[en] Stacking-fault energy (SFE) is a critical parameter that influences plastic deformation of Cu alloys. Here, the SFEs of Cu solid solutions at various temperatures and solute concentrations were studied by using first-principles calculations. The interaction energies of 18 substitutional atoms and 5 interstitial atoms with stacking fault (SF) in Cu were obtained for the first time. The results show that the interactions can extend to the second layer with respect to the SF. Substitutional atoms Sn, Al, Zn, P, Si, Ge as well as interstitial atoms Be, C, N, O, H have large attraction energies with the SF; whereas, substitutional atoms Ti, Mn, Cr are repelled by the SF, and the rest of the atoms have small interaction energies. Then, the effects of uniform and Fermi-Dirac distribution of solute atoms on the SFE of Cu alloys were further investigated based on these interaction energies. It is found that the SFE of Cu can be drastically reduced by Sn, Al, Zn, P, Si, Ge, C, N and O atoms with relatively high concentration at low temperatures. Our research suggests that it is possible to obtain twins in bulk Cu by adding alloying elements at circumstances, since the SFEs can be significantly lowered. - Highlights: • The atoms attracted by SFs can significantly reduce the SFEs of Cu solid solutions. • A few substitutional solutes can greatly lower the SFEs of Cu at low temperatures. • At low temperatures, some interstitial solutes may drastically decrease the SFEs. • The possibility of gaining twins in bulk Cu is increased under certain conditions.