A High-Performing, Visible-Light-Driven Actuating Material Responsive to Ultralow Light Intensities

Light-driven actuating materials are highly desirable for miniaturized, untethered devices and microrobots. However, current light actuators require high light intensity or the use of UV or IR light to operate, which greatly increase the cost and difficulty for real-life applications. Here, a significant visible (vis)-light-driven actuation effect in cobalt oxides/hydroxides (C–O–H), inducible at low intensities from ≈3 mW cm⁻² (≈0.03 sun), is reported. In the form of bilayered films, the actuators can curl into loops at 70–180 ms per loop, corresponding to a high intrinsic strain of more than 1% at strain rate 0.6% s⁻¹, and actuating stress exceeding 60 MPa, at ≈50 mW cm⁻² (≈0.5 sun). Linear actuators made from actuating hinges of C–O–H can weightlift objects ≈200 times heavier than the active material. A chemo-mechanics model describes the actuation well, showing that the mechanism is light-induced volume shrinkage assisted by diffusion, and C–O–H exhibits outperforming chemical driving force per unit light-intensity stimulation.