The characteristics of chemical bond and vacancy formation in chalcopyrite-type CuInSe2 were studied using first principles calculations. The chalcopyrite-type CuInSe2 had two kinds of chemical bond, Cu-Se and In-Se. The Cu-Se bond was a weak covalent bonding because electrons occupy both bonding and antibonding orbitals of Cu 3d and Se 4p and occupy only the bonding orbital (a1) of Cu 4s and Se 4p and do not occupy the antibonding orbital (a1*) of Cu 4s and Se 4p. On the other hand, the In-Se bond had a partially covalent and partially ionic character because the In 5s orbital covalently interacts with Se 4p; the In 5p orbital was higher than Se 4p and so the electron in the In 5p orbital moves to the Se 4p orbital. The average bond order of the Cu-Se and In-Se bonds could be calculated to be 1/4 and 1, respectively. The bond order of Cu-Se was smaller than that of In-Se. The characteristics of these two chemical bonds were related to the formation of Cu and In vacancies in CuInSe2. The formation energy of the Cu vacancy was smaller than that of the In vacancy under both Cu-poor and In-poor conditions. The displacement (Δl) of the surrounding Se atoms after the formation of the Cu vacancy was smaller than the Δl after the formation of the In vacancy.

Characteristics of Chemical Bond and Vacancy Formation in Chalcopyrite-Type CuInSe2 and Related Compounds. T.Maeda, T.Wada: Physica Status Solidi C, 2009, 6[5], 1312-6