Functionalized self-assembly of colloidal CdX (X = S, Se) nanorods on solid substrates for device applications

Recent advances in integrated solar cell/supercapacitor devices: Fabrication, strategy and perspectives

BACKGROUND

Solar cell/supercapacitor integrated devices (SCSD) have made some progress in terms of device structure and electrode materials, but there are still many key challenges in controlling electrode performance and improving the efficiency of integrated devices.

AIM OF REVIEW

It is necessary to study how to balance the photoelectric conversion process and the storage process. From the microscopic mechanism of different functional unit materials to the mechanism of macroscopic devices, it is essential to conduct in-depth research.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Here, the structures and preparation methods of various types of integrated SCSD were introduced. Then, the strategies for improving the overall performance of integrated devices were evaluated. Finally, the key objectives of reducing the cost of materials, increasing the stability and sustainability of devices were highlighted. Better matching of different functional units of devices was also prospected.

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.

Swelling, collapse and ordering of rod-like microgels in solution: Computer simulation studies

Polymer microgels have proven to be highly promising macromolecular objects for a wide variety of applications. In particular, the soft particles of an anisotropic (rod-like) shape are of special interest because of their potential use in tissue engineering or materials design. However, a little is known about the physical behavior of such microgels in solution, which inspired us to study them using mesoscopic computer simulations. For single networks, depending on the solvent quality, the dimensional characteristics were obtained for microgels of different molecular weight, crosslinking density and aspect ratio. In particular, the conditions for the rod-to-rod (preserving the nonspherical shape) and rod-to-sphere collapse were found. In addition, the effect of the liquid-crystalline (LC) ordering was demonstrated for the ensemble of rod-like microgels at different swelling ratios, and the influence of microgel aspect ratio on the volume fraction of the LC transition was shown.

Covalently Linked, Two-Dimensional Quantum Dot Assemblies

Using nanoscale building blocks to construct hierarchical materials is a radical new branch point in materials discovery that promises new structures and emergent functionality. Understanding the design principles that govern nanoparticle assembly is critical to moving this field forward. By exploiting mixed ligand environments to target patchy nanoparticle surfaces, we have demonstrated a novel method of colloidal quantum dot (QD) assembly that gives rise to 2D structures. The equilibration of solutions of spherical and quasispherical QDs, including CdS, CdSe, and InP, with 2,2'-bipyridine-5,5'-diacrylic acid resulted in the preferential formation of 2D assemblies over the course of days as determined by transmission electron microscopy analysis. Small-angle X-ray scattering confirms the existence of the QD assemblies in solution. The dependence of the assembly on linker properties (length and rigidity), linker concentration, and total concentration was investigated, together with the data point to a mechanism involving ligand redistribution to create a patchy surface that maximizes the steric repulsion of neighboring QDs. By operating in an underexchanged regime, the arising patchiness results in enthalpically preferred directions of cross-linking that can be accessed by thermal equilibration.

Light trapping structures and plasmons synergistically enhance the photovoltaic performance of full-spectrum solar cells

A full-spectrum solar cell exhibits potential as an effective strategy to enhance the absorption of incident solar light. To ensure the absorption capability of solar cells, trapping structures or plasmons have emerged as two main ways of utilizing the full spectrum of solar energy. First, recent progress in the full-spectrum solar cells based on NCs was reviewed from the aspects of trapping structures and plasmon design. Moreover, the effects of light trapping and surface plasmon resonance on light absorption and photoelectronic conversion were emphasized and discussed. Finally, the application prospect of their combination in the field of full-spectrum solar cells was examined. It was pointed out that the deep exploration of the physical mechanism of photoelectric conversion, controllable preparation of the interface and stability of composite structures will become the main directions of future research.

Excitonic phenomena in perovskite quantum-dot supercrystals

Quantum confinement and collective excitations in perovskite quantum-dot (QD) supercrystals offer multiple benefits to the light emitting and solar energy harvesting devices of modern photovoltaics. Recent advances in the fabrication technology of low dimensional perovskites has made the production of such supercrystals a reality and created a high demand for the modelling of excitonic phenomena inside them. Here we present a rigorous theory of Frenkel excitons in lead halide perovskite QD supercrystals with a square Bravais lattice. The theory shows that such supercrystals support three bright exciton modes whose dispersion and polarization properties are controlled by the symmetry of the perovskite lattice and the orientations of QDs. The effective masses of excitons are found to scale with the ratio of the superlattice period and the number of QDs along the supercrystal edge, allowing one to fine-tune the electro-optical response of the supercrystals as desired for applications. We also calculate the conductivity of perovskite QD supercrystals and analyze how it is affected by the optical generation of the three types of excitons. This paper provides a solid theoretical basis for the modelling of two- and three-dimensional supercrystals made of perovskite QDs and the engineering of photovoltaic devices with superior optoelectronic properties.

3D superstructures with an orthorhombic lattice assembled by colloidal PbS quantum dots

We report a new type of metamaterial comprising a highly ordered 3D network of 3-7 nm lead sulfide quantum dots self-assembled in an organic matrix formed by amphiphilic ligands (oleic acid molecules). The obtained 3D superstructures possess an orthorhombic lattice with the distance between the nanocrystals as large as 10-40 nm. Analysis of self-assembly and destruction of the superstructures in time performed by a SAXS technique shows that their morphology depends on the quantity of amphiphilic ligands and width of the quantum dot size and its distribution. Formation of the superstructures is discussed in terms of a model describing the lyotropic crystal formation by micelles from three-phase mixtures. The results show that the organic molecules possessing surfactant properties and capable of forming micelles with nanoparticles as a micelle core can be utilized as building blocks for the creation of novel metamaterials based on a highly ordered 3D network of semiconductors, metals or magnetic nanoparticles.

Synergy of polypyrrole and carbon x-aerogel in lithium-oxygen batteries

A crucial step in the development of lithium-oxygen (Li-O₂) batteries is to design an oxygen cathode with high catalytic activity and stable porous structure. Achieving such design requires an integrated strategy in which porosity, conductivity, catalytic activity, and mechanical durability are all considered in a battery system. Here, we develop polypyrrole-coated carbon x-aerogels with macroscopic 3D architecture, and demonstrate their potential as oxygen cathodes for Li-O₂ batteries. This material, a novel and mechanically strong composite aerogel with polymer-cross-linked structure, not only provides effective pores that allow to store the discharge products and open channels for better oxygen diffusion, but also forms a robust 3D catalytic network that promotes both oxygen reduction and evolution reactions with improved mechanical and electrochemical stability. This work highlights the synergy between the 3D porous, conductive carbon aerogel framework and the polypyrrole catalytic layer, which maintains stable catalytic activity without deactivation and provides a more effective gas-liquid-solid interface for rapid oxygen absorption and diffusion, thereby leading to significant improvements in the capacity, rate capability and cycle life of the cathode.