Fabrication and characterization of laser patterned electrochromic layer by layer thin film devices

The laser modified layer by layer (LmLBL) assembly technique can be used to fabricate 3-dimensional polymer structures. This technique uses the well-known layer by layer approach of repeated dipping of a substrate in alternating charged solutions. Additionally, during part of the dipping process laser light is incident on the sample creating locations with thinner layers. As an example of the potential of this approach, laser patterned thin films were fabricated using PAH and the electrochromic polymer PTEBS on ITO substrates. Multiple passes of laser light with different average laser powers during the PAH dipping phase result in several lined structures with different thicknesses, as measured with surface profilometry. Using a 450 nm semiconductor laser with 10mW of average power, PAH/PTEBS films with an overall thickness of 200 nm, leads to a reduction in thickness of roughly 20 nm. Quasi-solid-state devices are made using LmLBL films of PAH/PTEBS, a conducting gel, and a second PAH/PTEBS thin film. These devices switch from orange to green with an applied voltage of around 1.7V. The electrochromic switching times and optical contrasts are investigated in laser patterned devices as a function of average laser power used and the local thickness. Laser patterned areas show reduced optical contrast and altered switching times compared to non-patterned areas.