High efficiency dye-sensitized solar cell based on a novel gel polymer electrolyte containing RbI and tetrahexylammonium iodide (Hex4NI) salts and multi-layered photoelectrodes of TiO2 nanoparticles

Abstract

High efficiency dye sensitized solar cells (DSSCs) have been achieved using a novel polymer gel electrolyte containing RbI and tetrahexylammonium iodide (Hex4NI) binary salts in combination with multi-layered TiO2 photoelectrodes. Performance enhancers were incorporated to the electrolyte to improve the efficiency in the DSSCs. Varying the salt mass fraction, showed that the conductivity in the electrolyte increases with increasing amount of RbI. The highest ionic conductivity of 4.19 mS cm−1 is exhibited by the electrolyte sample with RbI:Hex4NI weight ratio of 3:1 at 25 °C. The temperature dependence of the electrolytes shows Arrhenius behavior. It is found that the electrolyte with RbI:Hex4NI weight ratio of 1.06:1 is more suitable for DSSC's applications and it has a conductivity of 3.77 mS cm−1. A colloidal suspension of P25 TiO2 nanoparticles was used to make the spin coated photo-anodes in the form of stacks of 1–6 layers. The formation of a highly uniform and porous structure is observed with increasing number of layers from scanning electron microscopy and X-ray diffraction studies revealed that the layers are predominantly anatase phase with crystallite size of 19–22 nm. The band gap was estimated to be around 3.22 eV based on UV–Visible spectroscopy and found to be decreasing slightly with increasing layer thickness. The maximum efficiency of 7.5% and an impressively high current density of 20 mA cm−2 were observed for the 4-layer device with the new gel electrolyte based on RbI and Hex4NI. This study not only brings reliability and consistency to the ways of preparing well-ordered TiO2 photo-anodes but also offers the possibility of low-cost practical and highly efficient quasi-solid state DSSCs.