Control of Vacancy Defects in Reactively Sputtered (Ag,Cu)(In,Ga)Se2 Solar Cells

We report positron annihilation spectroscopy measurements revealing the prevalence of VSe-VCu divacancy defects in reactively sputtered ACIGS solar cells. Together with compositional and structural analysis as well as capacitance-voltage measurements, an intricate interplay is observed between divacancies, (Cu+Ag)/III ratio, grain size, and carrier concentration. These properties can be tuned during absorber growth by varying growth temperature and alkali content. Exploiting this interplay may be the key to achieving high efficiency in ACIGS solar cells.