Doped semiconducting polymer nanoantennas for tunable organic plasmonics

Optical nanoantennas based on organic plasmonics are promising for their higher degree of tunability over metallic nanostructures. Here, nanodisks of polythiophene-based semiconducting polymers provide nanooptical antennas with resonances that are tunable over a 1000 nm wavelength range and can be switched off or on by doping modulation. Optical nanoantennas are often based on plasmonic resonances in metal nanostructures, but their dynamic tunability is limited due to the fixed permittivity of conventional metals. Recently, we introduced PEDOT-based conducting polymers as an alternative materials platform for dynamic plasmonics and metasurfaces. Here, we expand dynamic organic plasmonic systems to a wider class of doped polythiophene-based semiconducting polymers. We present nanodisks of PBTTT semiconducting polymer doped with a dicationic salt, enabling a high doping level of around 0.8 charges per monomer, and demonstrate that they can be used as nanooptical antennas via redox-tunable plasmonic resonances. The resonances arise from the polymer being optically metallic in its doped state and dielectric in its non-conducting undoped state. The plasmonic resonances are controllable over a 1000 nm wavelength range by changing the dimensions of the nanodisks. Furthermore, the optical response of the nanoantennas can be reversibly tuned by modulating the doping level of the polymer. Simulations corroborate the experimental results and reveal the possibility to also modulate the optical nearfield response of the nanoantennas.Funding Agencies|Knut and Alice Wallenberg Foundation; Swedish Research Council [2020-00287]; Swedish Foundation for Strategic Research (SSF); Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]