Absorption Of Dye-sensitized Solar Cells Research Articles

Enhanced optical absorption of dye-sensitized solar cells with microcavity-embedded TiO_2 photoanodes

This paper reports the enhanced performance of dye-sensitized solar cells (DSSCs) with microcavity-embedded nanoporous TiO2 photoanodes. For DSSCs with photoanodes composed of a stack TiO2 sublayers with microcavity concentrations arranged from low to high on the light illumination path, the short-circuit current density and the conversion efficiency were improved. A pronounced increase in optical absorption and incident monochromatic photon-to-current conversion efficiency in the long-wavelength region indicated that the enhancement of cell performance was due to the multiple scattering of light by the microcavities and the light confinement by the stack of TiO2 sublayers with a high-to-low effective index of refraction.

On the use of metal nanoparticles for enhancement of light absorption in dye-sensitized solar cells

Metal nanoparticles can be used to enhance light absorption in photovoltaic nanocrystalline dye-sensitized solar cells. Our calculations scrutinizing this idea indicate, however, that the ratio of the rate of the induced power absorption by dyes, surrounding a nanoparticle, and the rate of the power dissipation by a nanoparticle is typically much lower than 0.5. Thus, this enhancement of light absorption seems to be practically inefficient.

The Influence of Local Electric Fields on Photoinduced Absorption in Dye-Sensitized Solar Cells

The dye-sensitized solar cell (DSC) challenges conventional photovoltaics with its potential for low-cost production and its flexibility in terms of color and design. Transient absorption spectroscopy is widely used to unravel the working mechanism of DSCs. A surprising, unexplained feature observed in these studies is an apparent bleach of the ground-state absorption of the dye, under conditions where the dye is in the ground state. Here, we demonstrate that this feature can be attributed to a change of the local electric field affecting the absorption spectrum of the dye, an effect related to the Stark effect first reported in 1913. We present a method for measuring the effect of an externally applied electric field on the absorption of dye monolayers adsorbed on flat TiO(2) substrates. The measured signal has the shape of the first derivative of the absorption spectra of the dyes and reverses sign along with the reversion of the direction of the change in dipole moment upon excitation relative to the TiO(2) surface. A very similar signal is observed in photoinduced absorption spectra of dye-sensitized TiO(2) electrodes under solar cell conditions, demonstrating that the electric field across the dye molecules changes upon illumination. This result has important implications for the analysis of transient absorption spectra of DSCs and other molecular optoelectronic devices and challenges the interpretation of many previously published results.

Selective positioning of organic dyes in a mesoporous inorganic oxide film

Although sequential adsorption of dyes in a single TiO(2) electrode is ideal to extend the range of light absorption in dye-sensitized solar cells, high-temperature processing has so far limited its application. We report a method for selective positioning of organic dye molecules with different absorption ranges in a mesoporous TiO(2) film by mimicking the concept of the stationary phase and the mobile phase in column chromatography, where polystyrene-filled mesoporous TiO(2) film is explored for use as a stationary phase and a Brønsted-base-containing polymer solution is developed for use as a mobile phase for selective desorption of the adsorbed dye. By controlling the desorption and adsorption depth, yellow, red and green dyes were vertically aligned within a TiO(2) film, which is confirmed by an electron probe micro-analyser. The external quantum efficiency (EQE) spectrum from a solar cell with three selectively positioned dyes reveals the EQE characteristics of each single-dye cell.

Synthesis of TiO2 nanotubes film and its light scattering property

TiO2 nanotubes with diameters of 10 nm and lengths up to 600 nm were fabricated by directly using commercial TiO2 powders P25 as the precursors via sonication-hydrothermal combination approach. TiO2 nanotubes were characterized by means of X-ray powder diffractometer (XRD), scanning electron microscope (SEM), selected area electron diffraction pattern (SAED) and transmission electron microscope (TEM). The light scattering property of film electrodes modified with TiO2 nanotubes was studied and revealed that TiO2 nanotubes can be used as the light scattering centers to increase the light absorption in dye-sensitized solar cells. The TiO2 nanotubes film electrodes mixed with 10% small nanoparticles TiO2 had both strong light scattering property and fine mechanical characteristics, and this kind of electrodes can be used as electrodes in improving the conversion efficiencies of dye-sensitized solar cells.

Synthesis of TiO2 nanotubes film and its light scattering property

TiO2 nanotubes with diameters of 10 nm and lengths up to 600 nm were fabricated by directly using commercial TiO2 powders P25 as the precursors via sonication-hydrothermal combination approach. TiO2 nanotubes were characterized by means of X-ray powder diffractometer (XRD), scanning electron microscope (SEM), selected area electron diffraction pattern (SAED) and transmission electron microscope (TEM). The light scattering property of film electrodes modified with TiO2 nanotubes was studied and revealed that TiO2 nanotubes can be used as the light scattering centers to increase the light absorption in dye-sensitized solar cells. The TiO2 nanotubes film electrodes mixed with 10% small nanoparticles TiO2 had both strong light scattering property and fine mechanical characteristics, and this kind of electrodes can be used as electrodes in improving the conversion efficiencies of dye-sensitized solar cells.

Molecular-based concepts in PV towards full spectrum utilization

Molecular-based concepts offer the potential of low materials and processing costs in photovoltaics (PV), which is especially interesting if high efficiencies can be obtained. To accomplish high efficiencies, a better utilization of the solar spectrum is of high importance. The concept of two-photon absorption in dye-sensitized solar cells and full spectrum aspects of luminescent flat plates concentrators are discussed in this paper. The two-photon dye cell can be compared to a tandem solar cell on the molecular level. The luminescent concentrator offers the potential to employ full spectrum utilization in combination with static concentration of both direct and diffuse light.

Computer simulations of light scattering and absorption in dye-sensitized solar cells

The TiO2 electrode of dye-sensitized solar cells (DSC) consists of 10–30nm sized particles which are sintered together. The effective surface of the TiO2 electrode is increased up to 1000 fold by the nanoporous structure. It is covered with a layer of dye, so an acceptable overall absorption can be achieved. The absorption in the cell, and therefore the current, can be further enhanced by light scattering in the electrode. However, as larger particles are needed for effective light scattering, there will be the simultaneous effect of a decreasing effective surface. Computer simulations will be presented which show how the absorption can be increased by optimizing the size of the TiO2 particles. Starting from Mie theory applied to coated spheres, multiple scattering is calculated using a numerical solution of the radiative transfer equation. Certainly, the particles are sintered together and the assumption of independent scattering is not valid, but the qualitative results should still remain valid. These calculations predict that a suitable mixture of small particles, which result in a large effective surface, and of larger particles, which are effective light scatterers, have the potential to enhance solar absorption significantly. Furthermore, electrodes made of multiple TiO2 layers are investigated, each layer consisting of particles of different sizes.