Modeling of adsorption isotherms of dye N719 on titanium oxide using the grand canonical ensemble in statistical physics for dye sensitized solar cells

The physio chemical parameters involved in the adsorption process have been deduced directly from experimental adsorption isotherms by numerical simulation. We will introduce six main parameters to describe the adsorption process, namely; two densities of dye receptor sites Nm1 and Nm2, the numbers of absorbed molecules per site n1 and n2, the concentrations at half saturation C1 and C2. In order to investigate the type of interaction between the dye molecule and titanium dioxide, we calculate the adsorption energies of the dye molecule using our statistical physics model and the known Dubinin-Radushkevich model for comparison. The numerical values of adsorption process energy (Ea) indicated a chemical adsorption allowing a strong bound to avoid a dye desorption which is very useful to keep a DSSCs in good working order. We apply then our model to deduce thermodynamic functions which govern the adsorption mechanism such as internal energy, entropy and free enthalpy.