Efficiency enhancement in dye-sensitized solar cells with a novel PAN-based gel polymer electrolyte with ternary iodides

Artikel i vetenskaplig tidskrift, 2015

The dye-sensitized solar cells (DSSCs) are promising, but their efficiency and stability require improvements. Quasi-solid-state DSSCs, based on gel polymer electrolytes, have exhibited reasonable performance with binary iodides. In this work, polyacrylonitrile-based gel polymer electrolytes were prepared using three iodide salts namely lithium iodide (LiI), 1-butyl-3-methylimidazolium iodide (BMII), and tetrapropyl ammonium iodide (Pr4NI) and investigated for their suitability for improving the performance of DSSCs. Hence, the LiI content was optimized for enhancement of both conductivity and DSSC performance employing fixed amounts of Pr4NI and BMII, and the compositions investigated had the chemical formula (PAN)(10)(EC)(25)(PC)(20)(BMII) (Pr4NI)(0.75)(LiI)(n)(I-2)(n/10). The highest room temperature ionic conductivity, 3.93 mS cm(-1), was obtained for the electrolyte sample with LiI molar fraction n = 1.75, out of the prepared set of electrolytes. This electrolyte in a DSSC with a single mesoporous layer of TiO2 produced the best efficiency of 5.41 % with J (sc) of 20.6 mA cm(-2). The changes in short circuit current density, open circuit voltage, and cell efficiency with the composition of the electrolyte are explained considering possible influences of cations in the electrolytes toward the electron injection from dye to TiO2, the electron diffusion through TiO2, shift of flat band potentials, and conductivity in the electrolyte. The incorporation of LiI into the electrolyte with the binary iodide system enhanced the efficiency by 30 % and the J (sc) by 62 % in the DSSCs fabricated with such electrolytes. This work uncovers the advantage of using ternary iodides in quasi-solid-state DSSCs rather than single or binary iodides.