  Organic-inorganic halide perovskites are intrinsically unstable when exposed
to moisture and/or light. Additionally, the presence of lead in many
perovskites raises toxicity concerns. Herein is reported a thin film of BaZrS3,
a lead-free chalcogenide perovskite. Photoluminescence and X-ray diffraction
measurements show that BaZrS3 is far more stable than methylammonium lead
iodide (MAPbI3) in moist environments. Moisture- and light-induced degradations
in BaZrS3 and MAPbI3 are compared by using simulations and calculations based
on density functional theory. The simulations reveal drastically slower
degradation in BaZrS3 due to two factors - weak interaction with water, and
very low rates of ion migration. BaZrS3 photo-detecting devices with
photo-responsivity of ~46.5 mA W-1 are also reported. The devices retain ~60%
of their initial photo-response after 4 weeks in ambient conditions. Similar
MAPbI3 devices degrade rapidly and show ~95% decrease in photo-responsivity in
just 4 days. The findings establish the superior stability of BaZrS3 and
strengthen the case for its use in optoelectronics. New possibilities for
thermoelectric energy conversion using these materials are also demonstrated.
