Well-defined triblock copolymer/TiO2 composite gel electrolytes for high-performance dye-sensitized solar cells

Abstract

A PEG-functionalized macro-RAFT agent was prepared by reacting a DCMBAT (S-dodecyl-S′-(α-cyano-α′-methyl-α′′-butanoic acid)trithiocarbonate) RAFT agent with poly(ethylene glycol) (PEG) in a Steglich esterification reaction. Subsequently, two types of triblock copolymers were prepared by utilizing the PEG-functionalized macro-RAFT agent, and they have structures of PEG-b-(P(AN-co-BMAAm))₂ (SGT-602) and PEG-b-(P(AN-co-DMAAm))₂ (SGT-604). SGT-602 and SGT-604 were successfully dissolved in a liquid electrolyte with acetonitrile (ACN) solvent. The gel electrolyte, SGT-604 or SGT-602, was electrochemically investigated by using a symmetrical dummy cell, in which a thin layer of the gel electrolyte solution is sandwiched between two identical electrodes, and introduced to dye-sensitized solar cells (DSSCs). A TiO₂ nanofiller was introduced into the gel electrolytes in order to improve cell performance with a fixed polymer content of 13 wt% and 15 wt% for SGT-602 and SGT-604, respectively. The optimized composition of the TiO₂ nanofiller was found to be 10 wt% of the total weight of the polymer gel electrolyte. The resulting TiO₂ composite gel electrolytes showed efficiencies of 9.30% and 9.39% for the TiO₂ composite gel with SGT-602 (J_sc: 17.98 mA cm⁻², V_oc: 733 mV and FF: 70.59%) and SGT-604 (J_sc: 17.90 mA cm⁻², V_oc: 746 mV and FF: 70.35%), which are comparable to those of liquid-state DSSCs (η: 9.86%, J_sc: 18.23 mA cm⁻², V_oc: 730 mV and FF: 74.05%). Electrochemical impedance spectra (EIS) and Tafel polarization curves were analyzed to explain the photovoltaic parameters. Finally, the efficiencies were traced under 1 sun illumination at 50 °C.