The development of bright, near-infrared-emissive quantum dots (QDs) is a necessary requirement for the realization of important new classes of technology. Specifically, there exist significant needs for brighter, heavy metal-free, near-infrared (NIR) QDs for applications with high radiative efficiency that span diverse applications, including down-conversion emitters for high-performance luminescent solar concentrators. We use a combination of theoretical and experimental approaches to synthesize bright, NIR luminescent InAs/InP/ZnSe QDs and elucidate fundamental material attributes that remain obstacles for development of near-unity NIR QD luminophores. First, using Monte Carlo ray tracing, we identify the atomic and electronic structural attributes of InAs core/shell, NIR emitters, whose luminescence properties can be tailored by synthetic design to match most beneficially those of high-performance, single-band-gap photovoltaic devices based on important semiconductor materials, such Si or GaAs. Second, we synthesize InAs/InP/ZnSe QDs based on the optical attributes found to maximize LSC performance and develop methods to improve the emissive qualities of NIR emitters with large, tunable Stokes ratios, narrow emission linewidths, and high luminescence quantum yields (here reaching 60 +/- 2%). Third, we employ atomistic electronic structure calculations to explore charge carrier behavior at the nanoscale affected by interfacial atomic structures and find that significant exciton occupation of the InP shell occurs in most cases despite the InAs/InP type I bulk band alignment. Furthermore, the density of the valence band maximum state extends anisotropically through the (111) crystal planes to the terminal InP surfaces/interfaces, indicating that surface defects, such as unpassivated phosphorus dangling bonds, located on the (111) facets play an outsized role in disrupting the valence band maximum and quenching photoluminescence.

Electrically conductive 3D periodic microscaffolds are fabricated using a particle-free direct ink writing approach for use as neuronal growth and electrophysiological recording platforms. A poly (2-hydroxyethyl methacrylate) (pHEMA)/pyrrole ink, followed by chemical in situ polymerization of pyrrole, enables hydrogel printing through nozzles as small as 1 μm. These conductive hydrogels can pattern complex 2D and 3D structures and have good biocompatibility with test cell cultures (~94.5% viability after 7 days). Hydrogel arrays promote extensive neurite outgrowth of cultured Aplysia californica pedal ganglion neurons. This platform allows extracellular electrophysiological recording of steady-state and stimulated electrical neuronal activities. In summation, this 3D conductive ink printing process enables preparation of biocompatible and micron-sized structures to create customized in vitro electrophysiological recording platforms.

Oxide-supported noble metal catalysts have been extensively studied for decades for the water gas shift (WGS) reaction, a catalytic transformation central to a host of large volume processes that variously utilize or produce hydrogen. There remains considerable uncertainty as to how the specific features of the active metal-support interfacial bonding—perhaps most importantly the temporal dynamic changes occurring therein—serve to enable high activity and selectivity. Here we report the dynamic characteristics of a Pt/CeO 2 system at the atomic level for the WGS reaction and specifically reveal the synergistic effects of metal-support bonding at the perimeter region. We find that the perimeter Pt 0 − O vacancy−Ce 3+ sites are formed in the active structure, transformed at working temperatures and their appearance regulates the adsorbate behaviors. We find that the dynamic nature of this site is a key mechanistic step for the WGS reaction.

Silicon heterojunction (SHJ) microcells offer a promising photovoltaic (PV) device for a wide range of micro-electronic applications due to their high performance potential. We examine two separate techniques for dicing SHJ microcells from bulk wafers: deep reactive ion etching (DRIE) and micro-laser cutting. We present the challenges and optimizations for each technique, as well as microcell performance for a 400µm x 400µm x 80µm microcell. Given the thickness of silicon wafers and the low face-to-edge area ratio for SHJ microcells of these dimensions, we consider varied illumination conditions for this structure. SHJ microcells are able to absorb photons along all surfaces; as such, we study microcell performance at each edge interface. We examine both modeled and experimental data of microcells across various lighting conditions and present high-performances for both sets of measurements.

We report the design, fabrication, and characterization of silicon heterojunction microcells, a new type of photovoltaic cell that leverages high-efficiency bulk wafers in a microscale form factor, while also addressing the challenge of passivating microcell sidewalls to mitigate carrier recombination. We present synthesis methods exploiting either dry etching or laser cutting to realize microcells with native oxide-based edge passivation. Measured microcell performance for both fabrication processes is compared to that in simulations. We characterize the dependence of microcell open-circuit voltage (Voc) on the cell area-perimeter ratio and examine synthesis processes that affect edge passivation quality, such as sidewall damage removal, the passivation material, and the deposition technique. We report the highest Si microcell Voc to date (588 mV, for a 400 μm × 400 μm × 80 μm device), demonstrate Voc improvements with deposited edge passivation of up to 55 mV, and outline a pathway to achieve microcell efficiencies surpassing 15% for such device sizes.

Abstract Solution‐phase syntheses of semiconductor nanoparticles provide a versatile and scalable approach to obtain nanomaterials with desirable structure and function. The most common mechanism invoked to explain the nucleation and growth of colloidal semiconductor nanocrystals is the LaMer model, an extension of classical nucleation theory. This model is widely used to conceptualize the conversion of molecular precursors into nanoparticles, and is characterized by three stages: monomer buildup, nucleation, and particle growth. Each of these stages represents a fundamental aspect of nanoparticle synthesis, and each has been widely studied over the past several decades. One of the core successes of this model has been the prediction of the “burst nucleation” method, which has enabled the synthesis of monodisperse nanoparticles in many material systems. Increasingly, however, it has become apparent that many chemical systems do not follow classical nucleation theory, but rather grow via nonclassical cluster‐mediated or aggregative growth processes. Regardless of the nucleation mechanism, highly monodisperse semiconductor nanoparticles can be obtained through kinetic size focusing or digestive ripening. Kinetic size focusing occurs during the nanoparticle growth phase when monomer concentration is high and smaller particles grow faster than their larger counterparts, enabling the smaller particles to “catch up” in size to give a more monodisperse ensemble. Digestive ripening, on the other hand, is a postsynthetic strategy where additional ligand is provided to the system to etch larger particles and redistribute monomer to smaller particles to get a more uniform sample. Beyond the synthesis of spherical colloidal nanoparticles, procedures can be modified to achieve a range of anisotropic structures including 1D nanorods and 2D nanosheets. Seeded and templated growth strategies can lend additional synthetic flexibility to more easily access a range of complex architectures. Continued innovation in synthetic methods and mechanistic understanding will pave the way for technological translation and lasting impact across applications from biological imaging to catalysis and many other next‐generation technologies.

Commercial smart window technologies for dynamic light and heat management in building and automotive environments traditionally rely on electrochromic (EC) materials powered by an external source. This design complicates building-scale installation requirements and substantially increases costs for applications in retrofit construction. Self-powered photoelectrochromic (PEC) windows are an intuitive alternative wherein a photovoltaic (PV) material is used to power the EC device, which modulates the transmission of the incident solar flux. The PV component in this application must be sufficiently transparent and produce enough power to efficiently modulate the EC device transmission. Here, we propose Si solar microcells (mu-cells) that are (i) small enough to be visually transparent to the eye and (ii) thin enough to enable flexible PEC devices. Visual transparency is achieved when Si mu-cells are arranged in high pitch (i.e., low-integration density) form factors while maintaining the advantages of a single-crystalline PV material (i.e., long lifetime and high performance). Additionally, the thin dimensions of these Si mu-cells enable fabrication on flexible substrates to realize flexible PEC devices. The current work demonstrates this concept using WO3 as the EC material and V2O5 as the ion storage layer, where each component is fabricated via sol-gel methods that afford improved prospects for scalability and tunability in comparison to thermal evaporation methods. The EC devices display fast switching times, as low as 8 s, with a modulation in transmission as high as 33%. Integration with two Si mu-cells in series (affording a 1.12 V output) demonstrates an integrated PEC module design with switching times of less than 3 min and a modulation in transmission of 32% with an unprecedented EC:PV areal ratio.

Nanoscale tetrapods were synthesized with independently tunable core and arm sizes and aspect ratios from a spectrum of quantum dot seeds, including ZnTe, CuInS2, InP, InP/ZnS, and Cd3P2. The range...

Cyclic voltammetry is demonstrated as a useful method to model equilibrium binding between quantum dots and redox active small molecules. Specifically, the interaction of a library of ferrocene derivatives with CdSe quantum dots is examined. For the strongly interacting systems, ferrocene carboxylic acid (FcCOOH) and ferrocene hexanethiol (Fc-hexSH), the binding equilibria can be quantitatively deduced by modeling the cyclic voltammetry data. This modeling allows extraction of the diffusion coefficients, equilibrium constants associated with both the reduced and oxidized species, and forward and reverse rates associated with binding for both the reduced and oxidized species. Taken together these data give direct insight into the binding of small molecules to quantum-dot surfaces as a function of oxidation state, critical information for the design of quantum dots as photoredox catalysts and charge transfer mediators.

Quantum dots are used as photoredox catalysts to drive bond cleavage in lignin model substrates. Cadmium selenide quantum dots selectively cleave C–O bonds with yields comparable to the best transi...

As the commercial display market grows, the demand for low-toxicity, highly emissive, and size-tunable semiconducting nanoparticles has increased. Indium phosphide quantum dots represent a promising solution to these challenges; unfortunately, they typically suffer from low inherent emissivity resulting from charge carrier trapping. Strategies to improve the emissive characteristics of indium phosphide often involve zinc incorporation into or onto the core itself and the fabrication of core/shell heterostructures. InP clusters are high fidelity platforms for studying processes such as cation exchange and surface doping with exogenous ions since these clusters are used as single-source precursors for quantum dot synthesis. Here, we examined the incorporation of zinc and gallium ions in InP clusters and the use of the resultant doped clusters as single-source precursors to emissive heterostructured nanoparticles. Zinc ions were observed to readily react with InP clusters, resulting in partial cation exchange, whereas gallium resisted cluster incorporation. Zinc-doped clusters effectively converted to emissive nanoparticles, with quantum yields strongly correlated with zinc content. On the other hand, gallium-doped clusters failed to demonstrate improvements in quantum dot emission. These results indicate stark differences in the mechanisms associated with aliovalent and isovalent doping and provide insight into the use of doped clusters to make emissive quantum dots.

The field of colloidal nanocrystal synthesis has progressed rapidly to the point where spherical colloids of diverse sizes and compositions are commercially available or can be synthesized with minimal synthetic training. As quantum dots work their way into a greater array of technologies, it has become increasingly important to maximize the uniformity of these nanoscale structures and the efficiency of associated photophysical processes. Anisotropic quantum nanocrystals and quantum confined heterostructures offer even greater customization and tunability of specific electronic and photonic properties compared to their spherical counterparts. However, synthetic access to these more advanced structures is less well understood, and existing synthetic approaches are often challenging to execute or replicate. This feature article provides an account of the various bottom-up and top-down methods that have been developed to prepare more complex quantum confined structures and highlights the progress that has been made in the preparation of colloidal semiconductor nanocrystal heterostructures. From this survey of existing methods, it becomes clear that seeded assembly of heterostructure architectures combines many of the advantages of both bottom-up and top-down approaches to enable the greatest potential control over a diversity of new, customizable heterostructures with added functionality.

Through empirical determination of precursor consumption rates for growing nanorods, a comprehensive rubric for the colloidal synthesis of customizable nanorods and their heterostructures is established.

The kinetic parameters governing cation exchange between molecular Cd2+ precursors and ZnTe nanorods is mapped out in detail to provide an all-inclusive rubric for tuning the rate and extent of cation exchange in this system—allowing for band gap tunability over a 1 eV range. Evaluation of cation exchange as a function of concentration, temperature, and time supports a mechanism involving initial, rapid Cd2+ adsorption followed by a rate determining cation exchange step with a measured activation energy of 24 kJ/mol. Provided there is sufficient cadmium to occupy the available surface sites, the solution concentration of cadmium has little influence on the rate of cation exchange, allowing the system to be modeled using pseudo-first-order kinetics, with observed rates ranging from 0.03 × 10–3 s–1 at 20 °C to 2.8 × 10–3 s–1 at 240 °C. It is also demonstrated that, due to the ease of cation exchange in these systems, previous claims of ZnTe/CdSe heterostructures are more accurately described as alloys.