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Modelling of dye solar cells with hole conducting polymer / Modellierung von Farbstoffsolarzellen mit polymerem Lochleiter

  • Wagner, J.
Publication Date
Jan 01, 2004
OpenGrey Repository


DSCs consist of dye molecules, that are chemically bonded to the surface of a porous titanium dioxide layer. This layer is deposited on a front electrode (usually a glass, covered a transparent conducting oxide). The pores are filled with a redox electrolyte that serves as media for charge carrier transport from the dye to the back electrode. Light is absorbed from the dye by exciting an electron from the highest unoccupied molecular orbital (HOMO) to the lowest occupied molecular orbital (LUMO). The electron is injected into the conduction band of the titanium dioxide and transported to the TCO-electrode. The ionized dye molecule is regenerated by the redox system. In this work the liquid electrolyte has been substituted by a hole conducting polymer, as the sealing of the cell is still an unsolved problem. As the efficiencies of these cells are far below of DSCs containing a liquid electrolyte, two different attempts have been undertaken to enhance the performance. With the Laser Induced Secondary Neutral Particles Mass Spectroscopy it has been determined that the pore filling with polymer is very poor in DSC that have been build by a conventional method. Consequently only a small part of the dye molecules are in contact with the hole conductor, a big amount of current is lost. Therefore a new cell concept has been developed. Instead of bringing up the different layers successively, a mixture of titanium dioxide, dye and polymer is brought up in one step and pressed with 300bar afterwards. With this method a good poor filling is achieved, but the efficiencies are still too low by using PEDOT as hole conducting polymer. Therefore a two dimensional model has been developed in order to determine the dominating mechanisms inside the cell. The model simplifies the porous titanium dioxide layer and calculates the distribution of the electrical potential and the charge carrier densities inside the cell. The Poisson and continuity equation are solved by iteration. I/V curves can be calculated with the model and the distribution of physical variables, such as electrical field, fermi level and current densities can be determined. Parameter variation can easily be carried out and the influence on the cell characteristics can be studied. For efficient solar cells it is important to prevent the recombination at the titanium dioxide/polymer interface. As further result it has become clear, that a good hole transport to the back electrode is essential for a high efficiency of the cell. But the good hole conductivity of the polymer should not be based on a high dark concentration of holes. In this case excess recombination will occur upon illumination at the titanium dioxide/polymer interface and decrease the photo current. The conductivity shall be based on a good hole mobility of the polymer. / Available from: <a href= target=NewWindow></a> / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / SIGLE / DE / Germany

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