Enhanced ionic mobility and increased efficiency of dye-sensitized solar cell by adding lithium chloride in poly(vinylidene fluoride) nanofiber as electrolyte medium

Abstract

Wearable energy-harvesting devices have gained far-reaching interest during the past 5 years. Therefore, flexible electrodes and polymer nanofiber-based bendable separators, used as gel-like electrolytes, including poly(vinylidene fluoride) (PVdF) nanofibers are focused. However, the commonly used PVdF nanofibers are hydrophobic in nature, and hence, the mobility and ionic conductivity of iodide/tri-iodide $$ \left( {{\text{I}}^{ - } / {\text{I}}_{3}^{ - } } \right) $$ ions, within the polymer nanofiber host, are low. Here, we report an electrospun PVdF nanofiber-electrolyte composite separator between photoanode and counter electrode in dye-sensitized solar cell (DSSC), having lithium chloride (LiCl) salt in it, with the aim of improving the ionic conductivity of $$ {\text{I}}^{ - } / {\text{I}}_{3}^{ - } $$ ions, due to a high ionization potential of LiCl. The results show that by adding 1.0% LiCl in PVdF, a higher ionic conductivity of $$ {\text{I}}^{ - } / {\text{I}}_{3}^{ - } $$ ions with a value of 4.29 × 10−4 S cm−1 is obtained, compared to 3.45 × 10−4 for no salt added. Further, a lower charge transfer resistance (R CT) value at the electrode–electrolyte interface is also observed by using 1.0% LiCl for both symmetrical and full-cell structures of DSSC with the values of 1.57 and 1.884 Ω compared to 3.775 and 2.954 Ω, respectively, of the cells with no salt. Consequently, a higher overall cell efficiency was also obtained as the cells having 1.0% in PVdF showed 8.73% power conversion efficiency compared to 7.87% of the cells without LiCl. Moreover, compared to the normal DSSC with liquid electrolyte, the proposed nanofiber separator-made DSSC only lost 1.9% efficiency, showing its promise to be used in the next generation of flexible solar cells and textile-structured solar cells in future.