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We have investigated CdTe/CdS/In2O3:F/glass solar cell structures using quantitative SIMS for profiling the impurity distribution from the CdTe free surface through to the glass substrate. Ion implanted CdTe standards were used. The effect of the purity of the CdTe starting material was determined by studying two structures grown from 7N and 5N source materials. Particular emphasis was placed on the potentially electrically active impurities that may originate from the CdTe starting material, and are likely to affect the CdTe/CdS solar cell performance. It was shown that Cu, Zn, Sn, Sb and Pb profiles had the same level and shape in the CdTe layer regardless of the purity of the starting material used, and were therefore not originating from the starting material. Cl, O, Na and Si showed higher levels for structures grown using 5N purity CdTe compared to those from 7N, and may, at least in part, be due to the CdTe starting material used. It was also postulated that at least some impurities (in addition to Cl) may partially come from the CdCl2 treatment, and/or from the TCO (In) and glass (for Si and Na). Te and S interdiffusion at the CdTe/CdS interface was also shown to be enhanced when 5N CdTe source material is used as compared to 7N. [ABSTRACT FROM AUTHOR]

Defects in Au-catalysed CdTe nanowires vapour-liquid-solid-grown on polycrystalline underlayers have been critically evaluated. Their low-temperature photoluminescence spectra were dominated by excitonic emission with rarely observed above-gap emission also being recorded. While acceptor bound exciton lines due to monovalent metallic impurities (Ag, Cu or Na) were seen, only deeper, donor-acceptor-pair emission could be attributed to the Au contamination that is expected from the catalyst. Annealing under nitrogen acted to enhance the single crystal-like PL emission, whilst oxidizing and reducing anneals of the type that is used in solar cell device processing caused it to degrade. The incidence of stacking faults, polytypes and twins was related only to the growth axes of the wires (<111> 50%, <112> 30% and <110> 20%), and was not influenced by annealing. The potential electrical activity of the point and extended defects, and the suitability of these nanowire materials (including processing steps) for solar cell applications, is discussed. Overall they have a quality that is superior to that of thin polycrystalline films, although questions remain about recombination due to Au.