Question

Refractive index and scattering of porous TiO2 films

Answer 1

Porous titanium dioxide (TiO2) films are essential components of dye sensitized solar cells (DSSCs) as well as perovskite solar cells (PSCs). Unfortunately, porosity, refractive index, and scattering properties of these films are only roughly known. This induces uncertainties in modelling and understanding of these solar cells. Since the literature provides only descriptions of the optical properties of the porous TiO2 layers with unclear relevance to these solar cells, we investigate porous TiO2 films really used in DSSCs and potentially usable in PSCs. The effective refractive index and the film porosity for different nanostructures that were fabricated from solution-based techniques were determined. The found values are 1.7982 ± 0.005 for the effective refractive index of one kind of TiO2 films and 1.62 ± 0.002 for another one. These values lead to porosities of 53.5% and 65%, respectively. The scattering of the films can be described by a wavelength-independent effective scattering parameter for one film type and by effective scattering particles with a diameter of 46.5 nm for the other film type. The determined porosities are also of relevance for the ionic transport which is functionally crucial in DSSCs and a disturbance in PSCs.