Ab initio study of electronic excitations in materials for thin-film solar cells
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During the past years, Cu(In,Ga)(Se,S)2 (CIGS) thin-film solar cells emerged as
a technology that could challenge the current hegemony of silicon solar panels.
CIGS compounds conserve to a very high degree their electronic properties in a
large non-stoichiometric range and are remarkably insensitive to radiation
damage or impurities. The family of kesterites Cu2ZnSe(S,Se)4 exhibits very
similar electronic properties. Moreover, kesterites have the clear advantage of
being composed of abundant, non-toxic, less expensive chemical elements.
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The origin of the exceptional electronic properties and the defect physics of
these complex materials is still not completely understood, despite the large
amount of experimental and theoretical work dedicated to that purpose. In
particular, standard density functional theory yields often results in
quantitative and qualitative disagreement with experiments. This is a serious
problem when it comes to designing new materials for more efficient photovoltaic
energy conversion.
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In this context, can ab-initio calculations of electronic excitations beyond
ground-state density functional theory give a crucial contribution?
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By presenting some examples of calculations, I will discuss which theoretical
approaches are reliable, at a reasonable computational cost, and what is the
physical insight that they allow to gain on electronic excitations in new
materials for photovoltaics. Finally, I will present an example of application
of material design, that represents at present the new frontier in the field of
theoretical material science. Using the minima hopping method, we found and
characterized new low-enthalpy phases of silicon with almost-direct band gaps
and displaying strong absorption in the visible.
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References:
1 J. Vidal, S. Botti, P. Olsson, J-F. Guillemoles, and L. Reining, Phys. Rev.
Lett., 2010, 104, 056401.
2 J. Vidal, F. Trani, F. Bruneval, M.A.L. Marques, and S. Botti, Phys. Rev.
Lett., 2010, 104, 136401.
3 S. Botti, D. Kammerlander, and M.A.L. Marques,  Appl. Phys. Lett., 2011, 98,
241915.
4 I. Aguilera, J. Vidal, P. Wahnón, L. Reining, and S. Botti
Phys. Rev. B, 2011, 84, 085145.
S. Botti, J.A. Flores-Livas, M. Amsler, S. Goedecker, M.A.L. Marques
submitted (2012) http://arxiv.org/abs/1203.5669v1