Quasi-solid dye-sensitized solar cells containing nanoparticles modified with ionic liquid-type molecules

Gel electrolytes for quasi-solid dye-sensitized solar cells (QDSC) are reported. The gel electrolyte consists of ionic liquids and nanoparticles modified with imidazolium cations. Ionic liquid-type gel electrolytes containing nanoparticles are well-known. The difference between previous reports and this report is that imidazolium cations are bonded to nanoparticles through Ti-O-CO bonds and long alkyl chains. The role of the long alkyl chains turns out to be critical for high performances. When unmodified nanoparticles are added into ionic liquids until the gel becomes of clay-like hardness, the photovoltaic performances decrease with an increase in the bare nanoparticle content. However, the decreases in photovoltaic performances are retarded when surface-modified nanoparticles are added. Photovoltaic performances increase with an increase in the chain lengths connecting nanoparticles and imidazolium cations. When the chain length becomes 12 and counter anion is I-, solidification occurs without losing the performance of DSCs having the parent liquid electrolytes. The photocurrents of QDSCs do not decrease even when the ratio (nanoparticles/ionic liquids) increases to 0.9 and the feature looks like hard clay. Ionic paths between nanoparticles are discussed. (c) 2006 The Electrochemical Society.