Enhancing the performance of dye-sensitized solar cells by incorporating nanomica in gel electrolytes

Gel-type dye-sensitized solar cells (DSSCs) were fabricated with 5.0 wt% polyvinyidene fluoride-co-hexafluoro propylene (PVDF-HFP) in methoxy propionitrile (MPN) as gel polymer electrolyte (GPE), 1-butyl-3-methylimidazolium iodide (BMII)/iodine (I₂) as redox couple, 4-tertiary butyl pyridine (TBP) and guanidine thiocyanate as additives. The incorporation of alkyl-modified nanomica (AMNM) in the PVDF-HFP gel electrolytes caused the reduction of crystallization of PVDF-HFP, which was confirmed by X-ray diffraction (XRD) analysis. The short-circuit current density (J_SC) of the cell increased due to the decrease of diffusion resistance, as judged by the electrochemical impedance spectra (EIS) analysis, while the open-circuit voltage (V_OC) remained almost the same. As the loading of AMNM in the PVDF-HFP gel electrolyte was increased to 3.0 wt%, the J_SC and power conversion efficiency (η) of the cells increased from 8.3 to 13.6 mA/cm² and 3.5% to 5.7%, respectively. However, the J_SC decreased as the loading of AMNM exceeded 3.0 wt%. At higher AMNM loadings, nanomica acted as a barrier interface between the electrolyte and the dye molecules to hinder electron transfer, and thus reducing the cell's photocurrent density. Furthermore, the DSSCs fabricated by dispersing polymethyl methacrylate (PMMA) microspheres in the TiO₂ electrode with the GPE containing 3.0 wt% AMNM improved the η to 6.70%. The TiO₂ films would exhibit larger porosity by blending with PMMA, leading the penetration of GPEs into the porous TiO₂ easier, thus improving the contact between the dye-adsorbed TiO₂ surfaces and the GPEs, as characterized by EIS. Moreover, the η of gel-type DSSCs with a 25 μm thickness of surlyn reached 7.96% as compared with 6.70% for the DSSCs with a 60 μm surlyn.