Leila Jewell, Frank Bridges, Sue A. Carter

University of California, Santa Cruz

Cu₂ZnSnS₄ (CZTS) is a promising material for thin film solar cells, yet a significant challenge remains in understanding the structures being formed, particularly in nanoparticles for solution-processible photovoltaic devices. We use the EXAFS technique to study the local structure and stoichiometry of as-made CZTS nanoparticles. We present K edge data and fits about each of the cations (Cu, Zn, Sn). The data reveal more Sn second neighbors than expected by the theoretical kesterite structure, even when each sample's metal concentrations are taken into account. The CZTS nanoparticles indicate antisite substitution, which is likely Sn on Cu sites and Zn on Sn sites. The Cu data also suggest additional clustering within the nanoparticle form. Understanding these differences in structure could be an important step in improving CZTS solar cells.