Effect of Ag incorporation on structure and optoelectronic properties of (Ag1-xCux)2ZnSnSe4 solid solutions

The performance of Cu2ZnSnSe4 solar cells is presently limited by low values of open-circuit voltage which are a consequence of strong band tailing and high level of non-radiative recombination. Recently, the partial substitution of Cu, Zn and Sn by other elements has shown potential to overcome this limitation. We explored the structural changes and the effect on the optoelectronic properties of the partial substitution of Cu with Ag in Cu2ZnSnSe4. This study clarifies the crystal structure of (Ag1-xCux)2ZnSnSe4 solid solution series, deducing possible cationic point defects and paying special attention to the presence of Cu/Zn disorder with a combination of neutron and X-ray diffraction. The optoelectronic properties of the solid solution series are assessed using reflection and quantitative photoluminescence spectroscopy, which allows us to estimate the fraction of non-radiative recombination, which would contribute to the open-circuit voltage loss in devices. The results strongly suggest Ag incorporation as a promising route to eliminate Cu/Zn disorder and to reduce non-radiative recombination losses in Cu2ZnSnSe4