Reflective structural colors and their actuation using electroactive conducting polymers

Sammanfattning: The integration of inorganic photonic nanostructures with organic materials opens new possibilities to dynamically modify the optical response of photonic devices. This thesis focuses on how to generate efficient reflective structural colors and tune them in combination with a conducting polymer (CP). The main technological interest lies in color reflective displays, devices with ultralow power consumption that work with reflected environmental light. The main challenge is to obtain dynamic color tunability while maintaining good chromaticity and brightness. We first studied how to make efficient reflective structural colors and focused on highly reflective optical nanocavities based on metal-insulator-metal (MIM), combining the Fabry-Pérot effect and a broadband absorber. We demonstrated a full color palette by changing the spacer thickness and proposed different configurations to improve the chromaticity and reproduce black. We also explored subtractive coloration with a cyan-yellow-magenta (CYM) system to increase the relative luminance for reflective displays. We covered the CYM spectrum by combining plasmonic nanodisks with optical nanocavities, using a scalable nanofabrication method based on colloidal lithography. Subsequently, we modified our optical nanocavities by replacing the dielectric spacer with a low bandgap electroactive CP, polythieno[3,4 b]thiophene(pT34bT), to obtain active color tunability. By integrating the optical nanocavities in an electrochemical cell, we proved tunability of the reflected color across all the visible spectrum with low operating voltages and similar reflectance values for all the oxidation states. Those cavities can be considered a proof of principle for the development of tunable monopixels.  In addition, we explored vapour phase polymerization (VPP) as an alternative deposition method with direct patterning possibilities by UV-exposure of the precursor oxidant film. We developed optical reflective nanocavities with a spacer based on poly[3,4-ethylenedioxythiophene]:Tosylate (PEDOT:Tos) on metal mirrors, generating color images by different UV exposures. We showed the feasibility of generating images by using a UV photomask with different contrasts. Those cavities could also be switched in color by electrochemical tuning in an electrolyte, reaching different electrochromic states. This method has the potential to be extended to other types of polymers and to be used for display technologies.