Silver Bismuth Iodide Nanomaterials as Lead-Free Perovskite for Visible Light Photodetection

The synthesis of silver bismuth iodide (SBI) nanocomposite thin films for visible light photodetection application is reported. The formation of different compositions of SBI (AgBiI₄ or Ag₂BiI₅) is achieved by varying the Ag precursor concentration in the solution. Heat treatment of the films at 125 °C for 15 min results in crystalline AgBiI₄ and Ag₂BiI₅ pin-hole free films and displays uniform coverage of the surface with densely packed grains. The grain sizes in the films are >100 nm for AgBiI₄ and >300 nm for Ag₂BiI₅. The direct optical band gaps are 1.63 and 1.66 eV for the AgBiI₄ and Ag₂BiI₅ films, respectively, making them suitable for light-harvesting applications. The fabricated films exhibit good photodetector responsivity and detectivity under 454 nm light illumination. At 1 V bias, the photoresponsivity of Ag₂BiI₅ films was 1.25 × 10⁵ A/W with specific detectivity of 3.8 × 10⁷ Jones. A photocurrent on/off ratio of approximately 39.6, a photoresponse rise time of 1.99 s, and a fall time of 2.04 s were also observed. The Ag₂BiI₅ perovskite films show better performance for photodetector applications than AgBiI₄ films.