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We study the use of cadmium telluride (CdTe) nanocrystal colloids as a solution-processable "ink" for large-grain CdTe absorber layers in solar cells. The resulting grain structure and solar cell performance depend on the initial nanocrystal size, shape, and crystal structure. We find that inks of predominantly wurtzite tetrapod-shaped nanocrystals with arms ∼5.6 nm in diameter exhibit better device performance compared to inks composed of smaller tetrapods, irregular faceted nanocrystals, or spherical zincblende nanocrystals despite the fact that the final sintered film has a zincblende crystal structure. Five different working device architectures were investigated. The indium tin oxide (ITO)/CdTe/zinc oxide structure leads to our best performing device architecture (with efficiency >11%) compared to others including two structures with a cadmium sulfide (CdS) n-type layer typically used in high efficiency sublimation-grown CdTe solar cells. Moreover, devices without CdS have improved response at short wavelengths.

CdTe-based solar cells exhibiting 19% power conversion efficiency were produced using widely available thermal evaporation deposition of the absorber layers on SnO 2 -coated glass with or without a transparent MgZnO buffer layer. Evaporating CdSe and CdTe sequentially by thermal evaporation and subsequent CdCl 2 annealing establishes efffective CdSeTe band grading as well as dense, large-grain films. These results show that high-performance II−VI photovoltaics can be made by inexpensive, commercially available evaporation systems without the need to build customized equipment, enabling CdTe photovoltaics research and manufacturing to be more accessible to the broader photovoltaics community.

The synchrotron x-ray absorption near edge structures (XANES) technique was used in conjunction with first-principles calculations to characterize Al-doped ZnO films. Standard characterizations revealed that the amount of carrier concentration and mobility depend on the growth conditions, i.e. H 2 ðor O 2 Þ=Ar gas ratio and Al concentration. First-principles calculations showed that Al energetically prefers to substitute on the Zn site, forming a donor Al Zn , over being an interstitial (Al i ). The measured Al K-edge XANES spectra are in good agreement with the simulated spectra of Al Zn , indicating that the majority of Al atoms are substituting for Zn. The reduction in carrier concentration or mobility in some samples can be attributed to the Al Zn -V Zn and 2Al Zn -V Zn complex formations that have similar XANES features. In addition, XANES of some samples showed additional features that are the indication of some -Al 2 O 3 or nAl Zn -O i formation, explaining their poorer conductivity.

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