Ti-Alloying of BaZrS₃ Chalcogenide Perovskite for Photovoltaics

BaZrS₃, a prototypical chalcogenide perovskite, has been shown to possess a direct band gap, an exceptionally strong near band edge light absorption, and good carrier transport. Coupled with its great stability, nontoxicity with earth-abundant elements, it is thus a promising candidate for thin film solar cells. However, its reported band gap in the range of 1.7–1.8 eV is larger than the optimal value required to reach the Shockley–Queisser limit of a single-junction solar cell. Here, we report the synthesis of Ba­(Zr_1–xTi_x)­S₃ perovskite compounds with a reduced band gap. It is found that Ti-alloying is extremely effective in band gap reduction of BaZrS₃: a mere 4 atom % alloying decreases the band gap from 1.78 to 1.51 eV, resulting in a theoretical maximum power conversion efficiency of 32%. Higher Ti-alloying concentration is found to destabilize the distorted chalcogenide perovskite phase.