This dissertation describes the author’s findings concerning the electrochromic (EC) thin films and devices during his PhD work. Besides the introductory (Chapter 1) and concluding (Chapter 6) chapters, four separate chapters (Chapters 2 to 5) are written as the main body of this dissertation. The first three chapters (Chapters 2 to 4) mainly deal with some universal principles and equations, simulated by the author, for three different configurations of electrochromic devices (ECDs). The last chapter (Chapters 5) addresses how the author simulated ion transport in an electrochromic thin-film. Since all of the ECDs discussed belong to the works for modeling and simulation, this dissertation is entitled “Modeling and Simulation for Electrochromic devices.” To present a clear picture of this dissertation, the main contents are summarized as follows. In the chapter 2, the diffusion model describing mass transport in a solution-type complementary electrochromic device containing heptyl viologen and N,N,N’,N’-tetramethyl-1,4-phenylenediamine is proposed and is solved using the finite element method. Using the method, a numerical solution to the transient concentration profile of the diffusing species is obtained for appropriate initial and boundary conditions during the coloring/bleaching process. Limiting coloring species are presented and are determined by the electrode at which the steady-state concentration profile is established faster. The simulated steady-state current density during coloring/bleaching fit well with the experimental data. In the chapter 3, this study uses computer simulations to investigate the effect of the active area of a complementary electrochromic device on switching response. The switching response curves of darkening and bleaching were simulated with an equivalent circuit model of a thin-film-type device. This study uses a tungsten oxide/Prussian blue complementary device as the simulated system, and demonstrates the steady-state response of the charge density within the device. Computer simulations were performed using the finite element method in the COMSOL Multiphysics® program. Numerical results provide some useful information for the development and application of electrochromic devices. Charge density dynamics reveal the kinetic behavior of charge transport. The graph of injected or extracted charge density versus characteristic lengths for various sizes shows an approximately linear relationship. The graph of switching times versus characteristic lengths also shows an approximately linear relationship. A larger active area produces a longer switching time. By changing the geometrical shape of the active area and the thermodynamic parameters of the two electrodes in electrochromic films, it is possible to analyze and predict the switching response and the optical performance of a thin-film type device. In the chapter 4, the electrochemistry of a Prussian blue (PB) thin film on an ITO electrode was studied in propylene carbonate (PC) solution using the Li+ of lithium perchlorate (LiClO4) electrolyte as the counter ion by cyclic voltammetry (CV). A model is proposed for the cyclic voltammetric behavior of a PB film on an ITO electrode surface. The model incorporates electron-transfer kinetics at film/ITO interface and diffusion within the film. The cyclic voltammetry of a heptyl viologen (HV(BF4)2) solution was also studied. The Butler-Volmer equation was used to describe the cyclic voltammogram of a HV solution on an ITO electrode surface. The cyclic voltammetric behavior of a complementary electrochromic device (ECD) based on a Prussian blue (PB) thin film and a heptyl viologen (HV(BF4)2) solution was studied by the combination of the CVs for the PB film and HV in PC containing 1M LiClO4. In the chapter 5, A new aromatic poly(amine-imide) electrochromic thin film synthesized with N,N-bis(4-aminophenyl)-N’,N’-diphenyl-1,4-phenylenediamine and 3,3’,4,4’-benzo-phenonetetra carboxylic dianhydride, abbreviated as poly(PD-BCD), was used for study of ion transport within thin film. The poly(PD-BCD) thin-film electrode has been characterized by cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM). Experimental data was analyzed by EQCM modeling and simulation. As the polymer chain acquires positive charge during the oxidation of poly(PD-BCD) to its radical cation state or dication state, the anions would insert into the polymer matrix in order to neutralize the charge. However, when the electrodes were cycled in electrolytes containing different cations, including 0.1 M LiClO4/ACN, 0.1 M NaClO4/ACN and 0.1 M TBAClO4/ACN, the experimental results revealed two mechanisms for the redox reaction. A plot of mass change (Δm) vs. accumulated charge (Q) gave a slope, from which the electrochromic mechanism can be extracted. The slopes of Δm-Q obtained from the CV-EQCM measurements in three electrolytes were different for the first redox stage, but the slopes were almost the same for the second redox stage. This means that, in addition to the involvement of anions, cations also play an important role in the first redox stage, however, the role of the cations is less in the second stage. Moreover, two reaction mechanisms for the two reaction stages of poly(PD-BCD) are proposed in this study.