Cyano‐Coordinated Tin Halide Perovskites for Wearable Health Monitoring and Weak Light Imaging

Abstract Low‐toxicity tin halide perovskites with excellent optoelectronic properties are promising candidates for photodetection. However, tin halide perovskite photodetectors have suffered from high dark current owing to uncontrollable Sn 2+ oxidation. Here, 2‐cyanoethan‐1‐aminium iodide (CNI) is introduced in CH(NH 2 ) 2 SnI 3 (FASnI 3 ) perovskite films to inhibit Sn 2+ oxidation by the strong coordination interaction between the cyano group (C≡N) and Sn 2+ . Consequently, FASnI 3 ‐CNI films exhibit reduced nonradiative recombination and lower trap density. The self‐powered photodetector based on FASnI 3 ‐CNI exhibits low dark current (1.04 × 10 −9 A cm −2 ), high detectivity (2.2 × 10 13 Jones at 785 nm), fast response speed (2.62 µs), and good stability. Mechanism studies show the increase in the activation energy required for thermal emission and generated carriers, leading to a lower dark current in the FASnI 3 ‐CNI photodetector. In addition, flexible photodetectors based on FASnI 3 ‐CNI, exhibiting high detectivity and fast response speed, are employed in wearable electronics to monitor the human heart rate under weak light and zero bias conditions. Finally, the FASnI 3 ‐CNI perovskite photodetectors are integrated with a 32 × 32 thin‐film transistor backplane, capable of ultraweak light (170 nW cm −2 ) real‐time imaging with high contrast, and zero power consumption, demonstrating the great potential for image sensor applications.