Electrical and optical investigations lead-free Cesium Bismuth iodide single crystal

Abstract

Extensive research efforts are currently focused on lead-free all-inorganic perovskite single crystals (SCs) due to their lower biological toxicity and improved material stability. These advancements address two significant obstacles in the implementation of practical device applications. Positive photoconductivity (PPC) under light illumination has been observed in lead-halide perovskite SCs. Given the optical activity of lead-free perovskites, it is anticipated that they will exhibit comparable characteristics. Nevertheless, we present in this study the discovery of negative photoconductivity (NPC) induced by light, coupled with a slow recovery method, in lead-free Cs3Bi2I9 perovskite material, which was successfully synthesized through the novel top-seed solution (TSS) process. In-depth investigations using femtosecond transient reflectance (fs-TR) spectroscopy demonstrate that these unique electronic transport characteristics originate from the generation of light-triggered trap states that are metastable within the perovskite crystal lattice. We computed the performance metrics of Cs3Bi2I9 SC detectors, encompassing detectivity (1.68 × 1012 Jones), responsivity (32 mA/W), and the current ratio (∼10257). The distinctiveness of these findings lies in the unique behavior of Cs3Bi2I9 SCs, which, despite being optically active, exhibit retroactive photocurrent upon irradiation. This behavior has rarely been observed in other lead-free perovskite materials.