PAN-Based Triblock Copolymers Tailor-Made by Reversible Addition-Fragmentation Chain Transfer Polymerization for High-Performance Quasi-Solid State Dye-Sensitized Solar Cells

Abstract

For efficient polymer gel electrolytes (PGEs) in quasi-solid-state dye-sensitized solar cells (QSS-DSSCs), six ABA triblock copolymers based on (poly(acrylonitrile-co-N-(isobutoxymethyl)acrylamide)- block-poly(ethylene glycol)-poly(acrylonitrile-co-N-( isobuto-xymethyl)acrylamide)) (P(AN-co-BMAAm)-b-PEG-b-P(AN-co-BMAAm)) with various copolymer compositions and molecular weights, coded as SGT-605, SGT-606, SGT-608, SGT-609, SGT-611, and SGT-612, have been synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using PEG-functionalized macro-RAFT agents. The effects of copolymer compositions and molecular weights in P(AN-co-BMAAm)-b-PEG-b-P(AN-co-BMAAm) triblock copolymers were investigated in terms of electrochemical properties and photovoltaic performance as PGEs. The ionic conductivity was increased with N-(isobutoxymethyl)acrylamide (BMAAm) composition of these triblock copolymers, which is attributed to the availability of free iodide ions by complex formation among acrylamide groups with Li+ ions. However, polymer gel electrolytes with high molecular weights enhance ionic conductivity due to the lower amount of polymers required for the gel formation. Thus, the photovoltaic performances of PGE-based QSS-DSSCs improved along with the increase in the molecular weight of the triblock copolymer. The addition of 7 wt % TiO2 nanofiller into PGEs produced a higher ionic conductivity and diffusion of I-3(-) than the corresponding PGEs. The resulting power conversion efficiency (PCE) of QSS-DSSCs using SGT-612/TiO2 composite PGEs under simulated 1-sun condition was 9.83% (V-oc, 792.8 mV; J(sc), 16.65 mA/cm(2); FF, 74.52%), which was higher than that of liquid electrolyte DSSCs (PCE 9.53%; V-oc, 743.8 mV; J(sc), 17.16 mA/cm(2); FF, 74.64%). The long-term device stability of PGE-based QSS-DSSCs was better than the liquid-state DSSCs.