Effect of D-limonene additive in copper redox-based quasi-solid-state electrolytes on the performance of dye-sensitized solar cells

In dye-sensitized solar cells (DSSCs), the copper redox mediator has been proven to enhance power conversion efficiency (PCE) due to the fairly low driving force for dye regeneration. In this work, we prepared six blended biopolymer-based electrolytes (E1 to E6) to regenerate N3 Dye absorbed in TiO2 for dye-sensitized solar cell application. The regeneration behavior of three different electron-withdrawing substituents on 2-(pyridin-2-yl) 1 H-benzo[d]imidazole ligands coordinated with copper metal, its forms [Cu(mpimb)(2)](1+/2+) (methyl 4-((2-(pyridin-2-yl) 1 H-benzo[d]imidazol-1-yl)methyl) benzoate), [Cu(pbimb)(2)](1+/2+) (4-((2-(pyridin-2-yl)-1 H-benzo[d]imidazol-1-yl)methyl) benzonitrile) and [Cu(ptpbi)2](1+/2+) (2-(pyridin-2-yl)-1(4-(trifluoromethyl) benzyl) 1 H-benzo[d]imidazole). Commencing their electrochemical and photophysical properties determines the molecular orbital energy level of the complex. A quasi-solid-state electrolyte (QSSE) medium is blended in a biopolymer host (pectin and 2-hydroxyethylcellulose). Additionally, a comparison study has been performed between commercially available pyridine-based-additive [tert-butyl pyridine (TBP)], and a bio-organic compound extracted from orange peel waste (1-methyl-4-(prop-1-en-2-yl) cyclohex-1-ene (limonene)) used as an additive material. Using these newly designed copper redox mediators and additives, the six sets of DSSCs devices has constructed. The cell structure is assembled as TiO2/N3 dye/electrolyte (E1 to E6)/Pt. Among the fabricated devices, C1 and C2 redox couples [Cu(ptpbi)(2)](1+/2+) having CF3 substituent exhibit maximum Voc and J(sc). Interestingly, the device with limonene additive exhibited PCE up to 4.4 %, whereas with TBP, it showed 4.0 % efficiency. The PCE results of the C2 device sustained some electrochemical factors such as Bulk Resistance (R-b = 142.0 Omega), Recombination Resistance (R-rec = 191.4 Omega), Charge Transfer Resistance (R-ct = 98.84 Omega), Chemical capacitance (C mu = 7.882 mu F), Ionic Conductivity (sigma = 2.816 x10(-04) S cm(-1)), electron lifetime (tau(n) = 16.24 mu s), Diffusion length (L-n =1.39 x 10(-01) mm).