Grain boundaries are important in polycrystalline materials as they control the overall microstructural evolution and serve as both sinks and sources for dislocation activities in the material. Substituting crystalline atoms at the grain boundary region with amorphous intergranular films, it is possible to enhance dislocation absorption and so, reduce crack nucleation and growth at the interface. In this study, we have used Molecular Dynamics simulations to investigate the interface energy and their deformation mechanism under various mechanical loading of bi-crystal and polycrystal copper with the amorphous intergranular film. We have found that the presence of amorphous intergranular films reduces the interface energy and orientation dependence cannot be observed anymore. We have investigated both the effects of grain size (3 nm to 17 nm) and amorphous intergranular film thicknesses (0.5 nm to 1.5 nm). We have found a strong effect of the amorphous intergranular films in the strength of the material by causing a shift in the strongest grain size to a larger size. Moreover, we have found changes in the deformation mechanism due to the presence of the amorphous intergranular films from dislocation mechanism to grain boundary activity. Finally, thermal stability has been observed in the nanocrystalline copper with amorphous intergranular films during high-temperature creep.