The structure of TlGaSe2 has been studied by triple-crystal X-ray scattering techniques. At room temperature in the paraelectric phase the structure is believed to be C2/c, but the authors found that some of the (h, h, l) Bragg reflections, those with h odd, are broadened along the c* direction. This is shown to arise because of faults in the stacking of the atomic sheets perpendicular to c*. A simple model is developed for the scattering which suggests that on average a stacking fault occurs in the single crystal about once every four planes. Between 117 and 110 K the crystal has an incommensurate structure with a wavevector ( delta , delta , 1/4) where delta approximately=0.02 reciprocal lattice units. At 110 K, delta jumps discontinuously to zero to produce a commensurate phase. These results confirm the earlier suggestions of an incommensurate phase in TlGaSe2.

The conversion efficiency of as-deposited, CdTe solar cells is poor and typically less than 5%. A CdCl2 activation treatment increases this to up to 22%. Studies have shown that stacking faults (SFs) are removed and the grain boundaries (GBs) are decorated with chlorine. Thus, SF removal and device efficiency are strongly correlated but whether this is direct or indirect has not been established. Here we explain the passivation responsible for the increase in efficiency but also crucially elucidate the associated SF removal mechanism. The effect of chlorine on a model system containing a SF and two GBs is investigated using density functional theory. The proposed SF removal mechanisms are feasible at the 400 ∘C treatment temperature. It is concluded that the efficiency increase is due to electronic effects in the GBs while SF removal is a by-product of the saturation of the GB with chlorine but is a key signal that sufficient chlorine is present for passivation to occur.

No abstract

The drawing of the ferromagnetic spin chains in Fig. 1͑c͒, shown as blue ͑dark gray͒ lines, was incorrect and should be replaced by the new figure provided here. Previously, by mistake, the ferromagnetic spin chains had segments which were not parallel to the in-plane lobes of the d x 2 −z 2 / d y 2 −z 2-like orbitals, whereas in the rest of the paper, including the calculations, the correct spin chains were assumed.

Cadmium telluride (CdTe) solar cells are deposited in current production using evaporation-based tech- niques. Fabricating CdTe solar cells using magnetron sputtering would have the advantage of being more cost-efficient. Here, we show that such deposition results in the incorporation of the magnetron working gas Ar, within the films. Post deposition processing with CdCl 2 improves cell efficiency and during which stacking faults are removed. The Ar then accumulates into clusters leading to the creation of voids and blisters on the surface. Using molecular dynamics, the penetration threshold energies are determined for both Ar and Xe, with CdTe in both zinc-blende and wurtzite phases. These calculations show that more Ar than Xe can penetrate into the growing film with most penetration across the (111) surface. The mechanisms and energy barriers for interstitial Ar and Xe diffusion in zinc-blende are determined. Barriers are reduced near existing clusters, increasing the probability of capture-based cluster growth. Barriers in wurtzite are higher with non-Arrhenius behaviour observed. This provides an explanation for the increase in the size of voids observed after stacking fault removal. Blister exfoliation was also modelled, showing the formation of shallow craters with a raised rim.