월러스 아론

The chemistry of post transition metals is dominated by the group oxidation state N and a lower N-2 oxidation state, which is associated with occupation of a metal s(2) lone pair, as found in compounds of Tl(I), Pb(II) and Bi(III). The preference of these cations for non-centrosymmetric coordination environments has previously been rationalised in terms of direct hybridisation of metal s and p valence orbitals, thus lowering the internal electronic energy of the N-2 ion. This explanation in term

We report the first-principles electronic structure of BiVO 4, a promising photocatalyst for hydrogen generation. BiVO 4 is found to be a direct band gap semiconductor, despite having band extrema away from the Brillouin zone center. Coupling between Bi 6s and O 2p forces an upward dispersion of the valence band at the zone boundary; however, a direct gap is maintained via coupling between V 3d, O 2p, and Bi 6p, which lowers the conduction band minimum. These interactions result in symmetric hol

Abstract Quaternary semiconducting materials based on the kesterite (A 2 BCX 4 ) mineral structure are the most promising candidates to overtake the current generation of light‐absorbing materials for thin‐film solar cells. Cu 2 ZnSnS 4 (CZTS), Cu 2 ZnSnSe 4 (CZTSe) and their alloy Cu 2 ZnSn(Se,S) 4 consist of abundant, low‐cost and non‐toxic elements, unlike current CdTe and Cu(In,Ga)Se 2 based technologies. Zinc‐blende related structures are formed by quaternary compounds, but the complexity a

Bulk and surface sensitive x-ray spectroscopic techniques are applied in tandem to show that the valence band edge for In2O3 is found significantly closer to the bottom of the conduction band than expected on the basis of the widely quoted bulk band gap of 3.75 eV. First-principles theory shows that the upper valence bands of In2O3 exhibit a small dispersion and the conduction band minimum is positioned at Gamma. However, direct optical transitions give a minimal dipole intensity until 0.8 eV be

Hybrid halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) exhibit unusually low free-carrier concentrations despite being processed at low-temperatures from solution. We demonstrate, through quantum mechanical calculations, that an origin of this phenomenon is a prevalence of ionic over electronic disorder in stoichiometric materials. Schottky defect formation provides a mechanism to self-regulate the concentration of charge carriers through ionic compensation of charged point de

The performance of solar cells based on hybrid halide perovskites has seen an unparalleled rate of progress, while our understanding of the underlying physical chemistry of these materials trails behind. Superficially, CH₃NH₃PbI₃ is similar to other thin-film photovoltaic materials: a semiconductor with an optical band gap in the optimal region of the electromagnetic spectrum. Microscopically, the material is more unconventional. Progress in our understanding of

Degenerate $n$-type doping of semiconductors results in optical band-gap widening through occupation of the conduction band, which is partially offset by the so-called band-gap renormalization. From investigation of the magnitude and origin of these shifts through density-functional band-structure theory, we demonstrate that the key contribution to renormalization arises from the nonparabolic nature of the host conduction band but not the rigid shift of the band edges, as is the current paradigm