Nanoclay minerals play a promising role as additives in the liquid electrolyte to form a gel electrolyte for quasi-solid-state dye-sensitized solar cells, because of the high chemical stability, unique swelling capability, ion exchange capacity, and rheological properties of nanoclays. Here, we report the improved performance of a quasi-solid-state gel electrolyte that is made from a liquid electrolyte and synthetic nitrate-hydrotalcite nanoclay. Charge transport mechanisms in the gel electrolyte and nanoclay interactions with TiO2/electrolyte interface are discussed in detail. The electrochemical analysis reveals that the charge transport is solely based on physical diffusion at the ratio of [PMII]:[I2] = 10:1 (where PMII is 1-propyl-3-methylimidazolium iodide). The calculated physical diffusion coefficient shows that the diffusion of redox ions is not affected much by the viscosity of nanoclay gel. The addition of nitrate-hydrotalcite clay in the electrolyte has the effect of buffering the protonation process at the TiO2/electrolyte interface, resulting in an upward shift in the conduction band and a boost in open-circuit voltage (VOC). Higher VOC values with undiminished photocurrent is achieved with nitrate-hydrotalcite nanoclay gel electrolyte for organic as well as for inorganic dye (D35 and N719) systems. The efficiency for hydrotalcite clay gel electrolyte solar cells is increased by 10%, compared to that of the liquid electrolyte. The power conversion efficiency can reach 10.1% under 0.25 sun and 9.6% under full sun. This study demonstrates that nitrate-hydrotalcite nanoclay in the electrolyte not only solidifies the liquid electrolyte to prevent solvent leakage, but also facilitates the improvement in cell efficiency.
X. Wang, Kulkarni, S. A., Ito, B. Ieiri, Batabyal Sudip Kumar, Nonomura, K., Wong, C. Cheong, Grätzel, M., Mhaisalkar, S. G., and Uchida, S., “Nanoclay gelation approach towards improved dye-sensitized solar cell efficiencies: an investigation of charge transport and shift in TiO2 conduction band”, ACS Applied Materials & Interfaces, vol. 5, pp. 444-450, 2013.