Comparative study of mixed metal cation lead-free perovskites for visible light photodetection

Integrating materials of different functionalities and properties is a versatile approach towards realizing new hybrid functionalities in advanced optoelectronic devices. A general solution synthetic approach was performed to prepare three lead-free perovskite structures, caesium bismuth iodide (Cs3Bi2I9), methylammonium bismuth iodide (MA3Bi2I9) and a mixed metal cation perovskite structure (Cs1.5MA1.5Bi2I9). The material property investigations reveal the hexagonal crystalline phase with consistently grown micron sized crystals. The fully inorganic and hybrid lead-free perovskites were then configured in photodetector geometries by a simple spin coating method. The visible light self-powered photodetection was successfully demonstrated using the three different perovskites. Specifically, the photoelectrical analysis reveals that the assembled microcrystals of the perovskiteswere very sensitive towards visible light based on theiroptical bandgapsranging from 2.10-2.18 eVthat enables aphotosensitivity of (1.94-8.51)×102 at zero bias conditions. The responsivity and specific detectivity of the devices were estimated to be within (0.013-3.1)µA/W and (0.10-2.03)×109 Jones, respectively. On comparing the photodetector results, Cs3Bi2I9 show the highest performance than MA3Bi2I9 and Cs1.5MA1.5Bi2I9. However, the Cs1.5MA1.5Bi2I9 perovskite presents comparable device performances. These results highlight the promising potential of mixed metal cation perovskite films in the development of solution and ambient condition processed optoelectronic devices without complicating the structure with the addition of dopants or anti-solvents.