in the A0-0/A0-1 ratio with smaller NP size, suggesting a transition towards more pronounced H-aggregate characteristics. As the size of the P3HT NPs decreases, there is a notable increase in H-aggregate formation. This increase can be attributed to enhanced interchain interactions between the polymer chains. In smaller NPs, the surface area-to-volume ratio is higher, leading to more significant interactions between adjacent polymer chains. These interactions promote the formation of H-aggregates, characterized by their interchain pi-pi stacking, which differs from the intrachain coupling observed in J-aggregates.

Photocatalytic activity in graded off-valent cations substituted NaNbO3

This study investigates the impact of off-valent doping on the photocatalytic properties of NaNbO3 concerning the degradation of Methylene Blue. Compositions with x values of 0.00 (representing pure NaNbO3, denoted as NBO) and 0.05 within the material system Na1-xAxNbO3 (where A is K1+, Ba2+, La3+, abbreviated as K-NBO, Ba-NBO, and La-NBO respectively) were synthesized using the conventional solid-state reaction method. The UV–visible analysis revealed a decrease in the band gap for samples K-NBO and Ba-NBO, while an increase was observed for sample La-NBO. Raman modes of lower wave numbers merged and shifted towards the higher wave number side. The determination of valence band edge and conduction band edge involved computational analysis based on XPS survey scans, and the band gap energy values were derived from UV–Visible spectroscopy results. Examining the band diagram of the samples (NBO, K-NBO, Ba-NBO, and La-NBO) in conjunction with the highest occupied molecular orbital and lowest unoccupied molecular orbital levels of MB dye provided insights into potential degradation mechanisms. Photocatalytic dye degradation experiments for Methylene Blue demonstrated that doping increased the degradation efficiency of samples K-NBO, Ba-NBO, and La-NBO compared to NBO. Among all NaNbO3 based prepared samples, Ba-NBO exhibited the highest degradation efficiency of 96%, however slightly less than the reference sample P25 TiO2.

Bis(benzoselenadiazol)ethane: A π‐Extended Acceptor‐Dimeric Unit for Ambipolar Polymer Transistors with Hole and Electron Mobilities Exceeding 10 cm2 V−1 s−1

AbstractThe lack of ambipolar polymers with balanced hole (μh) and electron mobilities (μe) >10 cm2 V−1 s−1 is the main bottleneck for developing organic integrated circuits. Herein, we show the design and synthesis of a π‐extended selenium‐containing acceptor‐dimeric unit, namely benzo[c][1,2,5]selenadiazol‐4‐yl)ethane (BBSeE), to address this dilemma. In comparison to its sulfur‐counterpart, BBSeE demonstrates enlarged co‐planarity, selective noncovalent interactions, polarized Se−N bond, and higher electron affinity. The successful stannylation of BBSeE offers a great opportunity to access acceptor‐acceptor copolymer pN‐BBSeE, which shows a narrower band gap, lower‐lying lowest unoccupied molecular orbital level (−4.05 eV), and a higher degree of backbone planarity. Consequently, the pN‐BBSeE‐based organic transistors display an ideally balanced ambipolar transporting property with μh and μe of 10.65 and 10.72 cm2 V−1 s−1, respectively. To the best of our knowledge, the simultaneous μh/μe values >10.0 cm2 V−1 s−1 are the best performances ever reported for ambipolar polymers. In addition, pN‐BBSeE shows an excellent shelf‐storage stability, retaining over 85 % of the initial mobility values after two months storage. Our study demonstrates the π‐extended acceptor‐dimeric BBSeE is a promising acceptor building block for constructing high‐performance ambipolar polymers applied in next‐generation organic integrated circuit.

Bis(benzoselenadiazol)ethane: A π-Extended Acceptor-Dimeric Unit for Ambipolar Polymer Transistors with Hole and Electron Mobilities Exceeding 10 cm2 V-1 s-1.

The lack of ambipolar polymers with balanced hole (μh) and electron mobilities (μe) >10 cm2 V-1 s-1 is the main bottleneck for developing organic integrated circuits. Herein, we show the design and synthesis of a π-extended selenium-containing acceptor-dimeric unit, namely benzo[c][1,2,5]selenadiazol-4-yl)ethane (BBSeE), to address this dilemma. In comparison to its sulfur-counterpart, BBSeE demonstrates enlarged co-planarity, selective noncovalent interactions, polarized Se-N bond, and higher electron affinity. The successful stannylation of BBSeE offers a great opportunity to access acceptor-acceptor copolymer pN-BBSeE, which shows a narrower band gap, lower-lying lowest unoccupied molecular orbital level (-4.05 eV), and a higher degree of backbone planarity. Consequently, the pN-BBSeE-based organic transistors display an ideally balanced ambipolar transporting property with μh and μe of 10.65 and 10.72 cm2 V-1 s-1, respectively. To the best of our knowledge, the simultaneous μh/μe values >10.0 cm2 V-1 s-1 are the best performances ever reported for ambipolar polymers. In addition, pN-BBSeE shows an excellent shelf-storage stability, retaining over 85 % of the initial mobility values after two months storage. Our study demonstrates the π-extended acceptor-dimeric BBSeE is a promising acceptor building block for constructing high-performance ambipolar polymers applied in next-generation organic integrated circuit.

Bifunctional Urea–Polyethyleneimine‐Mediated Surface Engineering in SnO2 Electron‐Transport Layer for Efficient and Stable Organic Solar Cells

Because of its high conductivity, wide bandgap, and excellent photostability, tin oxide (SnO2) has long been recognized as an electron‐transport layer (ETL) in organic solar cells (OSCs). However, the energy‐level mismatch between the work function (WF) of SnO2 and the lowest unoccupied molecular orbital level of Y‐series nonfullerene acceptors (NFAs), along with the abundance of surface defects on SnO2, have limited its widespread application as ETLs in OSCs. Herein, a novel approach utilizing urea‐functionalized polyethyleneimine (PEI) materials called u‐PEIs for modifying SnO2 is introduced. This modification, which serves dual purposes of WF modulation and surface‐defect passivation, can mitigate the energy barriers of SnO2/Y‐series NFA and increase the conductivity of the SnO2 film. PM6:Y6‐based OSCs with u‐PEI‐modified SnO2 (SnO2:u‐PEI) ETLs exhibit a remarkable efficiency of 16%, which significantly exceeds that (13.5%) achieved with bare SnO2‐based OSCs, along with outstanding photo‐ and thermal stability. This study confirms the efficacy of urea‐functionalized PEI for efficient and stable OCSs, paving the way for SnO2 applications.

Design of Chlorinated Indaceno[1,2-b:5,6-b']dithiophene Acceptors toward Efficient Organic Photovoltaics.

Chlorinated modifications have been extensively employed to modulate the optoelectronic properties of π-conjugated materials. Herein, the Cl substitution in designing nonfullerene acceptors (NFAs) with various bandgaps is studied. Four narrow-bandgap electron acceptors (GS-40, GS-41, GS-42, and GS-43) were synthesized by tuning the electrostatic potential distributions of the molecular conjugated backbones. The optical absorption onset of these NFAs ranges from 900 to 1030 nm. Compared to the nonchlorinated analogue, the introduction of Cl atoms on the core of indaceno[1,2-b:5,6-b'] dithiophene (IDT) and π spacer results in an upward shift of the lowest unoccupied molecular orbital levels and induces a blue shift in the absorption spectra of the NFAs. This alteration facilitates achieving appropriate energy-level alignment and favorable bulk heterojunction morphology when blended with the widely used donor PBDB-TF. The PBDB-TF:GS-43-based solar cells show an optimal power conversion efficiency of 13.3%. This work suggests the potential of employing chlorine-modified IDT and thiophene units as fundamental building blocks for developing high-performance photoactive materials.

Improved Capacitive Energy Storage at High Temperature via Constructing Physical Cross‐Link and Electron–Hole Pairs Based on P‐Type Semiconductive Polymer Filler

AbstractIn this work, p‐type polymer semiconductor poly(2‐((3,6,7,10,11‐pentakis (hexyloxy) triphenylene‐2‐yl)oxy)ethyl methacrylate) (PMHT) is added into polyetherimide (PEI). Benefiting from the electrostatic interaction between strong electrophilic charged phenyls of the PEI matrix and strong electronegative benzophenanthrene unit of the PMHT filler, the physical cross‐linked networks are formed in polymer blends. Meanwhile, the lowest unoccupied molecular orbital level of PEI is close to the highest occupied molecular orbital level of PMHT, which is easy to establish electron–hole pair by Coulomb force. Thus, the carrier trap is constructed in the heterojunction region between PMHT filler and PEI matrix. Both physically cross‐linked networks and electron–hole pairs can promote breakdown strength (Eb) of PEI and decrease energy loss. Importantly, PMHT filler can improve the dielectric constant of PEI. As a result, 0.75 wt% PMHT/PEI delivers an ultrahigh discharge energy density (Ud) of 10.7 J cm−3 at an Eb of 680 MV m−1 and at room temperature, and maintains a charge and discharge efficiency of above 90%. In addition, a superior Ud of 5.1 and 3.3 J cm−3 is achieved at 150 and 200 °C, respectively. This paper creates a new perspective for preparing high‐properties polymer dielectrics by combining the advantages of cross‐linking and electron–hole pairs.

Lifetime enhancement in QDLEDs via an electron-blocking hole transport layer

This study investigates the impact of an engineered hole transport layer (HTL) on the stability of electroluminescent quantum dot light-emitting devices (QDLEDs). The 9-Phenyl-3,6-bis(9-phenyl-9Hcarbazol-3-yl)-9H-carbazole (Tris-PCz) HTL, which possesses a shallower lowest unoccupied molecular orbital (LUMO) energy level compared to the widely used 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) HTL, is employed to confine electron overflow toward the HTL. Utilizing the Tris-PCz HTL results in a 20× improvement in the electroluminescence half-life (LT50) of QDLEDs compared with conventional QDLEDs using the CBP HTL. Electric and optoelectronic analyses reveal that the migration of excess electrons toward the HTL is impeded by the up-shifted LUMO level of Tris-PCz, contributing to prolonged operational device stability. Furthermore, the augmented electric field at the QD/Tris-PCz interface, due to accumulated electrons, expedites hole injection rates, leading to better charge injection balance and the confinement of the exciton recombination zone within the QD and thus the device stability enhancement. This study highlights the significant influence of the HTL on QDLED stability and represents one of the longest LT50 for a QDLED based on the conventional core/shell QD structure.

Effect of fluorine substitution on the electronic states and conductance of CuPc on Cu(100)

The electronic states and conductance of CuPc, F8CuPc, and F16CuPc on Cu(100) were studied by using scanning tunneling microscopy (STM) and the density functional theory (DFT) calculations. For all molecules, the lowest unoccupied molecular orbital (LUMO) was observed around the Fermi level (EF), regardless of the difference in the original LUMO levels of the free molecules. This indicates that the strong interaction causes the pinning of EF at LUMO levels. Meanwhile, the differential conductance at EF is drastically affected by the substitution: it increases and decreases for CuPc and F16CuPc, respectively, suggesting that the Fano effect plays a major role in the conductance. This finding provides a new strategy for the control of molecular conductance by chemical substitution.