Amphiphilic Dye for Solid-State Dye-Sensitized Solar Cells
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Amphiphilic Dye for Solid-State Dye-Sensitized Solar Cells Lukas Schmidt-Mende, Shaik M. Zakeeruddin and Michael Grätzel Institut des Sciences et Ingénierie Chimiques (ISIC), Laboratoire de Photonique et Interfaces (LPI), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
ABSTRACT We report a solid-state dye-sensitized solar cell with a record efficiency of 4% under simulated sunlight (AM1.5global, 100mW/cm2). This was made possible by using a new amphiphilic dye with hydrophobic spacers in combination with spiro-OMeTAD. We attribute the significant improvement in the device performance to the self-assembly of the dye to form a compact layer on the TiO2 surface and to the hydrophobic chains working as blocking layer between spiro-OMeTAD and TiO2 to reduce the back electron transfer. In addition, we studied the influence of nanoporous TiO2 film thickness on the performance of the device. These results demonstrate the high potential for solid state dye sensitized solar cells to compete with amorphous silicon cells as low cost alternative.
INTRODUCTION The world energy consumption is raising, which makes the limitation of fossil fuels more and more apparent. Oil prizes are as high as never before. If it does not succeed to find cheap and easy accessible renewable energy sources the energy problem will further increase in the near future. This is certainly one reason, why the market of solar cells is one of the fastest growing markets, although the production of conventional solar cells is expensive and combined with a high energy consumption. Therefore the interests in and the perspectives of cheap alternative solar cells are very high. Dye-sensitized solar cells are a viable alternative for conventional solar cells. Since the first report of a highly efficient dye-sensitized solar cell in 1991[1] many groups are working on this type of cell and could improve the efficiency further[2-4]. Values exceeding 10% efficiency at one sun illumination have been reached[5]. It seems to be advantageous to replace the liquid electrolyte of these cells with a solid holeconductor to avoid any sealing and long-term stability problems. Not only the possibility of low cost production is an important advantage over conventional solar cells, also the versatile design possibilities, such as production of flexible cells and differently colored devices. We report here a solid-state dye-sensitized solar cell that has an efficiency of 4% under simulated sunlight (AM 1.5 global, 100mW/cm2)[6] with an amphiphilic ruthenium sensitizer. EXPERIMENT The structure of our cells is schematically shown in Figure 1. The cells consist of a F-doped SnO2 conducting glass substrates onto which a compact TiO2 layer was deposited by spray pyrolysis. This is necessary to avoid direct contact between the holeconductor and the SnO2, which would short circuit the cell. The holeconductor forms an ohmic contact to the SnO2 and charges would recombine at this interface. A dense TiO2 blocking layer impedes this current
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