Entropy-Driven Clustering in Tetrahedrally Bonded Multinary Materials

Compositional inhomogeneities in multielemental materials typically form due to lowering of the energy relative to the homogeneous phase. Here, we demonstrate an entropy-driven mechanism in the zinc-blende derived cation-substituted multinary compounds Cu2SnS3 (CTS) and Cu2ZnSnS4 (CZTS). Using a motifbased model Hamiltonian and Monte Carlo simulations, we find that disorder leads to a redistribution of the structural motifs in such a way to create cation clustering. The associated formation of (sub-) nanometerscale compositional inhomogeneities can cause potential fluctuations with detrimental consequences for photovoltaic applications.