Direct Insight into Grain Boundary Reconstruction in PolycrystallineCu(In,Ga)Se2with Atomic Resolution

Abstract

This work presents results from high-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy on twin boundaries (TBs) and nontwin grain boundaries (GBs) in $\mathrm{Cu}(\mathrm{In},\mathrm{Ga}){\mathrm{Se}}_2$ thin films. It is shown that the atomic reconstruction is different for different symmetries of the grain boundaries. We are able to confirm the model proposed by Persson and Zunger [Phys. Rev. Lett. 91, 266401 (2003)] for Se-Se-terminated $\Sigma 3$ $\{112\}$ TBs, showing Cu depletion and In enrichment in the two atomic planes closest to the TB. On the contrary, Cu depletion without In enrichment is detected for a cation-Se-terminated TB. At nontwin GBs, always a strong anticorrelation of Cu and In signals is detected suggesting that the formation of ${\mathrm{In}}_{\mathrm{Cu}}$ or ${\mathrm{Cu}}_{\mathrm{In}}$ antisites within a very confined region of smaller than 1 nm is an essential element in the reconstruction of these GBs. DOI: http://dx.doi.org/10.1103/PhysRevLett.108.075502 © 2012 American Physical Society