The structure of a dye-sensitized solar cell is shown in Figure (a), where the dye-sensitized solar cell is composed of a dye adsorbed nanocrystalline TiO2 film on a transparent conducting substrate, usually fluorine-doped tin oxide (FTO), a redox electrolyte and a nanoparticle platinum counter electrode. Iodide and triiodide are usually used as redox electrolyte. When dye absorbs incoming visible light, electrons in the ground state of dye are excited and photo-excited electrons are injected into the conduction band of TiO2 as can be seen in Figure (b). The photoinjected electrons are transported through the interconnected particle network and collected on the FTO substrate. The oxidized dyes are regenerated by reduction of iodide. Therefore, dye molecule plays an important role in generating photoexcited electrons. TiO2 nanocrystalline film provides a pathway for photo-injected electrons to move from dye to transparent conducting substrate. Redox electrolyte delivers electrons from counter electrode to oxidized dye to regenerate dye.

 

Advantages and Major Applications of Dye-Sensitized Solar Cell

Since mesoporous TiO2 films are constructed with nano-sized (~ 20 nm in diameter) particles, the film is semi-transparent. Moreover, various colors are possible by tuning the HOMO-LUMO gap energies of dye molecules. These colorful and transparent characteristics are unique property of a dye-sensitized solar cell. Dye-sensitized solar cells cost only about 20% of a wafer-type Si solar cell price. Energy payback time (EPT), which is a kind of indicator to estimate cost of solar cells, for dye-sensitized solar cells is about 0.5 year under the condition of 1,700 kWh/m2 sun light, which is much shorter than the bulk Si solar cell (~4 year) and amorphous Si solar cell (~3 year). The shorter EPT is cheaper to manufacture as expected. It has been confirmed that the dye-sensitized solar cell shows relatively better performance under low light intensive conditions, such as cloudy days or facing north, when compared with crystalline silicon solar cells.

Therefore, dye-sensitized solar cell will be good for building window and car sun roof applications. See the colorful and transparent dye-sensitized solar cell window prototype manufactured using screen printing technique by KIST above.

Technology Transfer to Dongjin SEMICHEM CO. Ltd.

KIST technology covers the synthesis of all the materials to fabrication of high efficiency dye-sensitized solar cells and modules. KIST has technology for the preparation of a high quality nanocrystalline TiO2 colloid by using sol-gel and a high pressure hydrothermal process, screen printable TiO2 paste, N719 (ruthenium based red dye), N749 (ruthenium based green dye) and their purification using a column chromatographic method, and TiO2 film using a screen printer and a well-defined thermal sintering process. KIST is able to prepare a Pt film on FTO glass by chemical coating and the thermal reduction process, immidazolium iodides having different alkyl chain length and the formulation of high performance redox electrolytes. KIST holds high technology for the manufacturing process of dye-sensitized solar cells with a conversion efficiency of 11% which is comparable to the world's best efficiency (see the photocurrent- voltage curve, published in Phys. Stat. Sol. (a) in 2008). In addition, we can manufacture Z-series, W-series and monolithic type modules. Technology was transferred to Dongjin SEMICHEM company in 2008. Transferred technologies include dye purification and dye adsorption on metal oxide films, synthesis of TiO2 by hydrothermal method and formulation of TiO2 paste, coating, structure control and thermal treatment of TiO2 electrode on TCO substrate, a method for blocking layer formation, synthesis and formulation of liquid electrolyte systems and fabrication of high efficiency dyesensitized solar cells. Commercialization based on transferred technology from KIST is expected around 2012 by Dongjin SEMICHEM.