Evaluation of a surface roughness-dependent trimodal switchable mirror using a dry deposition method

We used a nanoparticle deposition system (NPDS) to fabricate surface roughness-dependent trimodal switchable mirrors using a non-electrochromic antimony-doped tin oxide (ATO) film with dry-deposited micro- and nano-sized ATO particles. The devices switched among transparent, mirror and black states. Reversible Ag electrodeposition onto flat ITO glass and the rough surface of the ATO film obviated the need for an electrochromic material. NPDS creates very rough films by supersonically spraying powder onto a substrate. The roughness of the micro-sized ATO film was greater than that of the nano-sized ATO film. As both films were sufficiently rough, a completely black state could be achieved by both devices (0% transmittance over the entire visible wavelength), attributable to light scattering. In contrast, the electrochemical properties of devices with the micro-sized ATO film were superior to those of devices using the nano-sized ATO film because the greater roughness increased the active surface. The charge transfer resistance of devices with the micro-sized film (38 Ω) was lower than that of devices with the nano-sized film (44 Ω). The charge capacity of devices with the micro-sized film (109.87 mC/cm2) was much higher than that of devices with the nano-sized (95.59 mC/cm2). The cyclic transmittance of the device using the micro-sized ATO film was evaluated over 500 cycles with 0% diminution for its durability. Therefore, a trimodal switchable mirror was demonstrated by controlling the surface roughness of a non-electrochromic film.