Efficient and Stable Solid-State Dye-Sensitized Solar Cells by the Combination of Phosphonium Organic Ionic Plastic Crystals with Silica

Remarkably efficient quasi-solid-state dye-sensitized solar cells (DSSCs) have been fabricated using organic ionic plastic crystal electrolytes based on a small triethyl(methyl)phosphonium [P1222] cation and two types of sulfonamide anions, bis(fluorosulfonyl)amide (FSA) and bis(trifluoromethanesulfonyl)amide (TFSA), in combination with varying amounts of silica (SiO2). Solar cell efficiencies of up to 7.4% were obtained, which is comparable to our benchmark efficiencies of liquid (acetonitrile) electrolyte-based devices. Such a high efficiency for DSSCs using quasi-solid-state electrolytes is attributed to improved ionic conductivity, enhanced redox couple transport, improved interfacial interaction between the electrolyte and the electrode as well as decreased resistance at both electrode interfaces. Notably, the devices with the silica-containing electrolytes displayed excellent stability after 5 months of storage, with the most stable devices, formed with either plastic crystal electrolyte containing 2% silica, showing no decrease in efficiency.