Dye-sensitized solar cell

The Grätzel cell (including dye-sensitized solar cell, dye - sensitized solar cell english, short DSSC, or DSC DYSC ) is used to convert light energy into electrical energy. It is an application of bionics, which is called according to their function and electrochemical dye solar cell. This solar cell is named after Michael Grätzel (EPFL, Lausanne, Switzerland ), which they invented in the early 1990s and patented in 1992.

The electrochemical cell used in the dye-sensitized solar absorption of light is not a semiconductor material, but also organic dyes, for example the leaf chlorophyll.

Construction

The Graetzel cell is to each other of two planar (glass) electrode with a distance of typically 20 to 40 microns. The two electrodes are on the inside with a transparent, electrically conductive layer (e.g., FTO = English Fluorine doped tin oxide, fluorine -doped tin dioxide dt, F: SnO 2 ) coating, having a thickness of typically 0.5 microns. The two electrodes are named in accordance with their function, the working electrode (generation of electrons) and the counter electrode. On the working electrode, a about 10 microns thick, nanoporous layer of titanium dioxide ( TiO2) is applied. On its surface, in turn, a single layer of a photosensitive dye is adsorbed.

On the counter electrode is a few microns thick catalytic layer is (usually platinum). The area between the two electrodes is filled with a redox electrolyte, for example, a solution of iodine ( I2), and potassium iodide.

Function

This process is - simply put - a technical photosynthesis represents the functioning of the cell, however, is still not understood in detail.

The redox I-/I3- is in principle an electron " transport " or " conductive " fluid. The wetted with TiO2 dye is applied in a very thin layer on a TCO glass ( eg ITO glass). TCO glass is glass coated with an electrically conductive transparent oxide. The counter electrode is usually a surface coated with graphite or platinum plate is used.

In general, based on ruthenium dyes are used, but also blackberry and Hibiskusteeextrakte ( anthocyanins ) are suitable which adhere well in a monomolecular layer on the TiO2. Titanium dioxide is an n-type semiconductor films and nano a suitable material. But it is in the visible region is not sensitive to and absorbed only in the near UV range, since the energy band gap between the valence band and conduction band is 3.2 eV which corresponds to a wavelength smaller than 400 nm, an electron from the valence band into the conduction band to transport. Colorants such as anthocyanins are able to bind via hydroxyl groups on the TiO2 surface and to sensitize the semiconductor in the visible region of the spectrum by means of energy transfer.

Suggestion:

The excited dye molecule (Fs *) transfers electrons to the conduction band of TiO2.

The resulting atomic iodine at the anode unites the molecule ( I2), and this reacts with iodide ions I-to I3. From these molecular ions iodide 3, I- regenerated again at the cathode.

Some scientific questions that tie directly to the items highlighted in the graphics sub-processes (1 ) to (3 ), have been clarified in the last ten years. For example, the processes (1 ) and ( 3) were measured directly by time-resolved measurement techniques, with the result that the injection process ( 1) less than 25 fs takes, required the return of the electron from the TiO2 to the ionized dye milliseconds, with the addition of I3-/I--Redoxsystems but the dye is regenerated after about 100 ns.

Significant performance improvements were achieved by coating the cathode with a conductive polymer such as polypyrrole.

Animated presentation on the functioning

• Dielectric (glass)
• Coated with conductive material (eg SnO2 oxide)
• Semiconductor layer TiO2
• Dye molecules are chemically adsorbed on the large surface of the porous nanocrystalline TiO2
• Electrolyte with a redox -active ion pair typically iodide, the catalyst layer (for example, graphite, platinum, carbon black)

Importance

The advantages of the Graetzel cell basically can lie in the low production cost and low environmental load in production. The cell may use well diffused light compared to the conventional solar cell. Cells could be produced in the laboratory to 12.3 % conversion efficiency ( certified) in an area of ​​1 cm ². Commercially available modules have an efficiency in the range of 2 to 3%. One of the challenges for Grätzel cells is the stability over a long period of operation. This is especially true at high temperatures without light. In studies from the year 2003, the efficiency was after 1000 hours storage at 80 ° C in the dark by about 6 % (?) After. In a 2011 study published in the stability is considered sufficient for 40 years operating time in Central Europe and for 25 years in Southern Europe. According to its inventor increases in efficiency up to 31% for single cells are conceivable.

Scale-up

A major hurdle for the dye solar cell technology on their way from the laboratory scale to large-scale applications is the long-term stable sealing the electrolyte. When solutions exist, mainly hot-melt polymer glue, epoxy glue and glass solders. In particular glass solder have the potential to provide a chemically and thermally stable long-term sealing.