Periodic structures

An alternative to the use of disordered structures to enhance diffuse light scattering is the introduction of porous materials in which a periodic variation of the refractive index has been built up. As it will be shown next, periodic structures allows to achieve high reflectance within the cell at targeted and well-defined wavelength ranges, which may prevent the drawback of the loss of transparency. Also, in some cases, highly reflecting structures can be only a few hundreds of nanometres thick, which reduces the potential problems of increase of resistance and reduction of the photovoltage. Depending on the spatial dimensions where the modulation of refractive index is found, we will refer these structures as one, two, or three dimensional photonic crystals (1DPC, 2DPC, or 3DPC, respectively) (Joannopoulos et al. 1995). The interference effects associated with these periodic dielectrics give rise to the opening of a photonic band gap whose effect is detected as a maximum in the specular reflectance spectrum of the structure. In the following section, the effect of integrating both 3DPC and 1DPC in DSSC is described.