Indentation-induced cracking behavior of a Cu(In,Ga)Se2 films on Mo substrate

Cu(In,Ga)Se2 (CIGS) light absorption films were synthesized by co-sputtering method on Mo/soda-lime glass, and the mechanical behavior of the films was investigated by nanoindentation. The Young's modulus and hardness of the films were approximately 88.5 ± 2.2 and 5.89 ± 0.23 GPa, respectively. The comparison graph of indentation load–displacement curve with the curve based on the theoretical elastic films, while considering the curvature of the indenter tip, revealed that cracks initiated in the CIGS films at approximately 25 mN indentation load. The transmission electron microscopy (TEM) analysis revealed that most of the cracks exhibited intergranular fracture, and the fracture toughness of the films was ~0.22 MPa√m, which is greater than the brittleness of soda-lime glass. Both Palmqvist radial and lateral cracks are observed. Results also reveal that the indentation pressure caused grain subdivision (before cracking initiated), and indentation stress may be absorbed by relatively less dense microstructures of the films.