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 lightinduced 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 factorsweak 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 photoresponsivity 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.

An emerging chalcogenide perovskite, CaZrSe 3 , holds promise for energy conversion applications given its notable optical and electrical properties. However, knowledge of its thermal properties is extremely important, e.g. for potential thermoelectric applications, and has not been previously reported in detail. In this work, we examine and explain the lattice thermal transport mechanisms in CaZrSe 3 using density functional theory and Boltzmann transport calculations. We find the mean relaxation time to be extremely short corroborating an enhanced phonon-phonon scattering that annihilates phonon modes, and lowers thermal conductivity. In addition, strong anharmonicity in the perovskite crystal represented by the Grüneisen parameter predictions, and low phonon number density for the acoustic modes, results in the lattice thermal conductivity to be limited to 1.17 W m −1 K −1. The average phonon mean free path in the bulk CaZrSe 3 sample (N → ∞) is 138.1 nm and nanostructuring CaZrSe 3 sample to~10 nm diminishes the thermal conductivity to 0.23 W m −1 K −1. We also find that p-type doping yields higher predictions of thermoelectric figure of merit than n-type doping, and values of ZT~0.95-1 are found for hole concentrations in the range 10 16-10 17 cm −3 and temperature between 600 and 700 K.

Combining first-principles calculations with the solution to the Boltzmann transport equations, we examine the lattice thermal transport for the orthorhombic perovskite BaZrS3 through analyses of phonon group velocities, lifetimes, average Grüneisen parameter, and Debye temperature. An extremely low lattice thermal conductivity (LTC) of 1.16 Wm–1 K–1 at 300 K is obtained with phonons at 0–4 THz being the main contributors. The acoustic phonons contribute ∼30% to the LTC, while the lower frequency range of the optical modes contributes the most. Nearly 83% of the accumulated LTC is contributed by phonons with MFP < 5 nm. Since the lattice parameter (9.98 Å) of BaZrS3 is not significantly different from the calculated MFP, we corroborate that nanostructuring might be ineffective to reduce LTC.

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Orthorhombic BaZrS3 is a potential optoelectronic material with prospective applications in photovoltaic and thermoelectric devices. While efforts exist on understanding the effects of elemental substitution and material stability, fundamental knowledge...