Efficient quasi-solid state dye sensitized solar cell using succinonitrile : thiourea based electrolyte composition

Abstract

The present work demonstrates the application of a composite gel based electrolyte for the fabrication of quasi solid state dye sensitized solar cells (DSSCs). Two gel electrolyte compositions were prepared using poly-ethylene glycol (PEG), titanium di-oxide (TiO₂) and ionic liquids with only succinonitrile (SCN) and succinonitrile : thiourea (SCN : TU). Fabrication of DSSCs was carried out by sandwiching two gel electrolyte compositions between a dye sensitized photo anode and a platinum counter electrode. The electrolyte compositions were characterised using scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) studies. The presence of SCN : TU in the electrolyte introduced an interconnected network with titania-nano clusters embedded uniformly inside the host matrix. EIS and CV analysis demonstrated reduced charge transfer resistance and increased current density values. These results were found to be in accordance with current density–voltage measurements of DSSCs which revealed 5 times enhancement in short circuit current density and approximately 3 times enhanced efficiency of 2.38% with the addition of SCN : TU inside the electrolyte matrix. However, slight reduction in open circuit voltage (from 0.68 V to 0.53 V) on addition of SCN : TU was observed. This may be attributed to downward movement of the quasi Fermi level of titania relative to the redox potential of the electrolyte. These results were also confirmed by absorption spectroscopy analysis. The combination SCN : TU was found to be an efficient additive for quasi solid state electrolyte based DSSC applications.