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

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.