The substitution energies and migration energies of the alkali metal atoms of Li, Na, and K in CuInSe 2 (CIS) and CuGaSe 2 (CGS) were investigated by first-principles calculations. The substitution energies of Li, Na, and K atoms in CIS and CGS were calculated for two different cationic atom positions of Cu and In/Ga in the chalcopyrite unit cell. In CIS and CGS, the substitution energies of Na Cu are much lower than those of Na In and Na Ga . The substitution energies of the Li Cu atoms in CIS and CGS are lower than those of Na Cu , while the substitution energies of K Cu atoms in CIS and CGS are much higher than those of Na Cu . Therefore, it is difficult to form K Cu in CIS and CGS. The migration energies of Li, Na, and K atoms in CIS and CGS are obtained by a combination of the linear and quadratic synchronous transit (LST/QST) methods and the nudged elastic band (NEB) method. The theoretical migration energies of a Na atom at the Cu site to the nearest Cu vacancy (Na Cu G V Cu ) in CIS and CGS are much lower than those of (Cu Cu G V Cu ) in CIS and CGS. The mechanism underlying the alkali metal effect of Li, Na, and K in the CIGS film during the post-deposition treatment of LiF, NaF, and KF is discussed on the basis of the calculated substitution and migration energies.

The substitution energies and migration energies of the alkali‐metals of Li, Na, and K atoms in Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) were investigated by first‐principles calculations. The migration energies of Li, Na, and K atoms in CZTS and CZTSe are obtained by a combination of linear and quadratic synchronous transit (LST/QST) methods and a nudged elastic band (NEB) method. For CZTS and CZTSe, the substitution energies of NaCu and NaZn are much smaller than that of NaSn. The substitution energy of NaZn is comparable to that of NaCu, indicating that NaCu and NaZn are easily formed in CZTS and CZTSe. The substitution energies of the LiCu and LiZn atoms are smaller than those of NaCu and NaZn, while substitution energies of KCu and KZn atoms are much larger than those of NaCu and NaZn. Therefore, it is difficult to form KCu and KZnin CZTS and CZTSe. The theoretical migration energies of Na atom at Cu site to the nearest Cu vacancy (NaCu→VCu) and Na atom at Zn site to the nearest Cu vacancy (NaZn→VCu) are much smaller than those of (NaSn→VCu). The migration energies of (NaCu→VCu) and (NaZn→VCu) in CZTS and CZTSe are comparable to that of Na atom at Cu site to Cu vacancy (NaCu→VCu) in CIS. The mechanism for the alkali‐metal effect of Li, Na, and K in the Cu2ZnSn(S,Se)4 films during the post‐deposition treatment of LiF, NaF, and KF is discussed on the basis of the calculated substitution and migration energies. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)