Highly efficient gel electrolytes by end group modified PEG-based ABA triblock copolymers for quasi-solid-state dye-sensitized solar cells

To get highly efficient quasi-solid-state dye-sensitized solar cells (QSS-DSSCs) with long-term stability using polymer gel electrolytes (PGEs), well-defined ABA triblock copolymers ([Poly(methyl methacrylate)]₂-block-poly(ethylene glycol)) with different end functionality and components of I^-/I₃^- liquid electrolytes (LEs) are studied and optimized for the fabrication of PGE-based QSS-DSSCs. Triblock copolymers are synthesized in a one-step reaction using bifunctional PEG-macro chain transfer agent (MCTA) by reversible addition-fragmentation chain transfer (RAFT) polymerization. Due to the high reactivity and toxicity of sulfur-containing trithiocarbonate end groups, ABA triblock copolymers prepared from RAFT polymerization are further modified to sulfur-free 2-methylpropionitrile and 4-cyanopentanoic acid end functional triblock copolymers by radical-induced exchange reactions. Dodecyl trithiocarbonate end functional PEG-MCTA and triblock copolymers absorb UV-light in the region of 260–380 nm, whereas sulfur-free carboxylic acid and 2-methylpropionitrile end functional polymers do not absorb in that UV-light region. Among three different end functional polymers, the carboxylic acid end functional triblock copolymer has the highest thermal stability. Based on electrochemical parameters, photovoltaic performance, and long-term stability, 1,2-dimethyl-3-propylimidazolium iodide (DMPII) ionic liquid and 4-tert-butylpyridine (TBP) additive containing acetonitrile-based I^-/I₃^- LEs are effective for PGEs. The highest power conversion efficiency (PCE) for QSS-DSSCs achieved under simulated 1-sun illumination is up to 10.34%, which is comparable with the highest PCE of 10.39% for LE-DSSCs. Considering the high reactivity, thermal stability, UV-absorption, and the toxicity of the trithiocarbonate end group, the SGT-643-C triblock copolymer with carboxylic acid end group can be a promising candidate as a sulfur-free polymeric matrix for gel electrolytes of QSS-DSSCs.