The optimization of the conversion efficiency of dye sensitized solar cells (DSC) has become a key issue nowadays due
to the search for alternative energy resources. Different approaches based on the optical absorption enhancement can be
realized in this type of solar devices by modifying the optical design of the cell. In this respect, novel porous and highly
reflecting one-dimensional photonic crystals (1DPC) have been recently implemented in DSC due to their great potential
for the manipulation of light propagation. The periodic structure is built by alternating layers made of different types of
nanoparticles that allow us to obtain a wide and intense Bragg reflection peak. The photonic crystal, with a thickness of
just half-micron, is able to efficiently localize incident light within the nc-dyed TiO<sub>2</sub> electrode in a targeted wavelength
range. So, significant optical absorption amplification in a wide spectral range occurs in these structures that combine the
presence of a highly reflecting photonic crystal and a layer of absorbing material, being therefore enhanced the
photogenerated current. Average power conversion efficiencies are improved between 15% and 30% with respect to the
reference value attained for standard electrodes with no photonic crystal coupled.
The solar-to-electric power conversion efficiency of dye sensitized solar cells can be greatly enhanced by integrating a porous and highly reflecting photonic crystal in the device. The light harvesting enhancement is based on the enlargement of optical absorption caused by longer matter-radiation interaction time, which takes place at certain ranges of wavelengths. Photons are localized within the dye-sensitized electrode due to the effect of the photonic crystal, so the probability of optical absorption, and therefore the photogenerated current, is enhanced. The proposed photonic crystals are porous to allow a proper flow of the electrolyte through it and to prevent the introduction of internal resistance in the cell, which might alter the charge transport dynamics.
The light harvesting enhancement observed when photonic colloidal crystals are integrated in dye sensitized titanium
oxide solar cells is investigated herein. Such absorptance increment is explained in terms of slow photon propagation at
certain ranges of wavelengths lying within the photonic pseudogap and partial localization in an absorbing layer placed
onto the colloidal lattice. Based on those findings, not only recently reported experiments have been satisfactorily
explained, but also new optical designs for the dye-sensitized solar cells (DSSC) are proposed. The new arrangement
consists of piling up different lattice constant crystals leading to light harvesting enhancement in the whole dye
absorption range. We provide the optimum structural features of such photonic crystal multilayer needed to achieve a
photocurrent efficiency enhancement of around 60% with respect to standard dye-sensitized solar cells.