Active Metasurface Thermal Emitters by Metallic Polymers

Conducting polymers (CPs) have been a versatile and effective material for dynamically controlling optical properties with applications ranging from electrochromic windows and displays to variable infrared (IR) emittance devices and terahertz modulators. In particular, its biocompatibility, flexibility, reversibility, solution-processability, and non-volatile switching make it suitable for radiative thermoregulation under various application scenarios. However, the current CPs for variable thermal emittance devices largely have low conductivity and are limited to thin film configuration, resulting suboptimal emissivity tunability. Here, we numerically and experimentally demonstrate CPs with extraordinary optical conductivity and properly designed metasurface structure can outperform the conventional counterparts. The IR emissivity tunability is achieved by synthesizing solution-processable polyaniline doped with camphor sulfonic acid (PANI-CSA) and characterizing the complex refractive indices at its conducting and insulating state. A forward-designed broadband wide-angle metasurface emitter based on asymmetric Fabry-Pérot cavity and gap surface plasmon resonance effectively utilizes the lossy dielectric properties at its insulating state for the high-emissivity mode. When switched to the conducting state, the metasurface becomes highly metallic and reflective, resulting in the low-emissivity mode. This study marks a new approach as we perform the co-design of macromolecular and photonic structure to enable solution-processable active metasurfaces.