Short- and Long-Range Cation Disorder in (AgxCu1-x)(2)ZnSnSe4 Kesterites

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 (AgxCu1-x)(2)ZnSnSe4 (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-Zn defects (similar to 8 x 1019 defects 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-Cu defects to >2 x 10(20) defects 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.

Automated summary

Understanding and controlling cation disorder in kesterite-based absorber materials is crucial for improving their photovoltaic performance. This study used neutron diffraction and synchrotron-based X-ray absorption techniques to investigate the relationships among cation disorder, defect concentration, crystallographic order, and atomic-scale structure. The results showed that incorporating silver into the material could reduce the concentration of detrimental defects and maintain the concentration of beneficial defects, thus controlling the defect distribution in the lattice.