STRUCTURE AND DEFECT CHEMISTRY OF GRAIN-BOUNDARIES IN CUINSE2

Geometrical models for simple grain boundary structures in the CuInSe2 lattice are developed. A number of structural units are derived which can be used to describe random grain boundaries. A typical feature is the occurrence of six incorrect cation-cation (Cu-In) and anion-anion (Se-Se) bonds. The energy of the incorrect bonds is estimated and used to determine the formation energies of vacancies and antisite defects in the bulk and at grain boundaries. The predominant intrinsic point defects are described and differ in single-crystal and polycrystalline materials. The results give some insight into the electrical properties of grain boundaries and their interaction with intrinsic point defects. They are discussed from the perspective of the electrical properties of polycrystalline thin films.