High-performance gel-type dye-sensitized solar cells using poly (methyl methacrylate-co-ethylacrylate)-based polymer gel electrolyte with superior enduring stability

We fabricated high-performance gel-state dye-sensitized solar cells (DSSCs) using TiO₂ nanoparticles (NPs) and one-dimensional TiO₂ nanotube (NT) arrays as electrodes and a polymer gel electrolyte (PGE), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA), as a gelator in 3-methoxypropionitrile (MPN). MPN instead of acetonitrile (ACN) was used as a solvent to prepare PGE to overcome the drawback of high volatility of ACN so as to improve the long-term stability of the devices. The viscosities of the PGEs containing varied concentrations of PMMA-EA copolymer (4-13 wt%) were measured to obtain the gel to liquid phase transition temperature (T_p) of the PGEs. T_p systematically increased with increasing concentration of PMMA-EA. We found that the as prepared PGE showed the best electrical conductivity of 1.6 mS cm^-1 at 10 wt% of PMMA-EA, which is comparable with the value of the liquid electrolyte (1.7 mS cm^-1). By employing 10 wt% of PMMA-EA as PGE in MPN, the gel-type NT and NP-based devices exhibited power conversion efficiencies (PCE) 6.3 and 8.4%, respectively, which are comparable to those of the corresponding liquid-type counterparts, PCE = 6.4 and 9.1%, respectively. In addition, the enduring stability of MPN-based gel-state device was found to retain a high device efficiency for a long period under thermal and light-soaking dual stress.