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

Abstract 2D perovskites have attracted wide attention for optoelectronic applications because of their unique layer structure and tunable outstanding optical/electrical properties. In addition, 2D Cs 3 Bi 2 Br 9 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 Cs 3 Bi 2 Br 9 nanoflakes by conventional inversion temperature crystallization (ITC) strategy due to the existence of Br ‐ vacancies in the Cs 3 Bi 2 Br 9 crystal nucleus. Herein, an Ag + assisted ITC (SAITC) strategy to grow 2D Cs 3 Bi 2 Br 9 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 Cs 3 Bi 2 Br 9 nanoflakes from growth of hybrid crystals. The synthesized high‐crystallinity 2D Cs 3 Bi 2 Br 9 nanoflakes possess direct bandgap characteristic, and the mobility lifetime can reach 9.8 × 10 −4 cm 2 V −1 . Excitingly, the fabricated device based on 2D Cs 3 Bi 2 Br 9 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 Cs 3 Bi 2 Br 9 nanoflakes synthesized by SAITC method have great potential for developing highly sensitive optoelectronic devices.