Efficiency enhancement by mixed cation effect in polyethylene oxide (PEO)-based dye-sensitized solar cells

Abstract

The enhancement in efficiency of N719 dye-sensitized solar cells (DSSCs) by a mixed cation iodide salt mixture is investigated. The gel electrolyte used in the glass/FTO/nano-porous TiO2/gel electrolyte, I2/Pt/FTO/glass solar cell structure, consists of tetrapropylammonium iodide (Pr4NI) and potassium iodide (KI) in a plasticized polyethyleneoxide (PEO) host. The salt composition is varied to optimize the efficiency. With 100 wt% KI and 100 wt% Pr4NI efficiencies under AM 1.5 illumination are 3.75 and 3.13 %, while 66.7 w% KI composition shows the highest efficiency of 4.44 %. This is an efficiency enhancement of about 18 %. DC polarization measurements established the predominantly ionic behavior of the electrolytes. Results also show that the variation of efficiency with salt composition essentially followed the same trend as the variation of short circuit photocurrent density (JSC), which appears to be governed by the iodide ion conductivity. The above observations are further supported by photovoltage decay measurements where the electron recombination life time, τe, has the smallest value for the highest efficiency solar cell.