|英文要約||Title: Development of high-efficiency CZTS solar cells and submodules (FY2012-FY2014) FY2013 Annual Report
We have investigated the migration energy of Cd atom in CuInSe2 (CIS) with a Cu vacancy by first-principles calculations. The activation energy of Cd migration in CIS and migration pathways are obtained by means of the combination of LST/QST and NEB methods. The migration energy of Cd atom (Cd→VCu) in CIS (0.99 eV) is comparable to that of Cu migration (Cu→VCu) in CIS (1.06 eV). This result indicates that Cd diffusion in CIS easily occurs like Cu diffusion. Then we investigated the substitution energy and migration energy of a Na atom in CIS and CGS. The theoretical migration energy of NaCu to the Cu vacancy (NaCu→VCu) in CIS is 0.31 eV. The migration energy of a Na atom (Na→VCu) in CIS is considerably smaller than that of a Cu atom (Cu→VCu) in CIS (1.06 eV). However, the substitution energy of NaCu in CIS (0.78 eV) is a positive value and much larger than the formation energy of the Cu vacancy in CIS. Therefore, a Na atom in CIS can easily migrate to the position of the Cu vacancy. Then, a small amount of Na substitution can occur in CIS crystal.