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Electronic properties of materials for thin-film solar cells: Which ab initio approaches can we trust?

Authors: S. Botti

Ref.: “French-American Young Engineering Scientists Symposium 2009”, Synchrotron Soleil, France, 16/11/2009 (2009)

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. 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 are reliable? In my talk I will try to give an answer to these questions.