Beyond Thin Films: Clarifying the Impact of -LiSi Formation in Thin Film, Nanoparticle, and Porous Si Electrodes.

The formation of the -LiSi phase has well-established detrimental effects on the capacity retention of thin film silicon electrodes. However, the role of this crystalline phase with respect to the loss of capacity is somewhat ambiguous in nanoscale morphologies. In this work, three silicon-based morphologies are examined, including planar films, porous planar films, and silicon nanoparticle composite powder electrodes.

Solvent Vapor Annealing, Defect Analysis, and Optimization of Self-Assembly of Block Copolymers Using Machine Learning Approaches.

Self-assembly of block copolymers (BCPs) is an alternative patterning technique that promises high resolution and density multiplication with lower costs. The defectivity of the resulting nanopatterns remains too high for many applications in microelectronics and is exacerbated by small variations of processing parameters, such as film thickness, and fluctuations of solvent vapor pressure and temperature, among others. In this work, a solvent vapor annealing (SVA) flow-controlled system is combined with design of experiments (DOE) and machine learning (ML) approaches.

Bipolar Resistive Switching in Junctions of Gallium Oxide and p-type Silicon.

In this work, native GaO is positioned between bulk gallium and degenerately doped p-type silicon (p-Si) to form Ga/GaO/SiO/p-Si junctions. These junctions show memristive behavior, exhibiting large current-voltage hysteresis. When cycled between -2.

Optimization of the Bulk Heterojunction of All-Small-Molecule Organic Photovoltaics Using Design of Experiment and Machine Learning Approaches.

All-small-molecule organic photovoltaic (OPV) cells based upon the small-molecule donor, DRCN5T, and nonfullerene acceptors, ITIC, IT-M, and IT-4F, were optimized using Design of Experiments (DOE) and machine learning (ML) approaches. This combination enables rational sampling of large parameter spaces in a sparse but mathematically deliberate fashion and promises economies of precious resources and time. This work focused upon the optimization of the core layer of the OPV device, the bulk heterojunction (BHJ).

van der Waals Epitaxy of Soft Twisted Bilayers: Lattice Relaxation and Mass Density Waves.

Interfaces comprising incommensurate or twisted hexagonal lattices are ubiquitous and of great interest, from adsorbed organic/inorganic interfaces in electronic devices, to superlubricants, and more recently to van der Waals bilayer heterostructures (vdWHs) of graphene and other 2D materials that demonstrate a range of properties such as superconductivity and ferromagnetism. Here we show how growth of 2D crystalline domains of soft block copolymers (BCPs) on patterned hard hexagonal lattices provide fundamental insights into van der Waals heteroepitaxy. At moderate registration forces, it is experimentally found that these BCP-hard lattice vdWHs do not adopt a simple moiré superstructure, but instead adopt local structural relaxations known as mass density waves (MDWs).

Water-soluble pH-switchable cobalt complexes for aqueous symmetric redox flow batteries.

A water soluble octahedral Co(ii) complex, BCPIP-Co(ii), with 4 appended carboxylic groups on the ligand periphery is utilized as both posolyte and negolyte in an aqueous, symmetric redox flow battery (RFB). The full RFB demonstrates coulombic efficiencies >99% for up to 100 cycles.

Redox Flow Batteries: How to Determine Electrochemical Kinetic Parameters.

Redox flow batteries (RFBs) are promising energy storage candidates for grid deployment of intermittent renewable energy sources such as wind power and solar energy. Various new redox-active materials have been introduced to develop cost-effective and high-power-density next-generation RFBs. Electrochemical kinetics play critical roles in influencing RFB performance, notably the overpotential and cell power density.

How To Optimize Materials and Devices via Design of Experiments and Machine Learning: Demonstration Using Organic Photovoltaics.

Most discoveries in materials science have been made empirically, typically through one-variable-at-a-time (Edisonian) experimentation. The characteristics of materials-based systems are, however, neither simple nor uncorrelated. In a device such as an organic photovoltaic, for example, the level of complexity is high due to the sheer number of components and processing conditions, and thus, changing one variable can have multiple unforeseen effects due to their interconnectivity.

Vapor-Phase Nanopatterning of Aminosilanes with Electron Beam Lithography: Understanding and Minimizing Background Functionalization.

Electron beam lithography (EBL) is a highly precise, serial method for patterning surfaces. Positive tone EBL resists enable patterned exposure of the underlying surface, which can be subsequently functionalized for the application of interest. In the case of widely used native oxide-capped silicon surfaces, coupling an activated silane with electron beam lithography would enable nanoscale chemical patterning of the exposed regions.

Methylammonium Cation Dynamics in Methylammonium Lead Halide Perovskites: A Solid-State NMR Perspective.

In light of the intense recent interest in the methylammonium lead halides, CHNHPbX (X = Cl, Br, and I) as sensitizers for photovoltaic cells, the dynamics of the methylammonium (MA) cation in these perovskite salts has been reinvestigated as a function of temperature via H, N, and Pb NMR spectroscopy. In the cubic phase of all three salts, the MA cation undergoes pseudoisotropic tumbling (picosecond time scale). For example, the correlation time, τ, for the C-N axis of the iodide salt is 0.

Understanding the Effects of a High Surface Area Nanostructured Indium Tin Oxide Electrode on Organic Solar Cell Performance.

Organic solar cells (OSCs) are a complex assembly of disparate materials, each with a precise function within the device. Typically, the electrodes are flat, and the device is fabricated through a layering approach of the interfacial layers and photoactive materials. This work explores the integration of high surface area transparent electrodes to investigate the possible role(s) a three-dimensional electrode could take within an OSC, with a BHJ composed of a donor-acceptor combination with a high degree of electron and hole mobility mismatch.