Compositional Inhomogeneity of Multinary Semiconductor Nanoparticles: A Case Study of Cu2ZnSnS4

Abstract

Probe-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the inter- and intraparticle compositional inhomogeneity of multinary Cu2ZnSnS4 (CZTS) nanoparticles. CZTS nanoparticles were prepared following three distinct synthesis protocols described in the literature. Strong fluctuations in composition were observed for Cu and Zn in individual nanoparticles, independent of the synthesis method. Certain particles have regions that have compositions close to that of Cu2SnS3, as well as, in the extreme case, the presence of nearly pure ZnS species. This is an observation that has not been reported in prior studies of these systems and underscores the need to both more carefully study the polydispersity of multinary semiconductor nanoparticles (MSNs) and to improve synthetic protocols and characterization of MSNs. Notably—despite the observation of compositional fluctuations in individual nanoparticles—reactive sintering in Se vapor was shown to reduce the nanoscale compositional fluctuations in the resulting sintered grains, facilitating the use of these heterogeneous particles in optoelectronic devices.