2D Cs₂AgBiBr₆ with Boosted Light–Matter Interaction for High‐Performance Photodetectors

Abstract Lead‐free double perovskite Cs₂AgBiBr₆ has attracted significant research interests for optoelectronic applications because of its nontoxicity, inherent stability, and high detection sensitivity. In this work, the 2D Cs₂AgBiBr₆ with a thickness of ≈5 nm and lateral length larger than 50 µm is successfully fabricated by a space‐confined method. The fabricated ultra‐thin 2D Cs₂AgBiBr₆ exhibits significant advantages on photodetection, due to its enhanced light–matter interaction. Remarkably, compared with bulk Cs₂AgBiBr₆, 2D Cs₂AgBiBr₆‐based photodetectors exhibit dramatically improved optoelectronic properties including ultra‐high detectivity (D^*) of 7.4 × 10¹⁴ Jones (more than ten times), photoresponsivity (R) of 54.6 A W⁻¹ (exceeding 4.7 times), an on/off ratio of 7.4 × 10⁴ (more than ten times), and a fast response time of ≈1.7 ms (exceeding 30 times). In addition, due to the strong photon recycling effect of Cs₂AgBiBr₆, optical properties in both light absorption and emission can be effectively engineered by the material thickness, which enables a tunable wavelength‐dependent photodetection. The results provide further insights on the light–matter interaction of environmentally friendly 2D perovskites related materials and shine light on their high‐performance optoelectrical applications.