Light-trapping in dye-sensitized solar cells

We demonstrate numerically that photonic crystal dye-sensitized solar cells (DSSCs) can provide at least a factor of one-third enhancement in solar light absorption and power conversion efficiency relative to their conventional counterparts. Our design consists of a lattice of modulated-diameter TiO2 nanotubes filled with TiO2 nanoparticles and interstitial regions filled with electrolyte. This provides not only light trapping and absorption enhancement, but offers improved electrical transport through the nanotube walls. The nanotube array itself forms an extended 2D photonic crystal, and the spacing and diameter of tubes in the array are chosen to promote dielectric modes that concentrate light in the interior of the tubes. Linear and sinusoidal modulation over select regions of the nanotube diameter create a 3D photonic crystal and allow for enhanced anti-reflection and back-reflection, respectively. Further reduction of reflection losses is accomplished through the addition of triangular corrugation to the glass-air interface of the cell. Using a constant volume of dye-coated TiO2 nanoparticles our design gives a maximum achievable photocurrent density (MAPD) of 20.8 mA cm(-2) in 2D simulations. This is a 33% improvement over the MAPD for a simple planar cell geometry, and well above the record shortcircuit current density for C101-based cells. We also demonstrate that choosing a dye with a broader but weaker absorption profile compared to commonly used dyes would lead to even larger absorption enhancements.