Combined Purification and Crystal Growth of CsPbBr3 by Modified Zone Refining

Abstract

Semiconductor-based ionizing radiation detectors at room temperature have been widely applied in national security, medical imaging, and scientific research. Current commercially available detector materials such as cadmium zinc telluride (CdZnTe) and thallium bromide (TlBr) still suffer from some drawbacks, including structural defects and chemical instability. Therefore, researchers have continuously explored alternative high-performance and low-cost radiation detection materials. The all-inorganic semiconducting perovskite cesium lead bromide, CsPbBr3, exhibits promising properties for ionizing radiation detection applications and has attracted extensive research attention in recent decades.

To achieve the high purity required for semiconducting detector operations, conventional growth procedures for CsPbBr3 single crystals typically involved the separate purification of precursor materials. Purified PbBr2 and CsBr were subsequently combined in a new reaction vessel for synthesis and crystal growth. The novelty of this work is the development of a set of reliable protocols that can combine the purification and the crystal growth into a continuous process in a single reaction vessel via modified zone refining to achieve higher production efficiency. In this work, a series of CsPbBr3 samples with different growth histories were obtained through this protocol. Polycrystalline CsPbBr3 was first synthesized from the melt of binary compounds CsBr and PbBr2. Moisture and oxides in the synthesized CsPbBr3 compounds were removed by a reduction process under a flowing hydrogen stream. The CsPbBr3 materials were then purified and grown into high-quality single crystals via the modified zone refining process.

Obtained crystals were subjected to several characterizations such as powder X-ray diffraction analysis, trace impurity level determination and elemental composition identification. Moreover, photo-electrical properties of CsPbBr3 samples were evaluated through characteristic current-voltage (I-V) tests and photoresponse measurements. Obtained single crystals exhibited an electrical resistivity within a range of 10^8~10^9 Ω·cm, meeting the requirement of high resistivity for detector materials. Different samples displayed different photoresponse performances, which can be used to guide future crystal preparation to produce single crystals with a high signal-to-noise ratio (SNR) under the illumination of a light source.