Photon Management in Dye Sensitized Solar Cells

Silvia Colodrero, Mauricio E. Calvo and Hernan Miguez

Instituto de Ciencia de Materiales de Sevilla Consejo Superior de Investigaciones Cientificas-Universidad de Sevilla

Spain

1. Introduction

Solar energy is nowadays one of the most promising future energy resources due to the depletion of fossil fuels, which supply the major part of all energy consumed worldwide. Among the different types of solar cell technologies, dye sensitization of mesoporous oxide based films has attracted a great deal of interest in the last few years because of the possibility it offers to achieve moderate efficiency devices at very low cost, being therefore an interesting alternative to conventional p-n junction solar cells. Dye sensitized solar cells (DSSC) consist of a nanocrystalline wide band gap semiconductor (usually TiO2), which is deposited onto a transparent conductive substrate, and on whose surface a dye is adsorbed. The cell is completed with a counterelectrode, and both electrodes are put into electrical contact by infiltrating a liquid electrolyte in between them. Light is absorbed by the dye and charges are separated at the interface between the dye and the metal oxide it is anchored to. The optimization of the conversion efficiency, that is the fraction of light intensity that is converted into electrical power, is a key issue for this type of solar systems. In this way, different modifications of the originally proposed cell have been made in order to improve its performance, most of them based on the use of different semiconductors, dyes or ionic conductor. There is also an increasing interest in employing nanostructures to improve solar energy conversion devices (Kamat, 2007).

Another interesting route to enhance the cell efficiency is to modify its optical design in order to improve the light harvesting efficiency (LHE) or absorptance within the cell. The approach that has been explored the most has been the use of a diffuse scattering layer made of large TiO2 colloids that are either deposited onto the nanocrystalline electrode or mixed with the nanocrystalline titania (nc-TiO2) slurry. In both cases, increase of the optical light path within the absorbing layer rises the matter-radiation interaction time thus enhancing the probability of photon absorption. It has to be bear in mind that any structure introduced in the cell must permit the electrical contact between the electrolyte and the sensitized semiconductor slab, which forces it to have a porosity capable of sustaining the flow of charges. In recent times, different alternatives to light management in DSSC are being proposed and realized due to the development of novel porous periodic photonic nanostructures that can be easily integrated in these devices. The aim of this chapter is to give a brief review of the efforts performed to improve the light harvesting in DSSCs

through the optimization of their optical design and provide a detailed description of the new emerging possibilities based on coupling dye-sensitized electrodes to different periodic photonic nanostructures. It will be shown that they have a great potential for the manipulation of light propagation. A detailed description of the integration processes used, of the different mechanisms of light harvesting enhancement that take place, and of actual examples showing the improvement of performance achieved will be presented in this chapter.

Updated: August 23, 2015 — 2:51 am