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 × 10^?4 cm² V^?1. Excitingly, the fabricated device based on 2D Cs₃Bi₂Br₉ nanoflakes demonstrates ultrahigh sensitivity of detecting X-ray (1.9 CGy_air^?1cm^?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.