The formation mechanism of cu(In_0.7 Ga_0.3)Se₂ nanoparticles and the densification trajectory of the se-rich quaternary target by hot pressing

In this paper, a method to obtain the CuInGaSe₂ (CIGS) absorber layer with an appropriate selenium content is put forward, in which a Se-rich target is used to deposit a CIGS thin-film and this film is annealed in a Se-free inert atmosphere. The key issue of this method is the preparation of a Se-rich target with a homogeneous composition and a high-density. The formation mechanism of CuInSe₂ and CuGaSe₂ is investigated and the results point to the intermediate phase Cu_2−x Se playing a role of a nucleation core. The sintering densification trajectory of the target with the addition of extra selenium is researched. Additionally, an effective way to avoid the sintering defects is proposed. Finally, a conversion efficiency of 11.2% for the CIGS solar cell is reached by sputtering from the obtained Se-rich target.