When it is referred the use of solid electrolytes it is generally accepted that people mean the use of p-type semiconducting materials either organic or inorganic. In the case of organic materials the most popular is spiro-MeOTAD which initially proposed by Gratzel and coworkers (Kruger et al., 2002). The recorded efficiency was about 4% while new organic semiconductors were appeared in the meanwhile. Polymer based solid electrolytes are usually referred as efficient alternatives to liquid based electrolytes but the efficiency is still poor. Polymer usually containing polyether units can be used as solid electrolytes in DSSCs. These types of electrolytes are solid ionic conductors prepared by the dissolution of salts in a suitable high molar mass polymer containing polyether units (de Freitas et al., 2009).
In the case of inorganic materials, CuSCN (O’Regan & Schwartz, 1998) and Cul (Tennakone et al. 1995) are the most popular, but the efficiency of the solar cells is lower than 2% because of the poor contact between TiO2 and p-type inorganic semiconductor. Optimized interface between the two different types of semiconductors and instability problems of copper based p-type semiconductors have to be improved before the p-n junction between them to be more efficient.