CdTe is a p--type semiconductor used in thin--film solar cells. To achieve high light--to-electricity conversion, annealing in the presence of CdCl 2 is essential, but the underlying mechanism is still under debate. Recent evidence suggests that a reduction in the high density of stacking faults in the CdTe grains is a key process that occurs during the chemical treatment. A range of stacking faults, including intrinsic, extrinsic and twin boundary, are computationally investigated to identify the extended defects that limit performance. The low--energy faults are found to be electrically benign, while a number of higher energy faults, consistent with atomic--resolution micrographs, are predicted to be hole traps with fluctuations in the local electrostatic potential. It is expected that stacking faults will also be important for other thin--film photovoltaic technologies.

Zinc nitride (Zn 3 N 2 ) is a promising candidate for optoelectronics applications due to its high electron mobility and high electrical conductivity. It is also thought that Zn 3 N 2 can be used as a starting material to achieve p-type conductivity in ZnO-based oxide homojunctions. In this work, the electronic structure of bulk Zn 3 N 2 is studied using density-functional theory (DFT) with different approximations to the exchange-correlation functional, ranging from (semi-)local functionals to the quasiparticle G 0 W 0 approach. We predict a bandgap in the range of 0.9-1.2 eV, reconciling the scattered values reported in experiments, and a remarkably low work function (ionisation potential) of 4.2 eV for the (111) surface. Fig. 5 (Color online) Total (TDOS) and projected (PDOS) density of states for Zn 3 N 2 calculated by HSE06 (as a benchmark) and PBE + U with different U eff values (ranging from 0 to 7 eV). The gray shade indicates TDOS obtained using the HSE06 functional, the red line TDOS using the PBE + U approach, and the blue dotted line PDOS of Zn 3d states using the PBE + U approach. The valence band edge is set to 0 eV. The appropriate U eff is then determined as 5 eV, matching the sub-valence band (near À8 eV) of HSE06 and PBE + U. We find this value of U eff ¼ 5 eV in close agreement with other Zn-based compounds, e.g. ZnO. [48][49][50] 3310 | RSC Adv., 2014, 4, 3306-3311This journal is

A first-principles description and prediction of brominated nanocrystals of Pd is presented. In particular, we conducted an extensive study of the adsorption behaviour of Br on various Pd surfaces (including both low and high Miller-index surfaces) as a function of its surface coverage. By coupling our calculated surface energies with ab initio (electrochemical) thermodynamics and the Gibbs-Wulff shape model, we find that the relative stability of the Pd surfaces is strongly modified by Br, allowing high Miller-index surfaces of Pd (namely the (210) surface) to become competitively favourable at moderate concentrations of Br. We also show that Pd nanoparticles assume a cube-like crystal shape at high concentrations of Br, exposing mainly the (100) facets with a Br surface coverage of 0.5 ML. This not only confirms and explains recent solution synthesis results, but also provides a quantitative atomic picture of the exposed surface facets, which is crucial in understanding the local surface chemistry of shape-controlled nanoparticles for better nanocatalyst design.

Fuel cells recombine water from H2 and O2 thereby can power, for example, cars or houses with no direct carbon emission. In anion‐exchange membrane fuel cells (AEMFCs), to reach high power densities, operating at high pH is an alternative to using large volumes of noble metals catalysts at the cathode, where the oxygen‐reduction reaction occurs. However, the sluggish kinetics of the hydrogen‐oxidation reaction (HOR) hinders upscaling despite promising catalysts. Here, the authors observe an unexpected ingress of B into Pd nanocatalysts synthesized by wet‐chemistry, gaining control over this B‐doping, and report on its influence on the HOR activity in alkaline conditions. They rationalize their findings using ab initio calculations of both H‐ and OH‐adsorption on B‐doped Pd. Using this “impurity engineering” approach, they thus design Pt‐free catalysts as required in electrochemical energy conversion devices, for example, next generations of AEMFCs, that satisfy the economic and environmental constraints, that is, reasonable operating costs and long‐term stability, to enable the “hydrogen economy.”