Performance enhancers for gel polymer electrolytes based on LiI and RbI for quasi-solid-state dye sensitized solar cells

Abstract

In this study, the effect of additives (enhancers) on efficiency enhancement in dye sensitized solar cells (DSSCs) containing two series of gel polymer electrolytes, one based on LiI and the other based on RbI have been systematically studied. Polyacrylonitrile (PAN) was used as the host polymer while the performance enhancers used in each case were tetrapropylammoniumiodide (Pr₄NI), the ionic liquid 1-methyl-3-propyl imidazolium iodide (MPII) and 4-tert-butylpyridine (4TBP) respectively. Appropriate amounts of the selected enhancers were incorporated one by one, in LiI based and RbI based gel electrolytes. The incorporation of Pr₄NI and MPII led to an increase in conductivity of the electrolyte, while 4TBP showed a decrease in conductivity. The maximum conductivity of 3.85 mS cm⁻¹ at room temperature was shown by the RbI based-series while for the LiI based series the maximum conductivity was 2.95 mS cm⁻¹. Each of these electrolytes with respective additives was used to fabricate quasi-solid state DSSCs. For the DSSCs based on the LiI containing series, a significant short circuit current density (J_sc) enhancement (161%) from 3.65 to 9.54 mA cm⁻² was observed due to the addition of Pr₄NI. This J_sc value further increased to 9.7 mA cm⁻² due to the addition of MPII and 4TBP. For the DSSCs with corresponding Rb based electrolytes with all three additives, the highest J_sc value obtained was 11.5 mA cm⁻². The incorporation of the three additives Pr₄NI, MPII and 4TBP collectively enhanced the open circuit voltages and the efficiencies of both LiI and RbI containing quasi-solid state DSSCs. Another important finding from this work is that rarely used RbI containing electrolytes exhibit superior DSSC performance compared to more frequently used LiI based electrolytes. Hence, RbI appears to be a better candidate compared to LiI to fabricate gel polymer electrolytes for DSSCs in general. The three additives have contributed to a remarkable efficiency enchantment in DSSCs by 449.3% for the LiI based electrolyte and by 35.7% for the RbI based electrolyte.