Theoretical simulations of optical confinement in dye-sensitized nanocrystalline solar cells

The application of light scattering of submicron TiO2 particles to dye-sensitized nanocrystalline photoelectrochemical cells is examined theoretically. Monte Carlo simulations reveal that the increase of absorption path length of photons in nanocrystalline films and optical confinement due to total reflections at solar cell surfaces improve light absorption in the sensitized films remarkably. Contribution of optical confinement to the improvement is much greater than that of the increase of absorption path length. Quantum efficiencies are calculated, considering the recombination of electrons in the nanocrystalline films. The application of light scattering improves the quantum efficiencies remarkably, especially in long wavelength lights. Optical confinement permits utilization of thinner sensitized films. Distributions of light absorption in the scattering films are also discussed. The distributions are not represented as exponential expressions due to light reflections in the vicinities of transparent conductive oxide (TCO) electrodes. Optical confinement decreases the light reflections and improves light absorption next to the TCO electrodes where generated electrons can diffuse without recombinations.