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 Sn²⁺ oxidation. Here, 2-cyanoethan-1-aminium iodide (CNI) is introduced in CH(NH₂)₂SnI₃ (FASnI₃) perovskite films to inhibit Sn²⁺ oxidation by the strong coordination interaction between the cyano group (C≡N) and Sn²⁺. Consequently, FASnI₃-CNI films exhibit reduced nonradiative recombination and lower trap density. The self-powered photodetector based on FASnI₃-CNI exhibits low dark current (1.04 × 10^-9 A cm^-2), high detectivity (2.2 × 10¹³ 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 FASnI₃-CNI photodetector. In addition, flexible photodetectors based on FASnI₃-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 FASnI₃-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.