Coupling of Titania Inverse Opals to Nanocrystalline Titania Layers in Dye-Sensitized Solar Cells

Abstract

We report a quantitative comparison of the photoaction spectra, short circuit current densities, and power conversion efficiencies of dye-sensitized solar cells (DSSCs) that contain bilayers of nanocrystalline TiO2 (nc-TiO2) and titania inverse opal photonic crystals (PCs). Cells were fabricated with PC/nc-TiO2 and nc-TiO2/PC bilayer films on glass/tin oxide anode of the cell, as well as in a split configuration in which the nc-TiO2 and PC layers were deposited on the anode and cathode sides of the cell, respectively. Incident photon current efficiencies at single wavelengths and current-voltage curves in white light were obtained with both cathode and anode side illumination. The results obtained support a model proposed by Miguez and co-workers, in which coupling of the low refractive index PC layer to the higher index nc-TiO2 layer creates a standing wave in the nc-TiO2 layer, enhancing the response of the DSSC in the red region of the spectrum. This enhancement is very sensitive to the degree of physical contact between the two layers. A gap on the order of 200 nm thick, created by a polymer templating technique, is sufficient to decouple the two layers optically. The coupling of the nc-TiO2 and PC layers across the gap could be improved slightly by treatment with TiCl4 vapor. In the bilayer configuration, there is an enhancement in the IPCE across the visible spectrum, which is primarily caused by defect scattering in the PC layer. There is also an increase of 20-50 mV in the open circuit photovoltage of the cell. With anode side illumination, the addition of a PC layer to the nc-TiO2 layer increased the efficiency of DSSCs from 6.5 to 8.3% at a constant N719 dye loading of 155-160 nmol/cm2.

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

“…11,19 Recently, Lee et al presented a new material route which enabled the beneficial layer sequence by infiltrating and thereby protecting the mesoporous underlayer with a block copolymer. 20 They subsequently characterized the effect of such a double layer structure in great detail. They found, however, that their material lacked the intimate physical contact between the nanoporous TiO 2 and TiO 2 inverse opal layers that is needed to achieve resonant modes.…”

“…10,20 However, the theoretical work by Usami shows that random scattering in DSCs should most efficiently occur at λ ≈ 1.33d, where d is the diameter of the scattering object. 40 For our feature sizes, random scattering would therefore occur in the deep blue of the spectrum.…”

“…16 Lee et al's approach of adding a photonic crystal top layer has resulted, however, only in a weak shift of the absorption properties due to the photonic structure which they assigned to a lack of physical contact between the layers and a rough interface. 20 In contrast, our straightforward fabrication method provides for close contact and a smooth interface between the mesoporous titania and the photonic crystal. This enables a significant enhancement in specific parts of the action spectrum as well as additional charge carrier generation arising from the photoactive material of the photonic crystal, which is now a functional part of the DSC.…”

Pore size dependence of self-assembled type photonic crystal on dye-sensitized solar cells efficiency utilising Chlorine e6

“…A previous study of DSSCs incorporating an inverse opal primarily considered the harvesting effect of the incident light [12]. Miguez et al [13] suggested that photoelectric conversion efficiency could be improved by utilising an inverse opal with a particle size of approximately 200 nm.…”

“…Mallouk et al reported a 26 % improvement of light harvesting efficiency at 400-750 nm by combining a selfassembled photonic crystal (TiO 2 inverse opal) with DSSCs [10]. They reported that an increase in incident light path length generated by Bragg diffraction and defect scattering in the inverse opal layer resulted in the enhancement of the visible wavelength [11,12].…”