Origin of enhanced light-harvesting in colloidal-crystal-based dye-sensitized solar cells.

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.