Light-Responsive Cu–BFO/PVDF-HFP Bilayer Films for Micromanipulation and Soft Robotic Applications

Abstract A light-driven heterostructure was developed by depositing a Copper-doped Bismuth Ferrite (Cu–BFO) thin film onto a flexible poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) substrate. Unlike conventional photoactuators governed primarily by photothermal expansion, this bimorph demonstrates a fully reversible bending consistent with a photostriction-dominated response. Kinetic decoupling and isothermal analysis at a fixed thermal threshold of 35 °C explicitly reveal a severe performance divergence: under 405 nm violet illumination, the actuator triggers an instantaneous mechanical deflection reaching an average maximum bending angle of 79.9° ± 0.7°, whereas 532 nm green and 635 nm red light yield near-zero, baseline thermal responses (2.8° ± 0.3° and 5.7° ± 0.9°, respectively). This strict wavelength selectivity, with significant response occurring only above the Cu–BFO bandgap, strongly supports the actuation predominantly photostrictive mechanism. The resulting internal electric field induces lattice strain through the converse piezoelectric effect, providing a highly efficient light-to-mechanical energy conversion pathway. Finally, a light-controlled microgripper capable of lifting objects weighing 1.9 mg with a payload-to-weight ratio of 1.58, demonstrates the practical potential of this heterostructure for remotely powered soft robotic and haptic applications.