Seeded semiconductor nanorods represent a unique family of quantum confined materials that manifest characteristics of mixed dimensionality. They show polarized emission with high quantum yield and fluorescence switching under an electric field, features that are desirable for use in display technologies and other optical applications. So far, their robust synthesis has been limited mainly to CdSe/CdS heterostructures, thereby constraining the spectral tunability to the red region of the visible spectrum. Herein we present a novel synthesis of CdSe/CdZnS seeded nanorods with a radially graded composition that show bright and highly polarized green emission with minimal intermittency, as confirmed by ensemble and single nanorods optical measurements. Atomistic pseudopotential simulations elucidate the importance of the Zn atoms within the nanorod structure, in particular the effect of the graded composition. Thus, the controlled addition of Zn influences and improves the nanorods' optoelectronic performance by providing an additional handle to manipulate the degree confinement beyond the common size control approach. These nanorods may be utilized in applications that require the generation of a full, rich spectrum such as energy-efficient displays and lighting.
The chemical compositions and structures of organic-inorganic interfaces in mesostructurally ordered conjugated polymer-titania nanocomposites are shown to have a predominant influence on their photovoltaic properties. Such interfaces can be controlled by using surfactant structure-directing agents (SDAs) with different architectures and molecular weights to promote contact between the highly hydrophobic electron-donating conjugated polymer species and hydrophilic electron-accepting titania frameworks. A combination of small-angle X-ray scattering (SAXS), scanning and transmission electron microscopy (SEM, TEM), and solid-state NMR spectroscopy yields insights on the compositions, structures, and distributions of inorganic and organic species within the materials over multiple length scales. Two-dimensional NMR analyses establish the molecular-level interactions between the different SDA blocks, the conjugated polymer, and the titania framework, which are correlated with steady-state and time-resolved photoluminescence measurements of the photoexcitation dynamics of the conjugated polymer and macroscopic photocurrent generation in photovoltaic devices. Molecular understanding of the compositions and chemical interactions at organic-inorganic interfaces are shown to enable the design, synthesis, and control of the photovoltaic properties of hybrid functional materials.
Colloidal InP-based quantum dots are a promising material for light-emitting applications as an environment friendly alternative to their Cd-containing counterparts. Especially for their use in optoelectronic devices, it is essential to understand how charge carriers relax to the emitting state after injection with excess energy and if all of them arrive at this desired state. Herein, we report time-resolved differential transmission measurements on colloidal InP/ZnS and InP/ZnSe core/shell quantum dots. By optically exciting and probing individual transitions, we are able to distinguish between electron and hole relaxation. This, in turn, allows us to determine how the initial excess energy of the charge carriers affects the relaxation processes. According to the electronic level scheme, one expects a strong phonon bottleneck for electrons, whereas holes should relax easier as their energy levels are more closely spaced. On the contrary, we find that electrons relax faster than holes. The fast electron relaxation occurs via an efficient Auger-like electron–hole scattering mechanism. On the other hand, a small wave function overlap between core and shell states slows the hole relaxation. Additionally, holes can be trapped at the core/shell interface, leading to either slow detrapping or nonradiative recombination. Overall, these results demonstrate that it is crucial to construct devices enabling the injection of charge carriers energetically close to their emitting states in order to maximize the radiative efficiency of the system.
The quest for alternative energy sources has generated a world-wide effort to prepare materials and devices designed to harvest clean abundant energy resources such as solar radiation. Considerable interest has focused on hybrid photovoltaic systems combining an organic chromophore, conjugated polymer or dye, and an n-type inorganic semiconductor. [1][2][3] A suitable energy band offset between the organic and inorganic components ensures that photo-excited electronhole pairs formed near the organic/inorganic interface will dissociate into free carriers, with the electrons preferably on one component and the holes on the other. A promising hybrid donor-acceptor pair for photovoltaics are poly(p-phenylene vinylene) (PPV)-type conjugated polymers and titanium dioxide, [4,5] owing to the high optical absorption of the polymer in the visible range and the band offset at the titania/PPV interface, which induces electron transfer from the photo-excited polymer to titanium dioxide. To provide efficient exciton dissociation into charges prior to recombination, the phase separation between the organic and inorganic species must be on the same scale as the polymer exciton diffusion length, that is, 8-20 nm. [6,7] Furthermore, carrier transport to the electrodes requires that the organic and inorganic phases form continuous networks through the entire film.[8] The challenge is, therefore, to direct a donor-acceptor organic-inorganic phase separation on a sub-20 nm length scale, and at the same time obtain continuity and orientation of each individual phase on a much longer length scale. To achieve this goal we developed a new and general synthetic approach that employs the co-assembly of a titania precursor species, a conjugated polymer, and an amphiphilic structure-directing agent to form conjugated-polymerincorporated mesoscopically ordered titania films. The use of non-aqueous synthetic conditions enabled, for the first time, the incorporation of the highly hydrophobic conjugated polymers within the mesostructured titania host matrix during its formation. Judicious selection of the surface-active agent type and concentration directed the deposition of a cubically ordered through-film interpenetrating titania and semiconducting polymer networks with ca. 15 nm organic-inorganic phase separation. Incorporation of the conjugated polymer into the 3D titania matrix enhances its photostability, and integration of the novel hybrid material into a photovoltaic device results in improved device performances. This study demonstrates the ability to direct the self-organization of functional components into hierarchically ordered materials with improved characteristics for electronic and opto-electronic applications.Several approaches have been previously applied to prepare nanoscale interpenetrating conjugated-polymer/titania networks, but they typically lack at least one of the important characteristics, that is, the sub-20 nm organic-inorganic phase separation or the through-film connectivity. Mixing the semiconducting polymers wi...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.