University of California, Riverside,
Keywords: electro-optical, electrochromic, carbon nanotubes, graphene, ionic liquid
Summary:Optical properties of electrochromic materials can be controlled by application of electric field allowing recent development of new applications such as smart windows technology for climate control and energy conservation in the buildings. Here we report the fabrication of a single-walled carbon nanotube (SWNT) thin film based electro-optical modulator in which the active electrochromic layer is made of a film of semiconducting SWNTs and the counter-electrode is composed of a film of metallic SWNTs with an ionic liquid utilized as electrolyte. We show that optimization of such electro-optical cells allowed a 100-fold increase in the operation speed with a significant amplitude of modulation of infrared transmittance maintained up to frequencies between 100 to 1000 Hz. The efficient electro-optical modulation is a result of the high porosity and high surface area of SWNT thin films which allow fast penetration of the ions and the formation of a 3-dimensional electric double layer capacitor involving the full thickness of the SWNT layer. The development of fast electrochromic systems provides an opportunity to expand the field of thin film SWNT optoelectronics into smart window applications, infrared modulators and shutters, and infrared imaging systems.