Using High-Resolution Anomalous-Scattering X-Ray Diffraction to Observe Off-Stoichiometric CU2ZnSnS4 Crystal Structures

Cu
₂
ZnSnS
₄
(CZTS) is a promising material for the absorber layer in sustainable thin film solar cells, but its photovoltaic performance is currently limited by low open-circuit voltage, due in part to crystal structure disorder. High-resolution anomalous-scattering X-ray diffraction is shown in this investigation to be a very useful tool for elucidating disordered CZTS crystal structures. Three of five samples fabricated over a range of composition by solid state reaction displayed two distinct CZTS phases at room temperature, evident in minute splitting of some peaks due to different c/a lattice parameter ratios. These are attributed to different composition types of CZTS, defined by the prevalence of different charge-neutral defect complexes. This work is the first report of XRD from CZTS at high-enough resolution to distinguish these phases distinctly and the disorder type attribution is only possible because anomalous-scattering XRD can uniquely differentiate between copper and zinc site occupancy.