Synthesis of Single Crystal Perovskite MAPbBr3 by Using Anti-solvent Vapor-assisted Crystallization Method for X-Ray Photodetector Application

Abstract

Perovskite methylammonium lead tri-bromide (MAPbBr3) has been extensively studied for active material of X-ray photodetector, due to its suitable bandgap with the X-ray energy range and its high value of charge carrier diffusion to produce both high efficiency and sensitivity of photodetector. However, the high resistivity due to the large crystal defect density caused by its polycrystalline crystal structure will reduce the charge carrier mobility and lifetime and therefore produce less sensitive photodetector. The solution to overcome these problems is the perovskite MAPbBr3 material must be in the form of single crystal to produce low crystal defect density. Another practical problem for X-ray photodetector application is the most of the reported perovskite crystals have the size less than 1 cm2. For the practical purposes of X-ray photodetector devices, a cubic structure and large crystal dimension (larger than 1 cm2) are required to adjust into the flat-panel detector. In this research, MAPbBr3 perovskite crystals were synthesized by using Anti-solvent Vapor-assisted Crystallization (AVC) method. The precursor MAPbBr3 was prepared by dissolving MABr and PbBr2 with molar ratio of 1.25 and 1.0 in dimethylformamide (DMF). Dichloromethane (DCM) was used as anti-solvent. The diffusion of anti-solvent DCM into precursor solution was controlled by providing a small hole on the top of vial which contains the precursor. The crystal growth rate was controlled by varying the volume ratio of DCM and MAPbBr3 precursor solution. The obtained largest crystal size of 7mm × 7mm was prepared with a volume ratio of DCM and precursor of 2.67 and a volume of 3 mL precursor solution. The energy gap MAPbBr3 crystal is 2.14 eV derived from UV-Vis absorbance spectrum. The XRD pattern of the crystal showed that the perovskite MAPbBr3 had cubic crystal structure with a lattice constant of 5.99 Å. The diffraction pattern of the crystal showed a dominant peak of crystal plane (100). This result confirmed that the synthesized MAPbBr3 crystal has a single crystal oriented in x-axis direction.