Electronic Structure of Carbazole-Based Phosphine Oxides as Ambipolar Host Materials for Deep Blue Electrophosphorescence: A Density Functional Theory Study

We report the results of Density Functional Theory calculations on a series of carbazole-based phosphine oxides that experimental data have shown to be promising ambipolar host molecules for deep blue electrophosphorescence. The hosts under investigation contain either 1, 2, or 3 carbazole subunits attached to the phenyl rings of a triphenylphosphoryl group, with the carbazoles acting as hole transporters/acceptors and the triphenylphosphoryl groups as electron transporters/acceptors. The results underline that, in addition to the strong inductive effect of the phosphoryl groups, the LUMO of these hosts is further stabilized by the molecular orbital interactions among the phenyl rings of the triphenylphosphoryl group, which is modulated by the electron-withdrawing inductive effects of the carbazole subunits. The lowest triplet state of the hosts correspond to localized transitions within the carbazole units, which leads to a high triplet energy on the order of 3 eV. We describe the important buffer role of the phenyl rings in preventing the phosphoryl moiety from negatively affecting the hole-accepting characteristics and high triplet energies of the carbazole units

Prediction of Remarkable Ambipolar Charge-Transport Characteristics in Organic Mixed-Stack Charge-Transfer Crystals

We have used density functional theory calculations and mixed quantum/classical dynamics simulations to study the electronic structure and charge-transport properties of three representative mixed-stack charge-transfer crystals, DBTTF–TCNQ, DMQtT–F₄TCNQ, and STB–F₄TCNQ. The compounds are characterized by very small effective masses and modest electron–phonon couplings for both holes and electrons. The hole and electron transport characteristics are found to be very similar along the stacking directions; for example, in the DMQtT–F₄TCNQ crystal, the hole and electron effective masses are as small as 0.20 and 0.26 <i>m</i>₀, respectively. This similarity arises from the fact that the electronic couplings of both hole and electron are controlled by the same superexchange mechanism. Remarkable ambipolar charge-transport properties are predicted for all three crystals. Our calculations thus provide strong indications that mixed-stack donor–acceptor materials represent a class of systems with high potential in organic electronics

An <i>in Situ</i> Formed Multifunctional Interphase with High Dendrite Tolerance for Long-Life Solid-State Sodium–Metal Batteries

The development of practical solid-state sodium–metal batteries calls for simple but efficient solutions to overcome poor anode||electrolyte compatibility. Here, we for the first time, design an interphase comprised of NaCl, Sn, and Na–Sn alloy formed in situ at room temperature to stabilize the Na||Na3Zr2Si2PO12 interface. Equipped with the dynamically stable, low-impedance, and dendrite-free interface, the symmetric cells demonstrate a 31-fold reduction in interfacial resistance, a high critical current density to 0.8 mA cm–2, along with a 1000-h cyclability at 25 °C. The corresponding Na||Na3V2(PO4)3 full cells showcase a capacity retention rate of 93% after 1071 cycles at 0.5 C

An <i>in Situ</i> Formed Multifunctional Interphase with High Dendrite Tolerance for Long-Life Solid-State Sodium–Metal Batteries

The development of practical solid-state sodium–metal batteries calls for simple but efficient solutions to overcome poor anode||electrolyte compatibility. Here, we for the first time, design an interphase comprised of NaCl, Sn, and Na–Sn alloy formed in situ at room temperature to stabilize the Na||Na3Zr2Si2PO12 interface. Equipped with the dynamically stable, low-impedance, and dendrite-free interface, the symmetric cells demonstrate a 31-fold reduction in interfacial resistance, a high critical current density to 0.8 mA cm–2, along with a 1000-h cyclability at 25 °C. The corresponding Na||Na3V2(PO4)3 full cells showcase a capacity retention rate of 93% after 1071 cycles at 0.5 C

Electronic Properties of Mixed-Stack Organic Charge-Transfer Crystals

The electronic structures of a series of donor–acceptor mixed-stack crystals have been investigated by means of density functional theory calculations. The results highlight that a number of the donor–acceptor crystals under consideration are characterized by wide valence and conduction bands, large hole and electron electronic couplings, and as a result very low hole and electron effective masses. The fact that the effective masses and electronic couplings for holes and electrons are nearly equal along the stacking directions implies that the hole and electron mobilities in these systems are also similar. In addition, in several of these crystals, charge transport has a two-dimensional character. The impact on the charge transport properties of the electronic couplings between donor and acceptor frontier orbitals and of the related energy gaps is also discussed

Naphtho[1,2-b:5,6‑<i>b</i>′]dithiophene Based Two-Dimensional Conjugated Polymers for Highly Efficient Thick-Film Inverted Polymer Solar Cells

Two-dimensional conjugated zigzag naphthodithiophene was used for construction of novel polymer photovoltaic materials. Two novel copolymers based on zigzag naphthodithiophene and alkylthieno­[3,4-<i>c</i>]­pyrrole-4,6-dione inserted with different alkyl substituted thiophene as bridges have been designed and synthesized (PzNDTT-TPD1 and PzNDTT-TPD2, respectively). The best power conversion efficiency of a PzNDTT-TPD1-based device reaches 7.50% at an active layer thickness of 203 nm and the device performances of PzNDTT-TPD1-based polymer solar cells are all above 6.4% with active layer thickness variations from 141 to 244 nm, suggesting that it is very suitable for the fabrication of high performance, large area solution-processed polymer solar cells

Electronic and Charge-Transport Properties of the Au₃(CH₃NCOCH₃)₃ Crystal: A Density Functional Theory Study

Density functional theory was used to investigate the electronic and charge-transport properties of the trinuclear gold Au₃(CH₃NCOCH₃)₃ crystal. Hole transport is found to be anisotropic and characterized by a very small effective mass of about 0.21 <i>m</i>₀ along the stacking direction of the Au₃ molecules. Interestingly, the calculations suggest an isotropic character of electron transport, for which the effective mass is about 1 <i>m</i>₀. We show that while the interstack interactions facilitate electron transport in the directions perpendicular to the stacks, they act to diminish this transport along the stacking directions. Overall, the present results indicate that this compound is a promising ambipolar material for application in electronic devices

Rationalization of the Selectivity in the Optimization of Processing Conditions for High-Performance Polymer Solar Cells Based on the Polymer Self-Assembly Ability

Tailoring the blend morphology in a bulk heterojunction device is of critical importance but remains a challenge today. Although the morphologies of polymer solar cells can be tuned by thermal/solvent annealing or by incorporation of solvent additives, optimizing the morphology of the active layer for a newly synthesized polymer has, to date, remained mostly an empirical approach. In this work, three typical polymers in organic photovoltaics have been studied. By processing at different conditions, each polymer reveals high selectivity in the optimizing methods. Optical spectrum and electrostatic force microscopy results demonstrate morphology as the main reason for various device performances. Further, these can be traced back to the self-assembly behaviors of polymers. By the established relationships between molecular structure, morphology, and the corresponding device performances, we propose a self-assembly based process-selection guideline for efficient performance improvement of newly synthesized materials

Highly Effective and Low-Cost MicroRNA Detection with CRISPR-Cas9

MicroRNAs have been reported as related to multiple diseases and have potential applications in diagnosis and therapeutics. However, detection of miRNAs remains improvable, given their complexity, high cost, and low sensitivity as of currently. In this study, we attempt to build a novel platform that detects miRNAs at low cost and high efficacy. This detection system contains isothermal amplification, detecting and reporting process based on rolling circle amplification, CRISPR-Cas9, and split-horseradish peroxidase techniques. It is able to detect trace amount of miRNAs from samples with mere single-base specificity. Moreover, we demonstrated that such scheme can effectively detect target miRNAs in clinical serum samples and significantly distinguish patients of non-small cell lung cancer from healthy volunteers by detecting the previously reported biomarker: circulating let-7a. As the first to use CRISPR-Cas9 in miRNA detection, this method is a promising approach capable of being applied in screening, diagnosing, and prognosticating of multiple diseases

From Alloy-Like to Cascade Blended Structure: Designing High-Performance All-Small-Molecule Ternary Solar Cells

Ternary blending strategy has been used to design and fabricate efficient organic solar cells by enhancing the short-circuit current density and the fill factor. In this manuscript, we report all-small-molecule ternary solar cells consisting of two compatible small molecules DR3TBDTT (<b>M1</b>) and DR3TBDTT-E (<b>M2</b>) as donors and PC₇₁BM as acceptor. A transformation from an alloy-like model to a cascade model are first realized by designing a novel molecule <b>M2</b>. It is observed that after thermal and solvent vapor annealing <b>M2</b> shifts from the mixed region to donor–acceptor (D–A) interfaces which ameliorates the charge transfer and recombination processes. The optimal ternary solar cells with 10% <b>M2</b> exhibited a power conversion efficiency of 8.48% in the alloy-like model and 10.26% in the cascade model. The proposed working mechanisms are fully characterized and further supported by the density functional theory and atomistic molecular dynamics simulations. This provides an important strategy to design high-performance ternary solar cells which contains one molecule not only is compatible with the main donor molecule but also performs a preference to appear at the D–A interfaces hence builds cascade energy levels