A semi-empirical analysis of dye adsorption and electron transport in dye sensitized solar cells (DSSCs)

Abstract

In order to provide a comprehensive understanding of dye adsorption parameters and their relation with the structural and transport properties of dye sensitized solar cells (DSSCs), a combination of experiments and modeling of the dye adsorption and electron transport characteristics with respect to the photoanode thickness was performed. The obtained experimental data include scanning electron microscopy (SEM) images, UV-Vis data, steady state current–voltage (J–V) characteristics and open circuit voltage decay (OCVD) data. By monitoring the time evolution of the bulk dye solution and applying the fitting model, the dye loading is reproduced to determine the adsorption parameters, such as the optimum time and amount of dye loading. Additionally, the photoabsorption coefficient of the DSSCs for various active layer thicknesses was determined. In addition, the presented analysis approach builds up a relation between the dye adsorption dynamics and the structure of the nanoparticle matrix to estimate the aggregation parameters. The current–voltage characteristics are investigated for different photoanode thicknesses and the optimum thickness is determined. The discussion also highlights the importance of the localized state distribution in electron transport analysis regarding the active layer thickness by building up an analytical formalism for the OCVD, lifetime, diffusion length and nonlinearity recombination parameter (β). It is found that considering a constant or variable β can provide fundamental interpretations for recombination pathways. The proposed integrated strategy can provide a powerful tool to study the microscopic processes and parameters governing dye-sensitized solar cell (DSSC) behavior. The presented methodology is especially applicable for the investigation of photoanodes with different morphological features such as nanotubes or nanorods, as well as different sensitizers.