### Session A29: Physics and Materials for Inorganic Photovoltaics: I

8:00 AM–10:48 AM, Monday, March 15, 2010
Room: C123

Chair: Tonio Buonassis, Massachusetts Institute of Technology

Abstract ID: BAPS.2010.MAR.A29.9

### Abstract: A29.00009 : Multivalency of Sn in Cu$_{2}$ZnSnS$_{4}$

10:00 AM–10:12 AM

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#### Authors:

Koushik Biswas
(National Renewable Energy Laboratory)

Stephan Lany
(National Renewable Energy Laboratory)

Alex Zunger
(National Renewable Energy Laboratory)

The highly efficient ternary chalcopyrites such as 2(CuInSe$_{2})$ = Cu$_{2}$In$_{2}$Se$_{4}$ can be replaced as absorber materials in photovoltaic cells by Cu$_{2}$ZnSnS$_{4}$ (band gap $\sim$ 1.5 eV) in order to avoid the costly element In. Yet, the question remains whether a Fermi-level pinning defect can form spontaneously in these quaternary materials just as the In$_{Cu}$ intrinsic \textit{DX} centers in CuInSe$_{2}$ [1]. Here we study theoretically the deep gap levels introduced by the Sn$_{Cu}$ and Sn$_{Zn}$ defects in Cu$_{2}$ZnSnS$_{4}$. We find that these originate from the multi-valency of Sn, which can change into a +II oxidation state instead of the normal +IV state. Such a transition can even occur for Sn on its native site. Thus, we compare to the respective defect behavior in the kesterite Cu$_{2}$ZnGeSe$_{4}$, which has a similar band gap, but a less pronounced multi-valency of the respective IV-valent element Ge. \\[4pt] [1] S. Lany and A. Zunger, Phys. Rev. Lett. 100, 016401 (2008).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2010.MAR.A29.9