The recent development of organic halide perovskites such as CH3NH3PbI3 has led to a revolution in PV research. The power conversion efficiency (PCE) of solar cells made of this type of materials has witnessed an unprecedented rate of increase, from an initial PCE of 3.8% in 2009 to above 22% in 2016 . However, its instability and toxicity have led to major concerns on its viability as a mainstream PV absorber material. Nevertheless, the progress on halide perovskites has inspired us to search for novel semiconductor materials that can inherit the excellent optical and electronic properties of halides, while avoiding their severe limitations. As opposed to their oxide and halide siblings, chalcogenide perovskites with the chemical formula of ABX3, where A represents an alkaline earth element such as Ca, Sr and Ba; B represents a group IVB element such as Ti, Zr and Hf, and X is S and Se, received little attention. Recently, our theoretical investigation found that the chalcogenide perovskites can be a direct band gap semiconductor with strong light absorption and good carrier transport, with potential of defect tolerance . In this work, we present our results on the synthesis and characterization of chalcogenide perovskites, in particular BaZrS3, by high temperature sulfurization of their oxide counterparts . Their crystal structures were identified by XRD and composition by EDX. UV-vis measurements confirmed that they are semiconductors with band gap value of 1.7-1.8 eV, consistent with theoretical predictions. High pressure Raman studies show that the perovskite phase is stable against volume compression, with the band gap value decrease with increasing pressure . This suggests that by alloying cations with smaller radius such as Ti, it is possible to reduce the band gap. Subsequent experiments show that a moderate Ti incorporation reduces the band gap to 1.5 eV. Finally, we show our preliminary results on the growth of chalcogenide perovskite thin films.
 The NREL Research Cell Efficiency Records (http://www.nrel.gov/ncpv/).
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 N. Gross et al. “Stability and band gap tuning of the chalcogenide perovskite BaZrS3 in Raman and optical investigations at high pressure”, Phys. Rev. Appl., accepted.