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DS: Fachverband Dünne Schichten

DS 17: Focus Session: Thin Film Photovoltaic Materials and Solar Cells I

DS 17.4: Topical Talk

Mittwoch, 13. März 2013, 11:15–11:45, H32

Intrinsic point defects in CuInSe₂ and CuGaSe₂ studied by screened-exchange hybrid density functional theory — •Karsten Albe und Johan Pohl — TU Darmstadt, Instititut für Materialwissenschaft, FG Materialmodellierung, Petersenstr. 32, D-64287 Darmstadt

Cu(In,Ga)Se₂ is one of the most promising absorber material for solar cells. However, the presence of intrinsic point defects can be detrimental to the device properties, because of intrinsic doping and the formation of trap levels. These may act as recombination centres and therefore limit the device efficiency. Therefore, an in-depth understanding of the role of point defects in these devices is essential for optimizing the solar cell efficiency. In this talk, we discuss all relevant intrinsic point defects in terms of their defect formation energies, their charge transition levels and their localized single-particle states in the band gap, where applicable. First, the role of copper vacancies and interstitials for copper diffusion and Fermi-level pinning in the material will be discussed. Then Cu_In and Cu_Ga antisites are investigated and identified as hole traps with two distinct levels within the band gap, one of which can be attributed to the experimentally observed N2 level. Ga_Cu is confirmed as a deep defect in CuGaSe₂ and complex formation of antisites with copper vacancies is found not to be decisive for explaining the favourable properties of CuInSe₂, since In_Cu is already shallow by itself. The results also raise doubts about the relevance of selenium vacancies and DX centers for experimentally observed metastabilities.