Short- and Long-Range Cation Disorder in (Ag _xCu_{1- x})₂ZnSnSe₄Kesterites

Understanding the nature of and controlling the cation disorder in kesterite-based absorber materials remain a crucial challenge for improving their photovoltaic (PV) performances. Herein, the combination of neutron diffraction and synchrotron-based X-ray absorption techniques was implemented to investigate the relationships among cation disorder, defect concentration, overall long-range crystallographic order, and local atomic-scale structure for (Ag_xCu_1-x)₂ZnSnSe₄(ACZTSe) material. The joint Rietveld refinement technique was used to directly reveal the effect of cation substitution and quantify the concentration of defects in Ag-alloyed stoichiometric and nonstoichiometric Cu₂ZnSnSe₄(CZTSe). The results showed that 10%-Ag-alloyed nonstoichiometric ACZTSe had the lowest concentration of detrimental antisite Cu_Zndefects (∼8 × 10¹⁹defects per cm^-3), which was two times lower than pristine and five times lower than the stoichiometric compositions. Moreover, Ag incorporation maintained the concentrations of beneficial Cu vacancies (V_Cu) and antisite Zn_Cudefects to >2 × 10²⁰defects per cm^-3. X-ray absorption measurements were performed to verify the degree of disorder through the changes in bond length and coordination number. Therefore, the incorporation of Ag into the CZTSe lattice could control the distribution of antisite defects, in the form of short- and long-range site disorder. This study paves the way to systematically understand and further improve the properties of kesterite-based materials for different energy applications.