Hybrid nanorod-polymer solar cells

The Renaissance of Poly(3-hexylthiophene) as a Promising Hole-Transporting Material Toward Efficient and Stable Perovskite Solar Cells

To push the commercialization of the promising photovoltaic technique of perovskite solar cells (PSCs), the three-element golden law of efficiency, stability, and cost should be followed. As the key component of PSCs, hole-transporting materials (HTMs) involving widely-used organic semiconductors such as 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD) or poly(triarylamine) (PTAA) usually suffer high-cost preparation and low operational stability. Fortunately, the studies on the classical p-type polymer poly(3-hexylthiophene) (P3HT) as an alternative HTM have recently sparked a broad interest due to its low-cost synthesis, excellent batch-to-batch purity, superior hole conductivity as well as controllable and stable film morphology. Despite this, the device efficiency still lags behind P3HT-based PSCs mainly owing to the mismatched energy level and poor interfacial contact between P3HT and the perovskite layer. Hence, in this review, the study timely summarizes the developed strategies for overcoming the corresponding issues such as interface engineering, morphology regulation, and formation of composite HTMs from which some critical clues can be extracted to provide guidance for further boosting the efficiency and stability of P3HT-based devices. Finally, in the outlook, the future research directions either from the viewpoint of material design or device engineering are outlined.

Nanocomposite Photoanisotropic Materials for Applications in Polarization Holography and Photonics

Photoanisotropic materials, in particular azodyes and azopolymers, have attracted significant research interest in the last decades. This is due to their applications in polarization holography and 4G optics, enabling polarization-selective diffractive optical elements with unique properties, including circular polarization beam-splitters, polarization-selective bifocal lenses, and many others. Numerous methods have been applied to increase the photoinduced birefringence of these materials, and as a result, to obtain polarization holographic elements with a high diffraction efficiency. Recently, a new approach has emerged that has been extensively studied by many research groups, namely doping azobenzene-containing materials with nanoparticles with various compositions, sizes, and morphologies. The resulting nanocomposites have shown significant enhancement in their photoanisotropic response, including increased photoinduced birefringence, leading to a higher diffraction efficiency and a larger surface relief modulation in the case of polarization holographic recordings. This review aims to cover the most important achievements in this new but fast-growing field of research and to present an extensive comparative analysis of the result, reported by many research groups during the last two decades. Different hypotheses to explain the mechanism of photoanisotropy enhancement in these nanocomposites are also discussed. Finally, we present our vision for the future development of this scientific field and outline its potential applications in advanced photonics technologies.

The Bright and Enlightening Science of Quantum Dots

The 2023 Nobel Prize in Chemistry was awarded to Alexei Ekimov, Louis Brus, and Moungi Bawendi for the discovery and development of quantum dots, an area of research ripe with exciting results in terms of both fundamental science and present and forthcoming applications. Quantum dots, with their colors and their intriguing properties, have fascinated and engaged generations of scientists over the last 40 years, including myself. I present here a brief historical perspective of the field, from my personal standpoint and with insights from my own career, along with an outlook on what I believe will be the most interesting future developments in the field.

Synthesis and Characterization of Proton-Conducting Composites Prepared by Introducing Imidazole or 1,2,4-Triazole into AlPO-5 and SAPO-5 Molecular Sieves

The present work concerns proton-conducting composites obtained by replacing the water molecules present in aluminophosphate and silicoaluminophosphate AFI-type molecular sieves (AlPO-5 and SAPO-5) with azole molecules (imidazole or 1,2,4-triazole). Both the introduction of azoles and the generation of Brønsted acid centers by isomorphous substitution in aluminophosphate materials were aimed at improving the proton conductivity of the materials and its stability. In the presented study, AlPO-5 and several SAPO-5 materials differing in silicon content were synthesized. The obtained porous matrices were studied using PXRD, low-temperature nitrogen sorption, TPD-NH3, FTIR, and SEM. The proton conductivity of composites was measured using impedance spectroscopy. The results show that the increase in silicon content of the porous matrices is accompanied by an increase in their acidity. However, this does not translate into an increase in the conductivity of the azole composites. Triazole composites show lower conductivity and significantly higher activation energies than imidazole composites; however, most triazole composites show much higher stability. The different conductivity values for imidazole and triazole composites may be due to differences in chemical properties of the azoles.

Enhanced Interface Compatibility by Ionic Dendritic Molecules To Achieve Efficient and Stable Perovskite Solar Cells

Poly(3-hexylthiophene) (P3HT) represents a promising hole transport material for emerging perovskite solar cells (PSCs) due to its appealing merits of high thermal stability and appropriate hydrophobicity. Nonetheless, large energy losses at the P3HT/perovskite interface lead to unsatisfied efficiency and stability of the devices. Herein, two ionic dendritic molecules, 3,3'-(2,7-bis(3,6-bis(bis(4-methoxyphenyl)amino)-9H-carbazol-9-yl)-9H-fluorene-9,9-diyl)bis(N,N,N-trimethylpropan-1-aminium) iodide and 3,3'-(2,7-bis(bis(4-(bis(4-methoxyphenyl)amino)phenyl)amino)-9H-fluorene-9,9-diyl)bis(N,N,N-trimethylpropan-1-aminium) iodide, namely, MPA-Cz-FAI and MPA-PA-FAI, are rationally designed as the interlayer to enhance interfacial compatibility. The dendritic backbone with conjugated structure endows the hole transport layer with high conductivity, derived from the more ordered microstructure with larger crystallization and higher connectivity of domain zones. Besides, a better energy level alignment is established between P3HT and perovskite, which enhances the charge extraction and transport yield. In addition, the peripheral methoxy groups enable effective defect passivation at the interface to suppress nonradiative recombination and the quaternary ammonium iodide serving as side chains enable efficient interfacial hole extraction contributing to enhanced charge collection yield. As a result, the dopant-free P3HT-based PSCs modified with MPA-Cz-PAI deliver a champion efficiency of 19.7%, significantly higher than that of the control devices (15.4%). More encouragingly, the unencapsulated devices demonstrate competitive environmental stability by retaining over 85% of its initial efficiency after 1500 h of storage under humid conditions (70% relative humidity). This work provides an effective molecular design strategy for interface engineering, envisaging a bright prospect for the further development of efficient and stable perovskite solar cells.

The FP-LAPW/GAM-MPW1K approach: a reliable abinitio method for calculating the band gap of II-VI semiconductors monochalcogenides

CONTEXT

The bandgap of metal monochalcogenides (MMCs) is a key property that governs their physical and chemical properties. Accurate measurement of the bandgap is essential for a range of applications, including optoelectronics and photovoltaics. However, many theoretical approximations fail to accurately calculate the bandgap for MMCs, making it difficult to obtain precise values. This study investigated the suitability of the FP-LAPW/GAM-MPW1K scheme for determining the bandgap of MMCs. The investigation included lattice parameters, bandgap, band structure, and density of states, which were compared against both previous theoretical calculations and available experimental data. The findings of the study indicate that the FP-LAPW/GAM-MPW1K approach accurately calculates the bandgap value of MMCs by efficiently treating d-state electrons. The results are consistent with prior studies, confirming the method's reliability in determining the bandgap of these semiconductors.

METHODS

our study used the GAM-MPW1K functional and the full potential linearized augmented plane wave method (FP-LAPW) in the ELK code to calculate the lattice parameters, electronic band structure, and bandgap of ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe compounds in the wurtzite structure. The crystallographic data were obtained from the COD database and the inputs were prepared by CIF2CELL code. The results were visualized using Xmgrace and VESTA software.

Enhancing decomposition of rhodamine (RhB) and methylene blue (MB) using CdS decorated with Ag or Ru driven by visible radiation

The development of photocatalysts has an influential role in solving the environmental pollution crisis. Herein, the two different noble metals of silver (Ag)/ruthenium (Ru) were separately decorated on cadmium sulfide (CdS) photocatalysts by novel chemical methods. Characterization tests confirmed the formation of Ag/Ru-decorated CdS with spherical morphologies. According to the DRS and PL experiments, Ru-decorated CdS accounted for the highest light absorbance and the most accelerated transfer and detachment of photoelectrons/holes, followed by Ag-decorated CdS compared to pure CdS, which brought proper optical properties of Ag/Ru-decorated CdS. The photodecomposition of methylene blue (MB)/rhodamine B (RhB) as dyes and phenol as a colorless pollutant in the presence of Ag-decorated CdS (96%, 95%, and 69%) and Ru-decorated CdS (100%, 100%, and 80%) exposed to visible light radiation climbed compared to pure CdS (80%, 67%, and 61%) respectively. The influence of various parameters on the MB/RhB photocatalytic activity was investigated. The quenching experiment determined the functions of active species. Finally, experimental results proved that the MB/RhB photodecomposition by Ag/Ru-decorated CdS followed the pseudo-first-order kinetic model.

Controllable Fabrication of Zn2+ Self-Doped TiO2 Tubular Nanocomposite for Highly Efficient Water Treatment

Tailoring high-efficiency photocatalytic composites for various implementations is a major research topic. 1D TNTs-based nanomaterials show promise as a photocatalyst for the remediation of organic pigments in an aqueous solution. Despite this, TiO2 (TNTs) is only photoactive in the UV range due to its inherent restriction on absorption of light in the UV range. Herein, we provide a facile recipe to tailor the optical characteristics and photocatalytic activity of TNTs by incorporating Zn (II) ionic species via an ion-exchange approach in an aqueous solution. The inclusion of Zn (II) ions into the TNTs framework expands its absorption of light toward the visible light range, therefore TiO2 nanotubes shows the visible-light photo-performance. Activity performance on photocatalytic decontamination of RhB at ambient temperature demonstrates that Zn-TNTs offer considerable boosted catalytic performance compared with untreated tubular TiO2 during the illumination of visible light. RhB (10 mg L−1) degradation of around 95% was achieved at 120 min. Radical scavenger experiment demonstrated that when electron (e−) or holes (h+) scavengers are introduced to the photodegradation process, the assessment of decontamination efficacy decreased by 45% and 76%, respectively. This demonstrates a more efficient engagement of the photoexcited electrons over photogenerated holes in the photodegradation mechanism. Furthermore, there seems to be no significant decrease in the activity of the Zn-TNTs after five consecutive runs. As a result, the fabricated Zn-TNTs composite has a high economic potential in the energy and environmental domains.

Electronic Structure and Excited State Dynamics of Cadmium Chalcogenide Nanorods

The cylindrical quasi-one-dimensional shape of colloidal semiconductor nanorods (NRs) gives them unique electronic structure and optical properties. In addition to the band gap tunability common to nanocrystals, NRs have polarized light absorption and emission and high molar absorptivities. NR-shaped heterostructures feature control of electron and hole locations as well as light emission energy and efficiency. We comprehensively review the electronic structure and optical properties of Cd-chalcogenide NRs and NR heterostructures (e.g., CdSe/CdS dot-in-rods, CdSe/ZnS rod-in-rods), which have been widely investigated over the last two decades due in part to promising optoelectronic applications. We start by describing methods for synthesizing these colloidal NRs. We then detail the electronic structure of single-component and heterostructure NRs and follow with a discussion of light absorption and emission in these materials. Next, we describe the excited state dynamics of these NRs, including carrier cooling, carrier and exciton migration, radiative and nonradiative recombination, multiexciton generation and dynamics, and processes that involve trapped carriers. Finally, we describe charge transfer from photoexcited NRs and connect the dynamics of these processes with light-driven chemistry. We end with an outlook that highlights some of the outstanding questions about the excited state properties of Cd-chalcogenide NRs.

Review: Quantum Dot Light-Emitting Diodes

Quantum dot light-emitting diodes (QD-LEDs) are one of the most promising self-emissive displays in terms of light-emitting efficiency, wavelength tunability, and cost. Future applications using QD-LEDs can cover a range from a wide color gamut and large panel displays to augmented/virtual reality displays, wearable/flexible displays, automotive displays, and transparent displays, which demand extreme performance in terms of contrast ratio, viewing angle, response time, and power consumption. The efficiency and lifetime have been improved by tailoring the QD structures and optimizing the charge balance in charge transport layers, resulting in theoretical efficiency for unit devices. Currently, longevity and inkjet-printing fabrication of QD-LEDs are being tested for future commercialization. In this Review, we summarize significant progress in the development of QD-LEDs and describe their potential compared to other displays. Furthermore, the critical elements to determine the performance of QD-LEDs, such as emitters, hole/electron transport layers, and device structures, are discussed comprehensively, and the degradation mechanisms of the devices and the issues of the inkjet-printing process were also investigated.

Electric, magnetic, and shear field-directed assembly of inorganic nanoparticles

Ordered assemblies of inorganic nanoparticles (NPs) have shown tremendous potential for wide applications due to their unique collective properties, which differ from those of individual NPs. Various assembly methods, such as external field-directed assembly, interfacial assembly, template assembly, biomolecular recognition-mediated assembly, confined assembly, and others, have been employed to generate ordered inorganic NP assemblies with hierarchical structures. Among them, the external field-directed assembly method is particularly fascinating, as it can remotely assemble NPs into well-ordered superstructures. Moreover, external fields (e.g., electric, magnetic, and shear fields) can introduce a local and/or global field intensity gradient, resulting in an additional force on NPs to drive their rotation and/or translation. Therefore, the external field-directed assembly of NPs becomes a robust method to fabricate well-defined functional materials with the desired optical, electronic, and magnetic properties, which have various applications in catalysis, sensing, disease diagnosis, energy conversion/storage, photonics, nano-floating-gate memory, and others. In this review, the effects of an electric field, magnetic field, and shear field on the organization of inorganic NPs are highlighted. The methods for controlling the well-ordered organization of inorganic NPs at different scales and their advantages are reviewed. Finally, future challenges and perspectives in this field are discussed.

Raman Snapshots of Side-Chain Dependent Polaron Dynamics in PolyThiophene Films

Photogenerated polarons in π-conjugated polymers are the precursors to free charges at donor-acceptor interfaces. Unraveling the relationship between film morphology and polaron formation is conjectured to enable efficient charge generation in organic photovoltaic devices. However, it has been challenging to track the ultrafast dynamics of polarons selectively and thus evaluate the molecular coordinates that drive charge generation in films. Using a combination of broadband femtosecond transient absorption and resonance-selective femtosecond stimulated Raman spectroscopy, here, we investigate the polaron generation dynamics exclusively in traditional crystalline poly(3-hexylthiophene) (P3HT) and its amorphous side-chain variant poly(3-(2-ethylhexyl)thiophene-2,5-diyl) (P3EHT) films. The transient Raman data unequivocally provides evidence for an initial delocalization of the polaronic states via thiophene backbone planarization in ∼100 fs while capturing the subsequent morphology-dependent cooling dynamics in a few picoseconds. Our work highlights the structural significance of crystalline morphology in generating hot-charges and thereby emphasizes the importance of side-chain engineering in designing highly efficient conjugated polymer films for hot-carrier photovoltaic devices.

Three-Dimensional Nanopillar Arrays-Based Efficient and Flexible Perovskite Solar Cells with Enhanced Stability

Perovskite nanopillars (PNPs) are propitious candidates for solar irradiation harvesting and are potential alternatives to thin films in flexible photovoltaics. To realize efficient daily energy output, photovoltaics must absorb sunlight over a broad range of incident angles and wavelengths congruent with the solar spectrum. Herein, we report highly periodic three-dimensional (3D) PNP-based flexible photovoltaics possessing a core-shell structure. The vertically aligned PNP arrays demonstrate up to 95.70% and 75.10% absorption at peak and under an incident angle of 60°. The efficient absorption and the orthogonal carrier collection facilitate an external quantum efficiency of 84.0%-89.18% for broadband wavelength. PNPs have been successfully implemented in flexible solar cells. The porous alumina membrane protects PNPs against water and oxygen intrusion and thereby imparts robustness to photovoltaic devices. Meanwhile, the excellent tolerance to mechanical stress/strain enables our unique PNP-based device to provide efficient solar-to-electricity conversion while undergoing mechanical bending.

From Binary to Ternary Transition-Metal Nitrides: A Boost toward Nitrogen Magneto-Ionics

Magneto-ionics is an emerging actuation mechanism to control the magnetic properties of materials via voltage-driven ion motion. This effect largely relies on the strength and penetration of the induced electric field into the target material, the amount of generated ion transport pathways, and the ionic mobility inside the magnetic media. Optimizing all these factors in a simple way is a huge challenge, although highly desirable for technological applications. Here, we demonstrate that the introduction of suitable transition-metal elements to binary nitride compounds can drastically boost magneto-ionics. More specifically, we show that the attained magneto-ionic effects in CoN films (i.e., saturation magnetization, toggling speeds, and cyclability) can be drastically enhanced through 10% substitution of Co by Mn in the thin-film composition. Incorporation of Mn leads to transformation from nanocrystalline into amorphous-like structures, as well as from metallic to semiconducting behaviors, resulting in an increase of N-ion transport channels. Ab initio calculations reveal a lower energy barrier for CoMn-N compared to Co-N that provides a fundamental understanding of the crucial role of Mn addition in the voltage-driven magnetic effects. These results constitute an important step forward toward enhanced voltage control of magnetism via electric field-driven ion motion.

Plasmonic Enhanced SERS in Ag/TiO2 Nanostructured Film: An Experimental and Theoretical Study

In this work, we present a new study on the electromagnetic (EM) enhancement properties generated by Ag/TiO₂ toward the finger print of methylene blue (MB) molecules deposited on the surface of Ag nanostructures. SERS intensity generated by MB molecules reflects the interaction between the local electric field and their bonds. A power-dependent SERS study in order to reveal the magnitude effect of a local electric field on the vibration behavior of molecular bonds of MB was performed. A theoretical study using finite element (COMSOL Multiphysics) was performed in order to understand the effect of interparticle distance of Ag nanoparticles on the enhancement properties.

π-Orbital mediated charge transfer channels in a monolayer Gr-NiPc heterointerface unveiled by soft X-ray electron spectroscopies and DFT calculations

With the aim to identify charge transfer channels underlying device development and operation, X-Ray Photoelectron Spectroscopy (XPS), Near-Edge X-Ray Absorption Fine Structure (NEXAFS), and Resonant Photoelectron Spectroscopy (ResPES) have been employed to characterize a novel heterointerface obtained by the controlled evaporation of a Nickel Phthalocyanine (NiPc) monolayer on a single layer of Graphene (Gr) on SiC substrate. Indeed, the Gr-NiPc interface could be a promising candidate for different applications in the field of photonics, optoelectronics, and sensing, provided that clear information on the charge transfer mechanisms at the Gr-NiPc interface can be obtained. The analysis of the spectroscopic data has shown the effective functionalization and the horizontally-flat disposition of the NiPc complexes over the Gr layer. With this geometry, the main intermolecular interaction experienced by the NiPc species is the coupling with the Gr substrate, through π-symmetry orbitals, as revealed by the different behaviour of the valence band photoemission at resonance with the N K-edge and Ni L₃-edge. These results have been supported by the analysis of density functional theory (DFT) calculations, that allowed for a rationalization of the experimental data, showing that charge transfer at the interface occurs from the doubly degenerate e_g LUMO orbital, involving mainly N and C (pyrrole ring) p_z states, to the holes in the p-doped graphene layer.

Force-driven active dynamics of thin nanorods in unentangled polymer melts

Recent advances in the functional material and biomedical applications of nanorods call for a fundamental understanding of the active motion of nanorods in a viscoelastic medium. Molecular dynamics simulations are performed to investigate a model system consisting of force-driven active thin nanorods in a melt of unentangled polymers. The activeness of a thin nanorod arises from a constant external force applied uniformly along the rod. The simulations demonstrate that the active force overcomes the randomness of the diffusive motion and results in a ballistic motion along the direction of the applied force at long timescales. The constant speed of the force-driven ballistic motion is determined by the balance of the active force and the friction from the coupling of the nanorod with the polymer viscosity. The friction coefficient, which is computed as the ratio of the active force and the speed, decreases as the active force increases. The origin of the reduction in the friction coefficient is the high speed that allows the nanorod to renew its local environment faster than the relaxation time of melt chains. A scaling theory is developed to quantify the dependence of the friction coefficient on the strength of the active force. The simulations also demonstrate that the force-driven ballistic motion suppresses the rotational diffusion of the rod and cuts off the de-correlation of the rod axis with time. On the scaling level, the long-time trajectory of a force-driven active nanorod piercing through unentangled polymers may be described as a stretched array of "active blobs", where the short-time random-walk trajectory within an active blob is unperturbed by the active force.

Conjugated Block Copolymers for Functional Nanostructures

Conjugated polymers have been actively studied as an alternative to inorganic semiconductors for their unique optical and electrical properties and low-cost solution processability. However, typical conjugated polymer films contain numerous defects that negatively affect their transport properties, which remains a major issue despite much effort to develop ways to improve the molecular packing structure. In principle, conjugated block copolymers (BCPs) composed of a rod-type conjugated polymer and a coil-type insulating polymer can assemble into various types of ordered nanostructures based on the microphase segregation of two polymer blocks. However, such assembly typically requires a relatively large volume fraction of the coil block or modification of the rod block, both of which tend to impede charge transport. As an alternative, we and others have fabricated nanoscale assemblies of conjugated BCPs via solution-phase self-assembly, which can be used as building blocks for construction of extended nanoarrays of conjugated polymers. In particular, BCPs containing poly(3-hexylthiophene) (P3HT), a conjugated polymer widely used for its high hole mobility, form highly ordered and technologically relevant one-dimensional (1D) nanowires with controlled lengths. A range of well-defined assembly structures such as square plates, ribbons, vesicles, and helices have been prepared from various conjugated BCPs, resembling those of peptide self-assembly, forming diverse nanostructures through combinations of π-π stacking, hydrogen bonding, and hydrophobic interactions.When the self-assembly of P3HT BCPs takes place at an air-water interface, the initially formed polymer nanowires further assemble into hierarchical two-dimensional (2D) nanoarrays with solvent evaporation. The fluidic nature of the water subphase allows fabrication of highly ordered assembly structures from P3HT BCPs with high P3HT content. The ultrathin free-standing film integrated in a field effect transistor (FET) showed orders of magnitude higher current and hole mobility compared to that fabricated by conventional spin-coating. Furthermore, binary self-assembly of a P3HT BCP and quantum dots (QDs) at the air-water interface generates well-ordered 2D films of alternating P3HT nanowires and 1D QD arrays. Unlike coil-coil BCP systems, QDs reside at the interface between P3HT and coil blocks for a broad range of QD sizes due to the strong P3HT packing interactions and the flexible water subphase, forming tight p-n junctions for enhanced photocurrent. Incorporation of magnetic nanoparticles can further improve the degree of order, enabling fabrication of long-range order and direction-controlled P3HT nanoarrays through magnetic-field induced self-assembly.The conjugated BCP approach is highly modular and can be combined with various types of functional molecules, polymers, and nanoparticles, offering a powerful platform for fabrication of functional polymer nanostructures with desired morphologies and properties. This Account introduces recent advances in the self-assembly of π-conjugated BCPs, describes how they differ from prototypical coil-coil type BCPs, and discusses current issues and future outlooks.

Synthesis, X-ray structure, antimicrobial activity, DFT and molecular docking studies of N-(thiophen-2-ylmethyl)thiophene-2-carboxamide

In the present study, N-(thiophen-2-ylmethyl)thiophene-2-carboxamide, C10H9NOS2, (I), was obtained by the reaction of thiophene-2-carbonyl chloride and thiophen-2-ylmethanamine. Characterization of (I) was carried out using X-ray diffraction, spectroscopic techniques and elemental analyses. The DFT/B3LYP/6-311++G(d,p) theoretical level was successfully applied to calculate the optimized geometry and the local and global chemical activity parameters. The results obtained show good agreement between the experimental and theoretical geometrical parameters. The local and global chemical activity parameters were examined to determine the electrophilic and nucleophilic sites in (I). The natural bond orbital (NBO) analysis of (I) gives an efficient methodology for investigating the inter- and intramolecular bonding, as well as giving a convenient basis for investigating charge transfer or conjugative interactions in molecular systems. Also, the antimicrobial activity of (I) was investigated against eight microorganisms using the microdilution method and it is found to have an effective antibacterial activity. In addition, molecular docking studies were calculated in order to understand the nature of the binding of (I) with a lung cancer protein (PDB entry 1x2j).

The superior effect of edge functionalization relative to basal plane functionalization of graphene in enhancing the thermal conductivity of polymer-graphene nanocomposites - a combined molecular dynamics and Green's functions study

To achieve polymer-graphene nanocomposites with high thermal conductivity (k), it is critically important to achieve efficient thermal coupling between graphene and the surrounding polymer matrix through effective functionalization schemes. In this work, we demonstrate that edge-functionalization of graphene nanoplatelets (GnPs) can enable a larger enhancement of effective thermal conductivity in polymer-graphene nanocomposites relative to basal plane functionalization. Effective thermal conductivity for the edge case is predicted, through molecular dynamics simulations, to be up to 48% higher relative to basal plane bonding for 35 wt% graphene loading with 10 layer thick nanoplatelets. The beneficial effect of edge bonding is related to the anisotropy of thermal transport in graphene, involving very high in-plane thermal conductivity (∼2000 W m^-1 K^-1) compared to the low out-of-plane thermal conductivity (∼10 W m^-1 K^-1). Likewise, in multilayer graphene nanoplatelets (GnPs), the thermal conductivity across the layers is even lower due to the weak van der Waals bonding between each pair of layers. Edge functionalization couples the polymer chains to the high in-plane thermal conduction pathway of graphene, thus leading to overall high thermal conductivity of the composite. Basal-plane functionalization, however, lowers the thermal resistance between the polymer and the surface graphene sheets of the nanoplatelet only, causing the heat conduction through inner layers to be less efficient, thus resulting in the basal plane scheme to be outperformed by the edge scheme. The present study enables fundamentally novel pathways for achieving high thermal conductivity polymer nanocomposites.

Single-Crystalline Pyramidal TiCx Particles Grown by Biphase Diffusion Synthesis

In this study, we present single-crystalline pyramid-shaped (SP) TiC_x particles synthesized on a stacked melt (copper)-solid (titanium) substrate using a biphase diffusion synthesis (BDS) method, in which different sizes ranging from nano- to micrometer scale were obtained within the copper melt with the {100} planes exposed to air. Direct observation and further plasma treatment of the pyramids at different self-assembly stages facilitated the investigation of their growth mode, especially in the horizontal plane. The dendritic growth mode along with the edge and corner-shared modes of the SP TiC_x particles frozen on the copper surface was investigated. With SP TiC_x particles stacked on top, MoS₂-based phototransistors exhibited an up to 6-fold photocurrent increase under laser illumination at different wavelengths, which was attributed to the localized surface plasmonic resonance (LSPR) effect. The BDS method is applied for the synthesis of SP TiC_x particles, with a detailed investigation of the relevant growth mode and related applications, such as decoration for high-performance photodevices.

Colloidal Bismuth Chalcohalide Nanocrystals

Here we present a colloidal approach to synthesize bismuth chalcohalide nanocrystals (BiEX NCs, in which E=S, Se and X=Cl, Br, I). Our method yields orthorhombic elongated BiEX NCs, with BiSCl crystallizing in a previously unknown polymorph. The BiEX NCs display a composition‐dependent band gap spanning the visible spectral range and absorption coefficients exceeding 10⁵ cm⁻¹. The BiEX NCs show chemical stability at standard laboratory conditions and form colloidal inks in different solvents. These features enable the solution processing of the NCs into robust solid films yielding stable photoelectrochemical current densities under solar‐simulated irradiation. Overall, our versatile synthetic protocol may prove valuable in accessing colloidal metal chalcohalide nanomaterials at large and contributes to establish metal chalcohalides as a promising complement to metal chalcogenides and halides for applied nanotechnology.

Nanoparticle anisotropy induces sphere-to-cylinder phase transition in block copolymer melts

Block copolymer nanocomposites including anisotropic nanoparticles have been previously found to co-assemble into complex structures with nanoparticle alignment. Anisotropic nanoparticles with large aspect ratios are found to modify the morphology of block copolymers at modest concentrations, inducing a sphere-to-cylinder phase transition by breaking the local symmetry in the vicinity of a solid particle. This transition takes place over a wide range of NP lengths comparable with the BCP spacing. Controlling the orientation of uniaxial nanoparticles provides additional control over the global orientation of the block copolymer, as previously reported by experiments.

Hybrid Time-Dependent Ginzburg–Landau Simulations of Block Copolymer Nanocomposites: Nanoparticle Anisotropy

Block copolymer melts are perfect candidates to template the position of colloidal nanoparticles in the nanoscale, on top of their well-known suitability for lithography applications. This is due to their ability to self-assemble into periodic ordered structures, in which nanoparticles can segregate depending on the polymer–particle interactions, size and shape. The resulting coassembled structure can be highly ordered as a combination of both the polymeric and colloidal properties. The time-dependent Ginzburg–Landau model for the block copolymer was combined with Brownian dynamics for nanoparticles, resulting in an efficient mesoscopic model to study the complex behaviour of block copolymer nanocomposites. This review covers recent developments of the time-dependent Ginzburg–Landau/Brownian dynamics scheme. This includes efforts to parallelise the numerical scheme and applications of the model. The validity of the model is studied by comparing simulation and experimental results for isotropic nanoparticles. Extensions to simulate nonspherical and inhomogeneous nanoparticles are discussed and simulation results are discussed. The time-dependent Ginzburg–Landau/Brownian dynamics scheme is shown to be a flexible method which can account for the relatively large system sizes required to study block copolymer nanocomposite systems, while being easily extensible to simulate nonspherical nanoparticles.

Chemically Edge-Carboxylated Graphene Enhances the Thermal Conductivity of Polyetherimide-Graphene Nanocomposites

In this work, we demonstrate that edge oxidation of graphene can enable larger enhancement in thermal conductivity (k) of graphene nanoplatelet (GnP)/polyetherimide (PEI) composites relative to oxidation of the basal plane of graphene. Edge oxidation offers the advantage of leaving the basal plane of graphene intact, preserving its high in-plane thermal conductivity (k_in > 2000 W m^-1 K^-1), while, simultaneously, the oxygen groups introduced on the graphene edge enhance interfacial thermal conductance through hydrogen bonding with oxygen groups of PEI, enhancing the overall polymer composite thermal conductivity. Edge oxidation is achieved in this work by oxidizing graphene in the presence of sodium chlorate and hydrogen peroxide, thereby introducing an excess of carboxyl groups on the edge of graphene. Basal plane oxidation of graphene, on the other hand, is achieved through the Hummers method, which distorts the sp² carbon-carbon network of graphene, dramatically lowering its intrinsic thermal conductivity, causing the BGO/PEI (BGO = basal-plane oxidized graphene or basal-plane-functionalized graphene oxide) composite's k value to be even lower than pristine GnP/PEI composite's k value. The resulting thermal conductivity of the EGO/PEI (EGO = edge-oxidized graphene or edge-functionalized graphene oxide) composite is found to be enhanced by 18%, whereas that of the BGO/PEI composite is diminished by 57%, with respect to the pristine GnP/PEI composite with 10 wt % GnP content. Two-dimensional Raman mapping of GnPs is used to confirm and distinguish the location of oxygen functional groups on graphene. The superior effect of edge bonding presented in this work can lead to fundamentally novel pathways for achieving high thermal conductivity polymer composites.

Study of the Chain Condensation Process from a Dilute to a Concentrated Solution and the Transformation of the Chain Conformation from a Solution to a Film for the Conjugated Polymer PFO

The chain behavior in a precursor solution and its condensation process are still key issues that have been paid close attention to but have not been solved yet for semirigid conjugated polymers. In this research, the chain condensation process from a dilute to a concentrated solution and the transformation of the chain conformation from a solution to a film for the conjugated polymer poly(9,9'-dioctylfluorene) (PFO) were investigated by a scaling law method obtained from rheological measurements. By establishing a scaling relationship between specific viscosity and concentration, it was found that the motion of molecular chains conformed to the Zimm model in dilute solution, and the motion of molecular chains conformed to the Rouse model in semidilute unentangled solution as well as conformed to the Edwards tube model in semidilute entangled solution. Furthermore, it was also found that toluene is a θ solvent for PFO at 25 °C. Some important physical parameters in connection with PFO intrinsic properties were also obtained here, such as intrinsic viscosity [η] = 136.84 mL g^-1, root-mean-square end-to-end distance R = 41.4 nm, and Kuhn segment length b = 6.28 nm. In particular, this was the first time that the effect of the film-forming process of spin coating on the transformation proces of the PFO chain conformation from the precursor solution to a film was studied, and the spin-coating time (t) was found to be several orders of magnitude longer than the PFO chain relaxation time (τ _Z(τ _R)). This research enriches knowledge and understanding of the chain behavior in the precursor solution for semirigid conjugated polymers and reveals the correlation of chain behaviors in solution with the film's condensed state structure in the process of chain dynamic evolution from a solution to a film.

A study on structural, optical, and electrical characteristics of perovskite CsPbBr3 QD/2D-TiSe2 nanosheet based nanocomposites for optoelectronic applications

Lead halide perovskite (CsPbBr₃) quantum dots (QDs) and two-dimensional (2D) layered transition metal dichalcogenides have a significant application in solution-processed optoelectronic devices. Here, we report the oleylamine-assisted exfoliation of TiSe₂ nanosheets (NSs) in dichlorobenzene with high concentration and stable dispersion. The functionalized TiSe₂ NSs were used to synthesize the solution-processed perovskite CsPbBr₃ QD/TiSe₂ NS-based nanocomposite. The perovskite QDs and TiSe₂ NSs were characterized by different techniques. The strong photoluminescence (PL) quenching and decreased lifetime decay of the nanocomposite indicates efficient charge transfer from photo-excited CsPbBr₃ to TiSe₂ NSs. The calculated charge-transfer rate constant (K_ET) from photo-excited CsPbBr₃ to TiSe₂ NSs increased from 1.50 × 10⁸ to 2.79 × 10⁸ s^-1 in different concentrations of TiSe₂ NSs (5 to 20 μg mL^-1), respectively. Furthermore, the photo-currents of CsPbBr₃ QD/TiSe₂ NS nanocomposite devices were dramatically enhanced ∼2 times compared to pristine CsPbBr₃ QD based devices, which supports the charge transfer and charge separation in nanocomposite devices.

Vacuum-Free Quantum Dots Planar Hybrid Solar Cells: Improving Charge Transport Using Reduced Graphene Oxide and PEO as the Buffer Layer

In this work, reduced graphene oxide (rGO) was synthesized using a modified Hummer method and its morphological and structural properties were investigated using transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) and X-ray diffraction (XRD). The rGO was used as the hole transport buffer layer (HTBL) and poly(ethylene oxide) (PEO) was used as the electron transport buffer layer (ETBL) for the vacuum-free quantum dot planar hybrid (VFQPH) solar cells (SCs) fabrication. PbS quantum dots (Qdots) were prepared using a hot-injection method, which was used as the p-type material and PCBM ([6,6]-Phenyl-C61-butyric acid methyl ester) was used as the n-type material. The effects of the hole transport buffer layer and electron transport buffer layer on the morphological and electrical properties of the device were investigated. A device with a structure of glass/indium tin oxide (ITO)/HTBL/PbS: PCBM/ETBL/E-GaIn was fabricated and the maximum power conversion efficiency of about 4.34% was obtained.

Donor–acceptor organic nanostructure based on conjugated polymer for improving visible-light-driven photocatalytic activity towards degradation of dye in aqueous medium

Hybrid donor–acceptor nanostructures based on P3HT with improved light harvesting properties were employed for organic dye degradation.

Recent advances in the synthesis of cyclic compounds using α,α-dicyanoolefins as versatile vinylogous nucleophiles

This article provides a review of the applications of α,α-dicyanoolefins as versatile vinylogous nucleophiles in the synthesis of various cyclic compounds, covering the literature from the past 13 years.

Bright and Stable Quantum Dot Light-Emitting Diodes

Quantum dot light-emitting diodes (QLEDs) are one of the most promising candidates for next-generation displays and lighting sources, but they are barely used because vulnerability to electrical and thermal stresses precludes high brightness, efficiency, and stability at high current density (J) regimes. Here, bright and stable QLEDs on a Si substrate are demonstrated, expanding their potential application boundary over the present art. First, a tailored interface is granted to the quantum dots, maximizing the quantum yield and mitigating nonradiative Auger decay of the multiexcitons generated at high-J regimes. Second, a heat-endurable, top-emission device architecture is employed and optimized based on optical simulation to enhance the light outcoupling efficiency. The multilateral approaches realize that the red top-emitting QLEDs exhibit a maximum luminance of 3 300 000 cd m^-2 , a current efficiency of 75.6 cd A^-1 , and an operational lifetime of 125 000 000 h at an initial brightness of 100 cd m^-2 , which are the highest of the values reported so far.

Shell thickness dependent photostability studies of green-emitting "Giant" quantum dots

Highly efficient green-emitting core/shell giant quantum dots have been synthesized through a facile "one-pot" gradient alloy approach. Furthermore, an additional ZnS shell was grown using the "Successive Ionic Layer Adsorption and Reaction" (SILAR) method. Due to the faster reactivity of Cd and Se compared to an analogue of Zn and S precursors it is presumed that CdSe nuclei are initially formed as the core and gradient alloy shells simultaneously encapsulate the core in an energy-gradient manner and eventually thick ZnS shells were formed. Using this gradient alloy approach, we have synthesized four different sized green-emitting giant core-shell quantum dots to study their shell thickness-dependent photostability under continuous UV irradiation, and temperature-dependent PL properties of nanocrystals. There was a minimum effect of the UV light exposure on the photostability beyond a certain thickness of the shell. The QDs with a diameter of ≥8.5 nm show substantial improvement in photostability compared to QDs with a diameter ≤ 7.12 nm when continuously irradiated under strong UV light (8 W cm^-2, 365 nm) for 48 h. The effect of temperature on the photoluminescence intensities was studied with respect to the shell thickness. There were no apparent changes in PL intensities observed for the QDs ≥ 8.5 nm, on the contrary, for example, QDs with <8.5 nm in diameter (for ∼7.12 nm) show a decrease in PL intensity at higher temperatures ∼ 90 °C. The synthesized green-emitting gradient alloy QDs with superior optical properties can be used for highly efficient green-emitters and are potentially applicable for the fabrication of green LEDs.

Solution-processed two-dimensional materials for next-generation photovoltaics

In the ever-increasing energy demand scenario, the development of novel photovoltaic (PV) technologies is considered to be one of the key solutions to fulfil the energy request. In this context, graphene and related two-dimensional (2D) materials (GRMs), including nonlayered 2D materials and 2D perovskites, as well as their hybrid systems, are emerging as promising candidates to drive innovation in PV technologies. The mechanical, thermal, and optoelectronic properties of GRMs can be exploited in different active components of solar cells to design next-generation devices. These components include front (transparent) and back conductive electrodes, charge transporting layers, and interconnecting/recombination layers, as well as photoactive layers. The production and processing of GRMs in the liquid phase, coupled with the ability to "on-demand" tune their optoelectronic properties exploiting wet-chemical functionalization, enable their effective integration in advanced PV devices through scalable, reliable, and inexpensive printing/coating processes. Herein, we review the progresses in the use of solution-processed 2D materials in organic solar cells, dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic-inorganic hybrid solar cells, as well as in tandem systems. We first provide a brief introduction on the properties of 2D materials and their production methods by solution-processing routes. Then, we discuss the functionality of 2D materials for electrodes, photoactive layer components/additives, charge transporting layers, and interconnecting layers through figures of merit, which allow the performance of solar cells to be determined and compared with the state-of-the-art values. We finally outline the roadmap for the further exploitation of solution-processed 2D materials to boost the performance of PV devices.

Ordered nanostructures arrays fabricated by anodic aluminum oxide (AAO) template-directed methods for energy conversion

Clean and efficient energy conversion systems can overcome the depletion of the fossil fuel and meet the increasing demand of the energy. Ordered nanostructures arrays convert energy more efficiently than their disordered counterparts, by virtue of their structural merits. Among various fabrication methods of these ordered nanostructures arrays, anodic aluminum oxide (AAO) template-directed fabrication have drawn increasing attention due to its low cost, high throughput, flexibility and high structural controllability. This article reviews the application of ordered nanostructures arrays fabricated by AAO template-directed methods in mechanical energy, solar energy, electrical energy and chemical energy conversions in four sections. In each section, the corresponding advantages of these ordered nanostructures arrays in the energy conversion system are analysed, and the limitation of the to-date research is evaluated. Finally, the future directions of the ordered nanostructures arrays fabricated by AAO template-directed methods (the promising method to explore new growth mechanisms of AAO, green fabrication based on reusable AAO templates, new potential energy conversion application) are discussed.

Plasmon-Enhanced Light Absorption in (p-i-n) Junction GaAs Nanowire Solar Cells: An FDTD Simulation Method Study

A finite-difference time-domain method is developed for studying the plasmon enhancement of light absorption from vertically aligned GaAs nanowire arrays decorated with Au nanoparticles. Vertically aligned GaAs nanowires with a length of 1 µm, a diameter of 100 nm and a periodicity of 165-500 nm are functionalized with Au nanoparticles with a diameter between 30 and 60 nm decorated in the sidewall of the nanowires. The results show that the metal nanoparticles can improve the absorption efficiency through their plasmonic resonances, most significantly within the near-bandgap edge of GaAs. By optimizing the nanoparticle parameters, an absorption enhancement of almost 35% at 800 nm wavelength is achieved. The latter increases the chance of generating more electron-hole pairs, which leads to an increase in the overall efficiency of the solar cell. The proposed structure emerges as a promising material combination for high-efficiency solar cells.

Tuning Hierarchical Order and Plasmonic Coupling of Large-Area, Polymer-Grafted Gold Nanorod Assemblies via Flow-Coating

Solution-based printing of anisotropic nanostructures is foundational to many emerging technologies, such as energy storage devices, photonic elements, and sensors. Methods to rapidly (>mm/s) manufacture large area assemblies (≫cm²) with simultaneous control of thickness (<10 nm), nanoparticle spacing (<5 nm), surface roughness (<5 nm), and global and local orientational order are still lacking. Herein, we demonstrate such capability using flow-coating to fabricate robust, self-supporting mono- and bilayer films of polystyrene-grafted gold nanorods (PS-AuNRs) onto solid substrates. The relationship among solvent evaporation, deposition speed, substrate surface energy, concentration, and film thickness for solutions of such hairy hybrid nanoparticles spans the Landau-Levich and evaporative film formation regimes. In the Landau-Levich regime, solvent evaporation rapidly concentrates the PS-AuNRs, leading to the formation of thin films with distinct, randomized side-by-side domains. Alternatively, processing at slower velocities in the evaporative regime results in the global alignment of PS-AuNRs. Processing speed and substrate surface energy afford tuning of the film's optical extinction of a given PS-AuNR via fine control of inter-rod distance and subsequent plasmonic coupling between neighboring nanorods. Because the concept of the polymer-grafted nanorod can be expanded to a variety of different polymer canopies, shapes, and core materials, the processing-structure relationships established in this work will have important implications on the future development of anisotropic nanostructure-based applications.

Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77Se and 113Cd Solid-State NMR Spectroscopy

Dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) spectroscopy was used to obtain detailed surface structures of zinc blende CdSe nanocrystals (NCs) with plate or spheroidal morphologies which are capped by carboxylic acid ligands. 1D ¹¹³Cd and ⁷⁷Se cross-polarization magic angle spinning (CPMAS) NMR spectra revealed distinct signals from Cd and Se atoms on the surface of the NCs, and those residing in bulk-like environments, below the surface. ¹¹³Cd cross-polarization magic-angle-turning (CP-MAT) experiments identified CdSe₃O, CdSe₂O₂, and CdSeO₃ Cd coordination environments on the surface of the NCs, where the oxygen atoms are presumably from coordinated carboxylate ligands. The sensitivity gain from DNP enabled natural isotopic abundance 2D homonuclear ¹¹³Cd-¹¹³Cd and ⁷⁷Se-⁷⁷Se and heteronuclear ¹¹³Cd-⁷⁷Se scalar correlation solid-state NMR experiments which revealed the connectivity of the Cd and Se atoms. Importantly, ⁷⁷Se{¹¹³Cd} scalar heteronuclear multiple quantum coherence (J-HMQC) experiments were used to selectively measure one-bond ⁷⁷Se-¹¹³Cd scalar coupling constants (¹J(⁷⁷Se, ¹¹³Cd)). With knowledge of ¹J(⁷⁷Se, ¹¹³Cd), heteronuclear ⁷⁷Se{¹¹³Cd} spin echo (J-resolved) NMR experiments were used to determine the number of Cd atoms bonded to Se atoms and vice versa. The J-resolved experiments directly confirmed that major Cd and Se surface species have CdSe₂O₂ and SeCd₄ stoichiometries, respectively. Considering the crystal structure of zinc blende CdSe and the similarity of the solid-state NMR data for the platelets and spheroids, we conclude that the surface of the spheroidal CdSe NCs is primarily composed of {100} facets. The methods outlined here will generally be applicable to obtain detailed surface structures of various main group semiconductor nanoparticles.

Inorganic-Ligand Quantum Dots Meet Inorganic-Ligand Semiconductor Nanoplatelets: A Promising Fusion to Construct All-Inorganic Assembly

By the reaction of inorganic-ligand CdS/Cd²⁺ quantum dots (QDs) with inorganic-ligand CdSe/CdS/S^2- nanoplatelets (NPLs), semiconductor CdS QDs were fused with CdSe/CdS NPLs to yield all-inorganic assemblies, accompanied by great photoluminescence-enhancement. These all-inorganic assemblies facilitate charge transport between each other and open up interesting prospects with electronic and optoelectronic nanodevices.