Sodium carboxymethyl starch-based highly conductive gel electrolyte for quasi-solid-state quantum dot-sensitized solar cells

Liquid-junction quantum dot sensitized solar cells (QDSCs) have been facing a long stability issue due to the volatilization and leakage of liquid electrolytes. Solidification of liquid electrolytes was expected to solve the main challenge for the application of QDSCs. Herein, a novel gel electrolyte was developed by solidifying conventional polysulfide aqueous solution with CMS-Na (Sodium Carboxymethyl Starch) as gelator. Due to its superior water absorbing and holding capacity as well as dimensional porous networks, the obtained CMS-Na gel electrolyte exhibits high conductivity and beneficial ion transport. Meanwhile, CMS-Na gel electrolyte could form a passivation layer coated on the surface of QDs/TiO2 via its strong coordination of carboxylate groups on CMS-Na polymer chains with metal ions, sequentially suppressing the charge recombination between photoanode and electrolyte. As expected, the constructed quasi-solid-state QDSCs exhibited a photoelectric conversion efficiency of 6.32%, which is comparable to that of liquid-junction QDSCs. Notably, light-soaking stability of the resultant QDSCs is significantly improved.