Characterization of Ag(In, Ga)Se2/CdS interface in AIGS solar cell by HAADF-STEM measurement

An Ag(In, Ga)Se₂ (AIGS) absorber layer of AIGS solar cell was deposited by a three-stage method and other layers were also fabricated to complete the integrated solar cell structure. The interface between the AIGS film and CdS buffer layer was investigated using bright field scanning transmission electron microscopy (BF-STEM) and high-angle annular dark field (HAADF) scanning transmission electron microscopy imaging (STEM). In the HAADF-STEM measurement, since electrons are directly scattered by atoms, they are very sensitive to atomic numbers and specimen density. Therefore, the imaging mechanism in HAADF-STEM is different from the conventional TEM measurement and lattice can be reflected directly. As a result, HAADF-STEM and BF-STEM can be complementary to each other, which is helpful for researching material properties. In this work, it was found in the HAADF-STEM studies that the AIGS layer consisted of Ag-rich and Ag-poor layers, which is a new finding for AIGS film grown by three-stage method. At the AIGS/CdS interface, there are some defects and lattice arrangement was distorted, resulting in the poor solar cell performance of AIGS compared with the CIGS solar cell.