Flexible All-Solid-State Electrically Tunable Photonic Crystals

Electrically tunable photonic crystals (ETPCs) are promising intelligent materials because of their precise and easy control, fast response time, and convenient implementation. However, the previously reported ETPCs require specific liquid cells that contain solvent, electrolytes, or liquid crystals. These features result in a long switching time, large hysteresis, long and complex fabrication process, and unstable operation with a short lifetime. Here, to address these issues, a new approach of ETPCs, that is, flexible all-solid-state ETPCs, is proposed through chemically induced polymer swelling and lattice control in photonic crystals using dielectric elastomer actuators (DEAs). The all-solid-state ETPCs show a wide range of color changes from red to bluegreen and long-term stable operation with low hysteresis. The DEA coated with transparent compliant electrodes stretches the chemically swollen colloidal crystal-polydimethylsiloxane composite (redshift) under an applied electric field; the swollen interlattice distance in the colloidal crystals decreases with the electrically induced stretching, causing a blueshift in the color. The conformable color change of the ETPCs on a 3D structure is successfully demonstrated owing to their unique flexibility by covering 3D surfaces with the developed ETPCs. The proposed flexible all-solid-state ETPCs are expected to be used as artificial camouflage skins in the future.