Silver Ions Assisted Inversion Temperature Crystallization of 2D Cs₃Bi₂Br₉ Nanoflakes for Highly Sensitive X-Ray Detection

2D perovskites have attracted wide attention for optoelectronic applications because of their unique layer structure and tunable outstanding optical/electrical properties. In addition, 2D Cs3Bi2Br9 nanoflakes possess large effective atomic number, high resistivity, high density as well as excellent stability, rendering it a promising material for X-ray detection. Nevertheless, it is full of challenges to synthesize 2D Cs3Bi2Br9 nanoflakes by conventional inversion temperature crystallization (ITC) strategy due to the existence of Br- vacancies in the Cs3Bi2Br9 crystal nucleus. Herein, an Ag+ assisted ITC (SAITC) strategy to grow 2D Cs3Bi2Br9 nanoflakes is proposed. The synthesis mechanism revealed by both experiments and theoretical calculations can be mainly ascribed to the passivated Br- vacancies and enhanced structure stability by adding Ag+ which can effectively prevent the oxidation of 2D Cs3Bi2Br9 nanoflakes from growth of hybrid crystals. The synthesized high-crystallinity 2D Cs3Bi2Br9 nanoflakes possess direct bandgap characteristic, and the mobility lifetime can reach 9.8 x 10(-4) cm(2) V-1. Excitingly, the fabricated device based on 2D Cs3Bi2Br9 nanoflakes demonstrates ultrahigh sensitivity of detecting X-ray (1.9 CGy(air)(-1)cm(-2)) at very low driven voltage (0.5 V) due to the photoconductive gain mechanism. The 2D Cs3Bi2Br9 nanoflakes synthesized by SAITC method have great potential for developing highly sensitive optoelectronic devices.