Investigation On Electrochromic Performance Of Oxide Thin Films For Electrochomic Devices

The thesis is focused on the electrochromic?EC?performance of oxide thin films for EC devices.The nanocrystal-in-glass tungsten oxide?WO₃?thin films with a nanoporous structural characteristic and the layered vanadium pentoxide?V₂O₅?thin films with nanocrystals embedded amorphous matrix were fabricated/synthesized.The EC performance of these nanocrytal-in-glass oxide thin films is investigated in organic and aqueous electrolytes with various conduction ions such as H⁺,Li⁺,Na⁺,Mg²⁺,and Al³⁺.Introducing various barrier layers?SnO₂,PEDOT:PSS and Al₂O₃?into the interface between the WO₃ thin film and electrolyte and their effect on the EC performance of the WO₃ thin films are also investigated.The WO₃-NiO complementary ECDs based on lithium ion liquid electrolyte were constructed.The simply structured ECDs with the Li⁺-PAM/WO₃/ITO configuration were assembled based on the free-standing quasi-solid lithium ion-contained polyacrylamide hydrogel.The main conclusions in the thesis are summarized as follows:1.The nanocrytal-in-glass WO₃ thin films were deposited at different substrate temperatures by the electron beam evaporation method.A high performance of the nanopore-involved WO₃ thin films is obtained.In particular,a high optical modulation??T?of 92%,91%and 87%,a coloration efficiency of 61.78,62.04 and67.59 cm² C^-1,and a large diffusion coefficient of 9.4×10^-10,7.79×10^-1111 and 5.92×10^-11cm² s^-1 in 0.1 M PC-LiClO₄,PC-NaClO₄,and PC-Al?ClO₄?₃ organic electrolytes were observed,respectively.The nanoporous structures could provide a free channel for the conduction ions and shorten cation ion diffusion distance.In addition,the nanocrystal embedded amorphous phase had a buffering effect,in favor of accommodating the volume change induced by the ion insertion/extraction.On the other hand,the uniform distribution of the amorphous and nanocrystal would help to reduce stress concentration and hence suppress structural collapse caused by local stress.The monovalent Li⁺with small radius exhibited a fast kinetics response.Accordingly,Na⁺and Al³⁺had a relatively slower kinetics response due to the bigger radius and stronger Coulomb force,respectively.In detail,Al³⁺,presenting a shallow diffusion depth in the electrode near-surface region,could stabilize the host framework owing to the strong electrostatic forces of the multivalent ions,leading to a reversible extraction of foreign ions from a host lattice.The nanocrystal-in-glass WO₃ thin films possessed a fast and reversible pseudocapacitive characteristic in Li⁺,Na⁺and Al³⁺electrolytes.The individual contributions from surface-or diffusion-controlled process were quantitatively analyzed as well.A higher interfacial resistance of the nanocrystal-in-glass WO₃ thin films was observed in trivalent Al³⁺electrolytes than that in monovalent Li⁺and Na⁺electrolytes by electrochemical impedance spectra?EIS?analysis.Besides,a low real capacitance and response frequency were obtained in Na⁺electrolytes.2.Introducing the SnO₂ barrier layer into the conduction ions-WO₃ system could enhance the ion diffusion and reduce the resistance of the active interface between electrolyte and electrode.The diffusion coefficient of the SnO₂/WO₃ stacked thin films was 2.59×10^-8,2.34×10^-8 and 9×10^-10 cm² s^-1 in Li⁺,Na⁺and Al³⁺electrolytes,respectively,in which the optical switching reversibility was greatly improved in the Na⁺-WO₃ system.Also,the effect of PEDOT:PSS and Al₂O₃ as interfacial barrier layers on the EC performance of the WO₃ thin films was investigated.3.The Electrochemically deposited V₂O₅:Mo thin films possessed a high EC performance due to a layered characteristic,which provides a free channel for the penetration of Na⁺and Mg²⁺with bigger radius than Li⁺.For instance,a high optical modulation??T?of 73%was exhibited in Na⁺electrolytes.4.The ITO/NiO/Li⁺electrolyte/WO₃/ITO complementary ECDs based on lithium ion liquid electrolyte could be switched from blue to transparent with a high coloration efficiency of 63.76 cm² C^-1.The optical switching reversibility stability of ECDs was enhanced by introducing the SnO₂ interfacial barrier layer.The free-standing polyacrylamide hydrogel containing lithium ions?Li⁺-PAM?had a good mechanical ductility of 300%stretching strain and a high electrial conductivity of2.14×10^-3 S cm^-1.The simply structured ECDs with the tri-layer Li⁺-PAM/WO₃/ITO configuration exhibited a high optical modulation of 89%at the applied voltages of-0.6/+1.4 V,in which the free-standing quasi-solid lithium ions-contained polyacrylamide hydrogel was used as the counter electrode,ion storage layer and conductive electrode.