Browsing by Subject "Nanocrystal assembly"

Now showing 1 - 3 of 3

Colloidal nanocrystal assemblies : self-organization, properties, and applications in photovoltaics
(2011-12) Goodfellow, Brian William; Korgel, Brian Allan, 1969-; Chelikowsky, James R; Dodabalapur, Ananth; Ekerdt, John G; Vanden Bout, David A
Colloidal nanocrystal assemblies offer an attractive opportunity for designer metamaterials. The ability to permute chemical composition, size, shape, and arrangement of nanocrystals leads to an astounding number of unique materials properties that find use in an extensive array of applications---ranging from solar cells to medicine. However, to take full advantage of these materials in useful applications, the nature of their assembly and their behavior under external stimuli must be well understood. Additionally, the assembly of colloidal nanocrystals into thin films provides a promising pathway to the solution-processing of inorganic materials that are prohibitively too expensive and/or difficult to deposit by conventional methods. Nanocrystal superlattices (NCSLs) of sterically stabilized nanocrystals were assembled by slow evaporation of colloidal dispersions on various substrates. Detailed analysis of the NCSL structures was carried out using transmission and scanning electron microscopy (TEM and SEM) and small-angle x-ray scattering (SAXS). Body-centered cubic (bcc) NCSLs, in particular, were studied in detail and ligand packing frustration was proposed as a significant driving force for their assembly. The behavior of NCSLs was also studied by SAXS under mild heating and solvent vapor exposure revealing several remarkable order-order, order-disorder, and amorphous-crystalline structural transitions. Colloidal Cu(In [subscript 1-x] Ga [subscript x])Se₂ (CIGS) nanocrystals were synthesized by arrested precipitation and formulated into inks. These inks were spray deposited into thin films under ambient conditions to serve as the active light absorbing material in printed low-cost photovoltaic (PV) devices. These devices, which were fabricated without the need for high temperature processes, have achieved power conversion efficiencies above 3 % under AM1.5 illumination. While the efficiencies of these devices are still too low for commercial viability, this work does provide a proof of concept that reasonable efficient solar cells can be created with a low-cost printable process using nanocrystal inks. Since high temperatures are not used to form the light-absorbing layer, nanocrystal-based solar cells were built on flexible light weight plastic substrates. The main obstacle to achieving high power conversation efficiencies was found to be the ability to extract the photo induced charge carriers. Nanocrystal films suffer from poor transport that leads to high recombination rates in thicker films. To date, the best efficiencies have been achieved with thin light absorber layers that only absorb a fraction of the incident light.
The assembly of inorganic nanocrystals using dynamic covalent chemistry
(2022-05) Dominguez, Manuel Nicholas; Milliron, Delia (Delia Jane); Truskett, Thomas M; Anslyn, Eric V; Rose, Michael
Here I show the work accomplished in my graduate career on metal oxide nanocrystals and their assembly into unique gels. Nanocrystals were synthesized using a well-established method that was adapted to improve subsequent functionalization. Collaborations between the Anslyn group led to ligands that were designed for tunable orthogonal covalent linkages between particles. Establishing a well solid foundation for controllable assembly through this collaboration was the goal, along with a better understanding of the system through collaboration with the Truskett lab and the work they do on simulations and theory. Applying what was learned and theorized into studying differences in similar systems for changes to the optical response also became a goal of the work presented. All put together an understanding of the building blocks of assembly, the assembly method, and finally the properties of the assembly are discussed within.
Understanding effects of disorder on the plasmonic response of nanoparticle assemblies
(2024-08) Green, Allison Marie ; Truskett, Thomas Michael,1973-; Milliron, Delia (Delia Jane); Guihua Yu; Nathaniel Lynd; Adrianne Rosales; Thomas Truskett
Rational design of macroscopic assemblies from nanoscale particles requires an understanding of how the individual particles or building blocks interact, and how their properties are modified by structural contributions across length scales. Advances in experimental strategies to assemble inorganic nanoparticles into spanning structures, such as uniform superlattice films or disordered gel networks, have led to increased interest in their use as functional materials. However, it is difficult to predict a priori how the characteristics of individual building blocks and the structure of the macroscopic assembly will impact a targeted property, limiting the ability to efficiently realize design goals. For example, the optical response of nanoparticle macro-assemblies is useful for applications in diagnostics and molecular detection, but designing these materials is challenging because how structure-dependent coupling impacts the plasmonic response of individual nanoparticles is not well understood. To understand and improve strategies for the design of functional nanoparticle assemblies, we employed both experimental and computational approaches. We began with the investigation of the influence of nanoparticle surface modifications on their interactions and assembly via depletions attractions. We systematically varied a polymer shell coating the nanocrystals and studied the resulting phase behavior in the presence of a polymer depletant, using X-ray scattering and coarse-grained molecular dynamics simulations. Different polymer shells result in different inter-nanocrystal interactions, microstructures, and, therefore, distinct optical and rheological responses. Next, to better understand how differences in disordered microstructures contribute to resulting optical responses, we developed a Brownian dynamics simulation model of two-dimensional nanoparticle monolayers spanning a range of structural defectivity. We used a mutual polarization method for the simulation of the far-field and near-field response of these heterogeneous assemblies of thousands of particles and capture how variations in local environments contribute to distributions of particle-level resonant frequencies in strong correlation with hot spot intensities. Understanding underlying nanoscale distributions help rationalize the emergent macroscale properties. Lastly, we extended this model to three-dimensional assemblies to study the importance of structural disorder in the coupling of plasmons and photons in a film, resulting in the emergence of polariton modes which can considerably increase near-field enhancement. While these modes become broadened and less well-defined with increasing disorder, the polariton dispersion relation is defect-tolerant. These findings highlight strategies for the design of disordered nanoparticle assemblies with targeted plasmonic responses, important for reducing experimental trial-and-error.