Measuring and Controlling the Electronic Transport Properties of BaZrS₃ Chalcogenide Perovskite Thin Films

Chalcogenide perovskites are an emerging class of semiconductor materials that are of interest for optoelectronic applications, and especially for photovoltaics (PV). Within this broader class of materials, BaZrS₃ (BZS) is the most widely-studied to date, showing several promising properties for PV application. BZS consists of Earth-abundant elements with minimal toxicity, it is stable in ambient conditions, in water, and up to at least 500 C in air. It has strong optical absorption and has a suitable bandgap (1.8 – 1.9 eV) for tandem PV applications. In recent work, we showed that the bandgap can be tuned over the range 1.4 – 1.9 eV by chalcogen alloying, while remaining entirely within the perovskite phase [1, 2]. However, understanding of the electronic properties of chalcogenide perovskites – and the factors that may limit performance of future devices – remains elusive. Little has been reported on defect characterization, carrier mobility, mobility-limiting mechanisms, or dopability.<br/>In this work, we report electronic transport measurements and trends for epitaxial and polycrystalline BZS thin-films grown by physical vapor deposition. Hall effect measurements show <i>n</i>-type behavior as-grown, with carrier concentration and mobility correlated to synthesis parameters and structural properties measured by x-ray diffraction (XRD). Temperature-dependent Hall measurements show that mobility is primarily limited by phonon scattering at room temperature, with a transition to impurity-scattering at cryogenic temperatures. The carrier concentration can be tuned by post-growth annealing, nearly to intrinsic levels, and our results support the hypothesis that sulfur vacancies are the predominant shallow donors. As time allows, we will also present work exploring the doping limits, explored via <i>n</i>- and <i>p</i>-type ion implantation. Insights from this work will support future efforts towards PV device design, fabrication, and optimization.<br/><br/>[1] I. Sadeghi, <i>et al.</i>, <i>Expanding the Perovskite Periodic Table to Include Chalcogenide Alloys with Tunable Band Gap Spanning 1.5–1.9 eV</i>, Advanced Functional Materials <b>33</b>, 2304575 (2023).<br/>[2] K. Ye, et al., <i>A Processing Route to Chalcogenide Perovskites Alloys with Tunable Band Gap via Anion Exchange</i>, Advanced Functional Materials <b>n/a</b>, 2405135 (2024).