Light-driven actuators that directly convert light into mechanical work have attracted significant attention due to their wireless advantage and ability to be easily controlled. However, a fundamental impediment to their application is that the continuous motion of light-driven flexible actuators usually requires a periodically switching light source or the coordination of other additional hardware. Here, for the first time, continuous flapping-wing motion under sunlight is realized through the utilization of a simple nanocrystalline metal polymer bilayer structure without the coordination of additional hardware. The light-driven performance can be controlled by adjusting the grain size of the upper nanocrystalline metallic layer or selecting metals with different thermodynamic parameters. The achieved highest frequency of flapping-wing motion is 4.49 Hz, which exceeds the frequency of real butterfly wings, thus informing the further development of sunlight-driven bionic flying animal robotics without external energy consumption. The flapping-wing motion has been used to realize a light-driven whirligig, a light-driven sailboat, and photoelectric energy harvesting. Furthermore, the flexible bilayer actuator features the ability to be driven by light and electricity, low-power actuation, a large deflection, fast actuation speed, long-time stability, strong design ability, and large-area facile fabrication. The bilayer film considered herein represents a simple, general, and effective strategy for preparing photoelectric-driven flexible actuators with target performances and informs the standardization and industrial application of flexible actuators in the future.
Keywords: bilayer film; continuous flapping-wing motion; flexible actuators; nanocrystalline metallic film; sunlight-driven.