K. A. Th. Thoma

Demixing profiles in oxides upon the application of an electrical field

Abstract A computer model incorporating Poisson’s equation, current density and charge continuity equations is used in order to study demixing phenomena in multicomponent oxides upon the application of an electrical field. In particular, results are presented for (Co,Mg)O and compared to experimental ones reported in the literature.

Transport processes in α-quartz through computer modeling

The charging and discharging processes in a-quartz sandwiched between two blocking contacts are studied by solving numerically the transport equations. Results for the transient current are in good agreement with experiment. The rotation of crystallographic planes upon the application of an electric field is also quantitatively justified through results of the spatial distribution of the electric field.

P-N junctions in semiconducting TiO2 studied through computer modelling

The dependence of the formation of a p-n or p-p+ junction in semiconducting TiO2 as a function of various parameters is investigated through a computer model. The effect of the polarizing conditions on the I–V characteristics is also discussed and related to experimental results.

Oxide thickness and roughness factor as parameters for TiO2-dye sensitized solar cells performance

Oxide surface roughness in connection to oxide thickness has proved to be a key parameter for the performance of a dye sensitised solar cell. In this work, the numerical simulation of the system TiO2-photo sensitive dye of a dye sensitized TiO2 solar cell focuses on these two parameters. The steady-state numerical model used is based on the continuity and transport equations for charge species involved in the system, in connection to Poisson’s equation. Light absorbance is set dependent upon TiO2 porosity and resulting electron density after illumination is derived as a function of the illuminating beam characteristics and material properties. Electron lifetime in the bulk is set dependent upon electron distribution with electron lifetime at the surface taking into consideration surface recombination. An effective dielectric constant dependent also upon the porosity of TiO2 is used in the model. Results for different values of the TiO2 thickness and surface roughness leading to optimum values for the cell performance are found in accordance with results reported in the literature.

Appearance of nonuniform electric fields in solid ionic conductors

A computer model is used to study charge transport in ionic materials upon the application of an electrochemical potential gradient. The model incorporates both the diffusion and drift mechanisms, permitting the evaluation of the contribution of each mechanism. Each mechanism is shown to be dominant depending on the material parameters and the experimental conditions. The results obtained are compatible with experimental and theoretical ones as reported in the literature, suggesting that in several cases studying the transport of mobile species in ionic materials upon the application of an electrochemical potential gradient, the existence of an internal field cannot be ignored.

The effect of local inhomogeneities on the performance of solid ionic devices

Application of voltages to mixed conductors can lead to the formation of local inhomogeneities. As a result, high local field values may appear with an impact on the device performance. The effect of voltage application is investigated through a computer model based on Maxwells third equation and fundamental equations governing charge transport. Results are in agreement with experimental ones reported in the literature. The formation of p-n junctions is also clearly demonstrated.

Transient response of fe doped TiO2 upon the application of a D.C. voltage

The time evolution of the spatial dependence of densities of mobile charged species in homogeneously iron doped rutile, originally p-type, upon the application of a dc voltage is given in comparison to the steady state results. The time variation of voltage distribution in the sample is also shown and the contribution, changing with time, of the various charged species in the resulting electric field is discussed.

A computer model for transport processes in solid electrolytes

A computer model based on the Poisson, current density and continuity equation, used to study transient and steady state phenomena in insulators and solid electrolytes with one type of mobile species, is extended to the case of materials with two types of mobile species. The derived distributions are compared for the two cases.

Selected parameters leading to an optimized DSSC performance

Dye Sensitized Solar Cells (DSSC), the third generation of photovoltaic devices, can be considered as most promising among renewable energy sources. Although DSSCs are devices very easy to fabricate, there is a large number of design parameters upon which their performance depends. In this review paper a lay out is given of the various parameters at which research groups focus aiming towards optimum performance of the DSSCs.

Problems and the progress made in modeling devices based on ionic materials

Computational simulation techniques have been extensively used to investigate physical phenomena in semiconductor devices with similar techniques utilized for the study of their competitors, ionic devices [1]. This paper is focusing on models based on the physics of carrier transport referring also shortly to equivalent circuit models, a much celebrated tool in the area of ionics.