KCS

Dye-Sensitized nanocrystalline TiO2 solar cells (DSSCs) have attracted considerable interest because of their high conversion of sunlight to electricity and easy fabrication. To overcome the prohibitive cost of ruthenium metal complexes, several groups have developed metal free sensitizers and obtained efficiencies in the range of 6 ~ 9%. However, a major factor for the low photoconversion efficiency of many organic dyes in dye-sensitized solar cell is due to the formation of dye aggregates on the semiconductor surface. Therefore, for obtaining efficient photoconversion based on organic dyes, aggregation needs to be avoided through the structural modification of the dye. The sharp and narrow absorption of organic sensitizers seriously reduce their light harvesting capabilities. In order to solve such weakness, the simultaneous absorption on TiO2 electrodes of the plural dyes, which have different absorption wavelength, was utilized to cover the whole visible region. Another approach is that stepwise cosensitization of TiO2 films utilizing Al2O3 layers using two dyes can be able to utilize to broaden the absorption spectrum. The third approach is to use the tandem cell in order to maximize the power conversion efficiency. Another important issue for organic dyes is the stability, which are generally less stable than metal complexes for redox reactions due to formation of unstable radicals. In order to incorporate these required properties, we have designed and developed novel unsymmetrical organic sensitizers. Novel organic sensitizers composed of donor, electron-conducting, and anchoring groups were engineered at molecular level and synthesized. Here, we show synthesis, characterization and photovoltaic properties of the several sensitizers. One of them, upon anchoring onto TiO2 film exhibit incident photon to current conversion efficiency 91%. The photovoltaic data revealed a short circuit photocurrent density of 19.55 mA/cm2, an open circuit voltage of 718 mV and a fill factor of 0.72, corresponding to an overall conversion efficiency of 10.15% under standard AM 1.5 sunlight. In this seminar, we would like to introduce the synthesis of a variety of dyes and their photovoltaic properties.