Dye-Sensitized Solar Cell Based on a Three-Dimensional Photonic Crystal

Abstract

We present a material assembly route for the manufacture of dye-sensitized solar cells, coupling a high-surface mesoporous layer to a three-dimensional photonic crystal (PC). Material synthesis aided by self-assembly on two length scales provided electrical and pore connectivity at the mesoporous and the microporous level. This construct allows effective dye sensitization, electrolyte infiltration, and charge collection from both the mesoporous and the PC layers, opening up additional parameter space for effective light management by harvesting PC-induced resonances.KEYWORDS Photonic crystal, self-assembly, photovoltaics, dye-sensitized solar cell E ver since the pioneering work of O'Regan and Grät-zel, dye-sensitized solar cells (DSCs) have attracted great interest as a promising technology for future sustainable energy generation. 1 In DSCs, charge carrier generation takes place in a chemisorbed monolayer of photoactive dye which is sandwiched between a semiconductor oxide, usually mesoscopic anatase, and an electrolyte acting as electron and hole conducting materials, respectively. Using state-of-the-art ruthenium-based inorganic dyes, efficiencies higher than 11% have been reported. [2][3][4] DSCs are generally made from cheap and nontoxic components and can be designed in a variety of different colors and transparencies, which distinguishes them as an ideal photovoltaic concept for integrated architecture. It therefore seems only a matter of time before large scale production will follow. 5 In general, improvements in the overall power conversion efficiency have been centered on increasing the photovoltage through manipulation of the oxide, improving the photocurrent with new dyes, and increasing stability by better encapsulation. 5 While record-holding liquid electrolyte DSCs already achieve maximum quantum efficiency (photon-toelectron conversion) in the spectral range around 520 nm, light harvesting in the red and near-infrared (at the tail of the absorption spectra) is still relatively low. In solid-state devices, light absorption is generally limited by the film thickness, as thick mesoporous films prove difficult to infiltrate. 6 One way to successfully enhance light harvesting is the introduction of optical elements, such as highly scattering layers. These consist of large particles, that increase the photon path length in the cell. 7,8 This ubiquitous approach has the unfortunate effect of rendering the DSC opaque thus depriving it of one of its main advantages over competing technologies. As a result, photonic band gap materials in the form of 3D inverted TiO 2 opal or porous bragg stacks have been applied to DSCs to enhance light harvesting in specific partsofthespectrumwhileretainingthecelltransparency. 9-12 Several theoretical approaches report a variety of possible effects, including the localization of heavy photons near the edges of a photonic bandgap, 13 Bragg diffraction in a periodic lattice, 14 multiple scattering at disordered regions in the photonic crystal (PC), 15 and the for...

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