Development of solid polymer electrolytes based on sodium-carboxymethylcellulose (NaCMC)-polysulphide for quantum dot-sensitized solar cells (QDSSCs)

Sodium-carboxymethylcellulose (NaCMC) films have been developed by solution casting technique. The films were soaked into an optimized aqueous polysulphide electrolyte containing 4 M sodium sulphide (Na2S) and 1 M sulphur (S). The optimized aqueous polysulphide electrolyte has the ambient conductivity of (1.46 +/- 0.02) x 10(-1) S cm(-1). The NaCMC films were soaked for different durations of 30, 60, 68 and 75 s. The highest room temperature ionic conductivity (RTIC) of (2.79 +/- 0.09) x 10(-5) S cm(-1) is exhibited by NaCMC film soaked in polysulphide electrolyte for 68 s. The conductivity-temperature relationship of NaCMC-based polysulphide solid polymer electrolytes (SPEs) follows the Arrhenius rule. The highest conducting SPE exhibits the lowest activation energy (E-A) value of 0.38 eV. Ionic coefficient of diffusion (D), ionic mobility (mu) and free ions concentration (n) of the SPEs were determined. The newly developed SPEs are used as electrolyte in quantum dot-sensitized solar cells (QDSSCs) application with the configuration FTO/TiO2/CdS/ZnS/SPE/Pt/FTO. Under 1000 W m(-2) illumination, QDSSC with CMC-68 SPE exhibits the highest power conversion efficiency (PCE) of 0.90%. The values of short circuit current (J(SC)) and PCE are closely related to electron lifetime and recombination rate.