Weyde Lin

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Lin

First Name

Weyde

ORCID

0000-0002-7572-499X

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Publications1 - 10 of 16

Nanocrystal superlattices as phonon-engineered solids and acoustic metamaterials
Yazdani, Nuri; Jansen, Maximilian; Bozyigit, Deniz; et al. (2019)
Nature Communications
Phonon engineering of solids enables the creation of materials with tailored heat-transfer properties, controlled elastic and acoustic vibration propagation, and custom phonon–electron and phonon–photon interactions. These can be leveraged for energy transport, harvesting, or isolation applications and in the creation of novel phonon-based devices, including photoacoustic systems and phonon-communication networks. Here we introduce nanocrystal superlattices as a platform for phonon engineering. Using a combination of inelastic neutron scattering and modeling, we characterize superlattice-phonons in assemblies of colloidal nanocrystals and demonstrate that they can be systematically engineered by tailoring the constituent nanocrystals, their surfaces, and the topology of superlattice. This highlights that phonon engineering can be effectively carried out within nanocrystal-based devices to enhance functionality, and that solution processed nanocrystal assemblies hold promise not only as engineered electronic and optical materials, but also as functional metamaterials with phonon energy and length scales that are unreachable by traditional architectures.
Recombination Dynamics in PbS Nanocrystal Quantum Dot Solar Cells Studied through Drift–Diffusion Simulations
Lin, Weyde; Yazdani, Nuri; Yarema, Olesya; et al. (2021)
ACS Applied Electronic Materials
The significant performance increase in nanocrystal (NC)-based solar cells over the last decade is very encouraging. However, many of these gains have been achieved by trial-and-error optimization, and a systematic understanding of what limits the device performance is lacking. In parallel, experimental and computational techniques provide increasing insights into the electronic properties of individual NCs and their assemblies in thin films. Here, we utilize these insights to parameterize drift–diffusion simulations of PbS NC solar cells, which enable us to track the distribution of charge carriers in the device and quantify recombination dynamics, which limit the device performance. We simulate both Schottky- and heterojunction-type devices and, through temperature-dependent measurements in the light and dark, experimentally validate the appropriateness of the parameterization. The results reveal that Schottky-type devices are limited by surface recombination between the PbS and aluminum contact, while heterojunction devices are currently limited by NC dopants and electronic defects in the PbS layer. The simulations highlight a number of opportunities for further performance enhancement, including the reduction of dopants in the nanocrystal active layer, the control over doping and electronic structure in electron- and hole-blocking layers (e.g., ZnO), and the optimization of the interfaces to improve the band alignment and reduce surface recombination. For example, reduction in the percentage of p-type NCs from the current 1–0.01% in the heterojunction device can lead to a 25% percent increase in the power conversion efficiency.
Impact of Cation Distribution on Photoluminescence of Ag-In-Se/ZnSe Core/Shell Nanocrystals
Moser, Annina; Yarema, Olesya; Rusch, Noemi; et al. (2025)
ACS Nanoscience Au
Ag–In–Se/ZnSe core/shell nanocrystals exhibit good photoluminescence quantum yield (PLQY), yet intriguingly, the maximum PLQY is first reached after several days of storage. We hypothesize that this may be due to cationic rearrangement in the nanocrystal post-synthesis. To test this hypothesis, we computationally generated ternary Ag–In–Se and quaternary Ag–In–Zn–Se nanocrystals with varying degrees of cationic disorder, as quantified by the distribution of the metal cation valence electrons in the tetrahedra around Se anions. We then used density functional theory-parametrized tight-binding simulations to study the electronic structure and optical properties of these systems as a function of the homogeneity of the valence electron distribution in a tetrahedron. We found that homogeneous distribution of cations leads to a larger band gap and optical coupling, and that, in the presence of Ag_In or In_Ag antisite defects, the introduction of intermediate valence Zn cations decreases the variance in valence electrons and improves the optical properties. We further simulated the impact of a Zn-gradient shell and rearrangement of cations in the outer layers of the nanocrystals and find that diffusion of Zn into the nanocrystal and cationic rearrangement can explain the post-synthetic increase of PLQY. This work highlights the importance of developing syntheses for multinary nanocrystals that result not only in size and composition uniformity but also in nanocrystals with a uniform distribution of charge.
Upscaling Colloidal Nanocrystal Hot-Injection Syntheses via Reactor Underpressure
Yarema, Maksym; Yarema, Olesya; Lin, Weyde; et al. (2017)
Chemistry of Materials
A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells
Bozyigit, Deniz; Lin, Weyde; Yazdani, Nuri; et al. (2015)
Nature Communications
Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic–organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current–voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode–nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices.
Transient Photovoltage Measurements in Nanocrystal-Based Solar Cells
Lin, Weyde; Bozyigit, Deniz; Yarema, Olesya; et al. (2016)
The Journal of Physical Chemistry C
Mapping the Atomistic Structure of Graded Core/Shell Colloidal Nanocrystals
Yarema, Maksym; Xing, Yunhua; Lechner, Rainer T.; et al. (2017)
Scientific Reports
Engineering the compositional gradient for core/shell semiconductor nanocrystals improves their optical properties. To date, however, the structure of graded core/shell nanocrystal emitters has only been qualitatively described. In this paper, we demonstrate an approach to quantify nanocrystal structure, selecting graded Ag-In-Se/ZnSe core/shell nanocrystals as a proof-of-concept material. A combination of multi-energy small-angle X-ray scattering and electron microscopy techniques enables us to establish the radial distribution of ZnSe with sub-nanometer resolution. Using ab initio shape-retrieval analysis of X-ray scattering spectra, we further determine the average shape of nanocrystals. These results allow us to generate three-dimensional, atomistic reconstructions of graded core/shell nanocrystals. We use these reconstructions to calculate solid-state Zn diffusion in the Ag-In-Se nanocrystals and the lattice mismatch between nanocrystal monolayers. Finally, we apply these findings to propose design rules for optimal shell structure and record-luminescent core/shell nanocrystals.
Cu-In-Te and Ag-In-Te colloidal nanocrystals with tunable composition and size
Yarema, Olesya; Yarema, Maksym; Lin, Weyde; et al. (2016)
Chemical Communications
Nanocrystal Quantum Dot Devices: How the Lead Sulfide (PbS) System Teaches Us the Importance of Surfaces
Lin, Weyde; Yarema, Maksym; Liu, Mengxia; et al. (2021)
Chimia
Semiconducting thin films made from nanocrystals hold potential as composite hybrid materials with new functionalities. With nanocrystal syntheses, composition can be controlled at the sub-nanometer level, and, by tuning size, shape, and surface termination of the nanocrystals as well as their packing, it is possible to select the electronic, phononic, and photonic properties of the resulting thin films. While the ability to tune the properties of a semiconductor from the atomistic- to macro-scale using solution-based techniques presents unique opportunities, it also introduces challenges for process control and reproducibility. In this review, we use the example of well-studied lead sulfide (PbS) nanocrystals and describe the key advances in nanocrystal synthesis and thin-film fabrication that have enabled improvement in performance of photovoltaic devices. While research moves forward with novel nanocrystal materials, it is important to consider what decades of work on PbS nanocrystals has taught us and how we can apply these learnings to realize the full potential of nanocrystal solids as highly flexible materials systems for functional semiconductor thin-film devices. One key lesson is the importance of controlling and manipulating surfaces.
Measuring the Vibrational Density of States of Nanocrystal-Based Thin Films with Inelastic X-ray Scattering
Yazdani, Nuri; Nguyen-Thanh, Tra; Yarema, Maksym; et al. (2018)
The Journal of Physical Chemistry Letters

Publications1 - 10 of 16

Weyde Lin

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