Purification and Improved Photoelectric Properties of Lead-Free Perovskite Cs₃Bi₂Br₉ Crystals

The lead-free halide perovskite Cs3Bi2Br9 is a promising semiconductor material for room-temperature X-ray detection due to its excellent properties. However, material purity and crystal quality still limit the use of Cs3Bi2Br9 crystals as detectors. In this work, we present a highly efficient purification method using continuous vacuum extraction to sublimate BiBr3 precursors for Cs3Bi2Br9. Impurity analysis via inductively coupled plasma mass spectroscopy showed that the purification method successfully removed most of the impurities in BiBr3 precursors and improved the purity by at least one order of magnitude. Centimeter-sized Cs3Bi2Br9 single crystals were grown by the vertical Bridgman method. The improved properties after purification were confirmed by UV-Vis-NIR spectra, infrared transmittance, and current-voltage (I-V) measurements. The results showed that the average transmittance of Cs3Bi2Br9 crystals significantly increased from 62% to 75% in the 0.5-20 & mu;m spectral range. Additionally, the resistivity increased by nearly three orders of magnitude from 5.0 x 10(9) & omega;& BULL;cm to 2.2 x 10(12) & omega;& BULL;cm, meaning the material will have low leakage currents and be suitable for developing applications for room temperature radiation detection.