The effect of liquid crystal electrolyte modification on the efficiency of organic photovoltaic cells

In many modern devices used to convert or store electricity, such as dye-sensitized solar cells (DSSCs), fuel cells, lithium-ion batteries or supercapacitors, one of the critical elements is the organic electrolyte, the stability and physicochemical properties of which significantly affect the efficiency of the processes of converting or storing electrical energy. The essence of the concept of using liquid crystals in such devices is that properly ordered structures at the nanometer scale lead to an increase in ionic conductivity in a specific direction and fulfill the role of stabilizing the system mechanically and thermally. Moreover, temperature induction of phase transitions enables switching off functions in a given electrolytic structure.

DSSCs with porous semiconductor titanium dioxide (TiO₂) electrodes were sensitized using ruthenium-based dyes purchased from Solaronix. In this experiment, the following ruthenium dyes were used: cis-diisothiocyanato-bis (2.2'-bipyridil-4.4'-dicarboxylic acid) ruthenium (II), known as N3; cis-diisothiocyanato-bis (2.2'-bipyrida-4, 4'-dicarboxylato) ruthenium (II) bis(tetrabutylammonium), marked as N719; and the amphiphilic ruthenium dye cis-diisothiocyanato-(2.2'-bipyridil-4.4'-dicarboxylic acid)-(2.2'-bipyridil-bipipyridil-4.4'-dinonyl) ruthenium (II), known in the literature as Z907. The electrolyte (AN-50) with a low viscosity contained iodide/tri-iodide as a redox couple, and a redox concentration of 50 mM was used.

The current–voltage (I-U) characteristics were determined for the ruthenium-based dyes mentioned above in order to check the influence of their structure on the efficiency of the DSSC cells. Next, it was checked what effect the addition of a nematic liquid crystal of 4- cyano-4'-pentylbiphenyl (5CB) to the iodide electrolyte had on the I-U characteristics. Modification of the I-U characteristics was found, in particular a change in the values of I_SC current and U_OC voltage.