Improvement in durability of dye-sensitized solar cell (DSC) is very important subject for the practical usage. We have developed plastic film type DSC based on flexible polyethylenenaphthalate (PEN) film for heading for practical applications such as ubiquitous power sources.
Usually, DSC has an organic liquid electrolyte containing iode/iodine redox couple. Volatile organic electrolytes often decrease the durability, and therefore, many researchers have tried to replace them with solvent having higher boiling point, and also with ionic liquid.
We have been investigating organic solvent-based electrolyte as well as ionic liquid based electrolyte from the view point of durability for plastic film type DSCs. As a result, a plastic film DSC consisting of propylenecarbonate-based electrolyte maintained its energy conversion efficiency of 2% over 220 hours under a condition of 55˚C and 95% relative humidity. One of key materials damaging plastic DSC under durability test is lithium iodide, which damages ITO layer on plastic substrate. And therefore, we have succeeded to improve durability a plastic film type DSC by using ionic liquid based electrolyte without containing lithium iodide.