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Ab initio approaches to electronic excitations in materials for thin-film solar cells

Authors: S. Botti

Ref.: Theory Seminars at Fritz-Haber Institut, Berlin (Germany), 15/7/2010 (2010)

Abstract: 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. Moreover, thin film solar cells require transparent contacts. In practice, these contacts are built from insulating oxides that for a certain range of doping become conductive while retaining transparency in the visible spectrum. Thin films of compounds of the delafossite family, namely Cu(Al,Ga,In)O$_2$, are particularly interesting as they show bipolar conductivity. This opens the way for a new technology entirely based on transparent electronics, with innovative applications such as transparent screens, stacked solar cells or functional windows that generate electricity. The origin of the exceptional electronic properties of these two classes of materials is still not well understood, despite the large amount of experimental and theoretical works dedicated to this purpose. This is a serious restraint when it comes to designing new materials for more efficient photovoltaic energy conversion. In this context, can ab-initio calculations of electronic excitations give a crucial contribution? Which theoretical approaches yield the best compromise between efficiency and accuracy? In this seminar I will try to give an answer to these questions.