• Energy Research

This experimental work reports the activities of design, fabrication and characterization of an innovative solid-state electrochromic device, deposited on a single substrate with high transparency in the bleached conditions and a wide modulation of transmittance (?T of 60% at 750 nm) both in the visible and near-infrared wavelengths. A tailored formulation of the solid electrolytes, based on sulfonated tetrafluoroethylene-based fluoropolymer-copolymer dispersions and the accurate design of a suitable layer of porous tin oxide nanoparticles provided high coloration and bleaching kinetics and recovery of the pristine conditions, even after 500 complete cycles. Devices were scaled-up to 10 × 10 cm size, without mechanical and aesthetic defects and relevant homogeneity, throughout the coloration and bleaching processes. Furthermore, this device shows the further feature to be a low-emissivity dynamic solar control film, highly compatible with integration within insulated glazed units.

Hybrid electrochromic (EC) devices present an interesting configuration in which the advantage of both solid-state and liquid-based devices can be combined in order to optimize the device performances. In this configuration, a solid-state EC material is combined with a redox couple dissolved in the electrolyte. The redox electrolyte offers an unlimited charge capacity, thus allowing to fully exploit the electrochromic properties of the EC material. Here, we present a thiolate/disulphide (T/T) redox couple as a new redox shuttle for EC devices. In order to transfer the advantages of the redox couple to a solid state device, it was combined with a fully transparent thermally curable vinyl-acetate polymer. The obtained EC device was compared with that based on I/I showing higher transparency in the visible region of the solar spectrum and higher coloration efficiency. Most interestingly, the device based on T/T shows a slower self-bleaching process and it only loses 30% of its coloration after 1 h at open circuit. Such characteristic represents a great advantage for smart windows applications since it is not necessary to apply potential to maintain the device coloration, thus allowing a great energy saving.

Abstract We present a large area trifunctional glass prototype combining a photo-electrochromic (PEC) device and an organic light-emitting diode (OLED), interfaced through a properly designed electronic control system. A 12×17 cm2 PEC glass-on-glass module was realized, containing four dyesensitized solar cells (DSSCs) and a central electrochromic (EC) section deposited on the same glass panel. All PEC layers are screen-printed, including the mesoporous electrochromic layer, obtained from a custommade tungsten paste. DSSCs show an efficiency of 2.4%, while the coloration efficiency of the EC section reaches a value of 40 cm2C−1 at 700 nm. A 10×8 cm2 transparent white OLED was also realized, designed and tailored in order to unbalance the emission of light, i.e. maximizing the bottom emission. The efficiency of large area OLED section reaches 8 cd A-1 in the operative conditions and without light outcoupling enhancement systems. The OLED device is clamped on the back of the PEC module and all sections are electrically connected to an external electronic control system. The energy collected by the DSSCs is stored in supercapacitors and used when requested, either applied to the EC section to produce a light shading effect in the daytime, or to the OLED for illumination at night.

Solid-state ionic conductors embodying either protons or lithium ions are very attractive for large-area electrochromic (EC) devices. In this work, aiming at the preparation of a gel polymer electrolyte (GPE), two cheaper and non-toxic commercial resins are used: a urethane-based prepolymer (NOA65) and a vinyl acetate-based resin (MASTIFLEX). They are employed as host matrices to trap the liquid constituents, made of lithium perchlorate-propylene carbonate (LiClO-PC). Thermogravimetric analyses indicate that both resins show excellent thermal performance. Several GPE formulations are investigated with respect to electrical and optical properties, varying the polymer-to-liquid ratio and LiClO concentration. The EC devices made with the two GPEs are also characterized in terms of optical contrast, switching kinetics and repetitive switching cycles. These activities made it possible to find the best formulations finally employed for the fabrication of 100 cm large area EC devices. The obtained results demonstrate that low-cost GPEs based on commercial polymers are electrochemically stable as ion-conducting media for EC devices.