Dissertação para obtenção do Grau de Doutor em
QuímicaThis Ph.D. project is focused on the synthesis of functional inorganic materials, their formulation into inks and their deposition using inkjet printing on non-conventional substrates, such as paper, with the ultimate goal of advancing the state-of-the-art in the area of printed electrochromic displays. Other materials, inks,techniques and substrates were also explored.
The first step in building a printed electrochromic display is to synthesize the functional materials necessary for the different layers of the device; this part of the work focused on inorganic electrochromic
materials (tungsten oxide and vanadium oxide) and on transparent conductive oxides (TCO). ATO(antimony tin oxide) was synthesized using the Pechini method and the results obtained were promising.
Tungsten oxide and vanadium oxide nanoparticles were also synthesized via a sol-gel route. FTIR,Raman and X-ray diffraction spectroscopic measurements showed that tungsten oxide nanoparticles
synthesized via sol-gel are mainly in an amorphous state, with hexagonal crystalline domains, and allowed the analysis of the hydration extent of those nanoparticles. Vanadium oxide gel synthesized in this
work is similar to those previously described in the literature, consisting of V2O5.6H2O, with microstructures similar to orthorhombic V2O5, while Raman spectroscopy also showed the presence of amorphous domains. The nanoparticle sizes were measured combining Dynamic Light Scattering,
sedimentation and microscopic techniques (AFM and TEM). Tungsten oxide particles presented an average nanoparticle size between 160 and 200 nm, and vanadium oxide of 60 nm.
The nanoparticles were used to produce ink formulations for application in inkjet printing. In addition to tungsten oxide and vanadium oxide, other electrochromic materials were printed. This part of the work
examined the possibility of inkjet printing several organic (poly(thiophene)s) and inorganic electrochromic materials (metal oxides and metal hexacyanometallates) and also evaluated the performance of the
resulting electrochromic devices. Poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate), poly(3-hexylthiophene), tungsten oxide, vanadium oxide and Prussian blue were inkjet printed on flexible substrates, such as plastic and paper.
Solid-state electrochromic devices were assembled at room temperature on plastic and on paper substrates, without sintering the printed films, showing, in some cases, excellent contrast between the on and off state. The tungsten oxide and vanadium oxide devices were then tested through
spectroelectrochemistry by Visible/NIR absorption spectroscopy. Tungsten oxide showed a dual spectroscopic response depending on the applied voltage and vanadium oxide presented several redox
steps, which give rise to a variety of color transitions, also as a function of the applied voltage. Color space analysis was used to characterize the electrochromic transitions; monitorization of the color contrast and cycling tests, as well as techniques such as cyclic voltammetry, were also used to characterize device performance
