Multi-layers of TiO2 nanoparticles in the photoelectrode and binary iodides in the gel polymer electrolyte based on poly(ethylene oxide) to improve quasi solid-state dye-sensitized solar cells

Abstract

A gel electrolyte based on poly(ethylene oxide) is optimized in order to improve dye-sensitized solar cells (DSCs) by varying the contents of a binary mixture of salts, LiI, and Hex4NI (tetrahexylammonium iodide). Two series of electrolytes, one excluding and the other including 1-butyl-3-methylimidazolium iodide (BMII) and 4-tert-butylpyridine (4TBP), are investigated. The added BMII and 4TBP improve the conductivity in electrolytes. The highest conductivities at all the measured temperatures are shown by the electrolyte which includes BMII and 4TBP along with the Hex4NI:LiI molar ratio of 3:2. This composition in gel polymer electrolyte exhibits relatively high ionic conductivities, 4.44 × 10−3 and 6.93 × 10−3 S cm−1 at 25 and 50 °C, respectively. Quadruple-layered and highly porous nanocrystalline photoelectrodes that are prepared by spin coating TiO2 nanoparticles of the size 13 and 21 nm were used for the DSC preparation. DSCs that are assembled with BMII and 4TBP added electrolytes exhibit higher efficiencies. The DSC fabricated using the electrolyte having performance enhancers along with Hex4NI:LiI molar ratio of 2:3 and the photoelectrode having quadruple layers of TiO2 nanoparticles exhibit the highest short-circuit current density (11.1 mA cm−2), open-circuit voltage (770 mV), and efficiency (5.58%). The stability of the DSC performances is monitored by measuring current-voltage as a function of time. The cell optimized in this study exhibits a good short-term stability. The positive effects of TiO2 nanoparticle multilayers in the photoelectrodes, as well as of binary salt and performance enhancers in the electrolyte, are successfully utilized to enhance the performance of DSCs.