Quaternary
chalcogenide copper zinc tin sulfide (CZTS) nanoparticles
are used to make the p-type absorber layer in CZTS solar cells, which
are considered more benign alternatives to those based on cadmium
telluride (CdTe) and less expensive than copper indium gallium selenide.
CZTS has an ideal band gap and a high absorption coefficient for solar
radiation, making the nanoparticles an attractive option for photovoltaic
cells. In this work, we explore the toxicity of CZTS nanoparticles
using an environmentally relevant bacterial model Shewanella
oneidensis MR-1. This study also focuses on understanding
the stability of CZTS-based thin films and their direct interaction
with bacterial cells. Bacterial cell viability, stability of nanoparticles
and thin films, as well as mechanisms of toxicity were evaluated using
various analytical tools. The CZTS nanoparticle suspensions show significant
acute toxic effects on bacterial cells, but long-term (72 h) exposure
of bacterial cells to CZTS-based thin films (made from nanoparticles)
do not exhibit similar detrimental impacts on bacterial viability.
This result is compelling because it suggests that CZTS nanomaterials
will have minimal unintended toxicity as long as they are incorporated
into a stable film structure.