Recent research progress on polymer electrolytes for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have attracted large attention due to their easy fabrication, low cost and high conversion efficiency. Electrolytes play an important role in the photovoltaic performance of the DSSCs and many efforts have been contributed to study different kinds of electrolytes with various characteristics such as liquid electrolytes, polymer electrolytes and so on. Because the leakage and the volatilization of liquid electrolytes hinder their practical applications in the DSSCs, polymer electrolytes with high ionic conductivity, excellent thermal stability and long-term stability of the DSSCs based on them are alternatives to liquid electrolytes especially for the quasi-solid-state DSSCs. In this paper, research on solid polymer electrolytes is summarized and the influence of salt concentration on ionic conductivity of solid polymer electrolytes is described and thoroughly explained. On the other hand, the advantages of gel polymer electrolytes (GPEs) are introduced. The factors affecting the ionic conductivity of GPE and the performance of their DSSCs, consisting of the polymer concentration and type, the iodide salts, the solvents and the temperature are discussed. The tendency and the reasons of their influence are expounded in detail. To enhance the properties of GPE, many strategies are taken such as the fabrication of porous structure in the GPE membrane, the incorporation of proton donors, the introduction of inorganic nanoparticles and the addition of pyridine derivatives. Their improving effect and the causes for the enhancement are set forth.