Development of photoelectrochromic devices for dynamic solar control in buildings

Abstract

An experimental study of photoelectrochromic (PEC) devices for dynamic solar control in buildings is presented. The fabricated devices consist of a 400 nm thick WO 3 film, a 300 nm thick dye-sensitized nano-structured TiO 2 layer, a 0.5 M LiI/PC electrolyte and an electrodeposited Pt counter electrode. All layers were developed aiming to increase the device transparency without reducing its functionality. The PEC devices thus prepared exhibit fast coloration (∼12 min) under sunlight, considerable transmittance modulation ( T lum varying from 50% to 14% and contrast ratio of 3.6:1) and a haze factor in the bleached state equal to 27.8%. They can withstand more than 100 continuous coloration–bleaching cycles. Distinct differences were observed between PEC devices and electrochromics, regarding the change in color coordinates during coloration. The former take a green color as opposed to the deep blue color of the latter. Furthermore, in PEC devices the optical interference between the WO 3 and TiO 2 films can be used advantageously to tailor their color. A novel efficiency index, suitable for PEC devices, termed “photocoloration efficiency, PhCE” was introduced and it was used for their characterization. It was found that the PEC devices presented in this work have high photocoloration efficiencies during the initial coloration stages (∼6 min) and that they compare well in terms of PhCE with similar devices developed by others.