Maria K Y Chan

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Despite the many advantages (e.g., suitable band gap, exceptional optical absorptivity, earth abundance) of pyrite as a photovoltaic material, its low open-circuit voltage (OCV) has remained the biggest challenge preventing its use in practical devices. Two of the most widely accepted reasons for the cause of the low OCV are (i) Fermi level pinning due to(More)
Citation Sun, Ruoshi et al. " Intrinsic stoichiometry and oxygen-induced p-type conductivity of pyrite FeS_{2}. " Physical Review B 84 Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available.(More)
Pyrite (FeS2), being a promising material for future solar technologies, has so far exhibited in experiments an open-circuit voltage (OCV) of around 0.2 V, which is much lower than the frequently quoted 'accepted' value for the fundamental bandgap of ∼0.95 eV. Absorption experiments show large subgap absorption, commonly attributed to defects or structural(More)
An efficient method for the prediction of fundamental band gaps in solids using density functional theory (DFT) is proposed. Generalizing the Delta self-consistent-field (ΔSCF) method to infinite solids, the Δ-sol method is based on total-energy differences and derived from dielectric screening properties of electrons. Using local and semilocal(More)
Layered molybdenum disulfide has demonstrated great promise as a low-cost alternative to platinum-based catalysts for electrochemical hydrogen production from water. Research effort on this material has focused mainly on synthesizing highly nanostructured molybdenum disulfide that allows the exposure of a large fraction of active edge sites. Here we report(More)
Silicon is of significant interest as a next-generation anode material for lithium-ion batteries due to its extremely high capacity. The reaction of lithium with crystalline silicon is known to present a rich range of phenomena, including electrochemical solid state amorphization, crystallization at full lithiation of a Li(15)Si(4) phase, hysteresis in the(More)
Molecular surfaces at atomic and subatomic scales are inherently ill-defined. In many computational chemistry problems, boundaries are better represented as volumetric regions than as discrete surfaces. Molecular structure of a system at equilibrium is given by the self-consistent field, commonly interpreted as a scalar field of electron density. While(More)
A lack of consensus persists regarding the origin of photoluminescence in silicon nanocrystals. Here we report pressure-dependences of X-ray diffraction and photoluminescence from alkane-terminated colloidal particles. We determine the diamond-phase bulk modulus, observe multiple phase transitions, and importantly find a systematic photoluminescence red(More)
To evaluate the possible utility of single layer graphene for applications in Li ion batteries, an extensive series of periodic density functional theory (DFT) calculations are performed on graphene sheets with both point and extended defects for a wide range of lithium coverages. Consistent with recent reports, it is found that Li adsorption on defect-free(More)
Silicon has become an intriguing anode material in lithium ion secondary batteries because of its theoretical high gravimetric and volumetric capacity for lithiation (i.e., 4200 and 1750 mA h cm − 3 , respectively). [ 1–6 ] To approach the theoretical limits, the conductivity of lithium in silicon should be high because the diffusion rate of lithium in and(More)