Room-Temperature Synthesis and Photodetector Performance of All-Inorganic Lead-Free Cs3Bi2X9 (X = Cl, Br, I) Perovskite Nanocrystals.

All-inorganic halide perovskites have gained significant interest as environmentally friendly alternatives to Pb-based perovskites for optoelectronic applications. Here, we report the preparation of Pb-free inorganic Cs3Bi2X9 (X = Br, I, Cl) perovskite using a simple room-temperature antisolvent recrystallization method on soda-lime glass substrates. We thoroughly analyzed and compared the structural, optical, and morphological properties of these films. X-ray diffraction analysis revealed that the Cs3Bi2Cl9 perovskite has the largest crystallite size (51 nm) compared to the Cs3Bi2Br9 and Cs3Bi2I9 perovskites. The perovskite films demonstrated enhanced crystallinity and exhibited hexagonal and orthorhombic phases with distinct space groups. Raman spectroscopy confirmed the successful formation of the Cs3Bi2X9 phase. Field emission scanning electron microscopy analysis showed that Cs3Bi2X9 exhibited irregular morphologies with noticeable voids across all samples. The surfaces were predominantly covered with uneven, spherical-like granules. The surface morphology displays dense packing with evident porosity and particle sizes ranging from submicrons to a few micrometers. The elemental analysis of the Cs3Bi2X9 perovskite revealed the formation of nearly stoichiometric films. The light absorption edge of Cs3Bi2X9 varied from 1.8 to 3.2 eV, depending on the halide composition. The formation of Cs3Bi2X9 perovskites was confirmed using X-ray photoelectron spectroscopy analysis. Finally, we fabricated photodetectors based on Cs3Bi2X9. Among these, the Cs3Bi2Cl9 perovskite-based photodetector exhibited superior performance, with a detectivity of 29.6 × 108 Jones, photoresponsivity of 1.14 mA/W, a fast rise time of 0.21 s, a decay time of 0.35 ms, and an internal quantum efficiency of 2.45 × 10-1 %. These findings demonstrate the potential of Cs3Bi2Cl9 perovskite-based photodetectors as promising candidates for next-generation, lead-free photodetector devices.