Polymer-dispersed MWCNT gel electrolytes for high performance of dye-sensitized solar cells

Abstract

A hybrid of polymer-dispersed multi-walled carbon nanotubes (MWCNT) was utilized in networking with the conventional composition of gel electrolyte in dye-sensitized solar cells (DSSCs) to purposely enhance the cell efficiency. The requisite polymer as the dispersant is structurally tailored for its functionalities consisting of poly(oxyethylene)-segmented amides and imides. The existence of the dispersant is multi-functional for first de-bundling the originally aggregated MWCNT and subsequently networking with the conventional gel electrolyte, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP)/LiI system. The gel electrolyte comprised of only 0.25 wt% MWCNT/POEM in the finely dispersed state was fabricated into a quasi-solid-state DSSC which showed high power-conversion efficiency (η) of 6.86% and short-circuit current density (JSC) of 15.3 mA cm−2 at the test of 100 mW cm−2 irradiation. The DSSC efficiency was significantly improved from the use of the unmodified gel electrolyte having the values of JSC = 9.6 mA cm−2 and η = 4.63%. The enhancement was further confirmed by the electrochemical impedance spectra analyses for the lowest Warburg resistance (Rw). The fine dispersion of MWCNT in the polymeric dispersant was characterized by UV-Vis, TEM, FT-IR and DSC. The finding indicates the role of MWCNT for homogenizing the amorphous PVDF–HFP and facilitating the diffusion state of I−/I3− ion pairs in this electrolyte system.