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 | 21 Dec 2012
X Wang, SA Kulkarni, BI Ito, SK Batabyal, K Nonomura, CC Wong, M Grätzel, SG Mhaisalkar and S Uchida
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 their high chemical stability, unique swelling ability, ion exchange capacity and rheological properties. Here we report the improved performance of a quasi-solid-state gel electrolyte comprising a liquid electrolyte and synthetic nitrate-hydrotalcite nanoclay. Charge transport mechanism 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. The calculated physical diffusion coefficient shows that the diffusion of redox ions is not much affected by the viscosity of nanoclay gel. The addition of nitrate-hydrotalcite clay in electrolyte has the effect of buffering the protonation process at TiO2/electrolyte interface, resulting in conduction band up-shift and a boost in Voc. Higher Voc with undiminished photocurrent is achieved with nitrate-hydrotalcite nanoclay gel electrolyte for organic as well as for inorganic dye (D35 and N719) systems. 10 % improvement in the efficiency for hydrotalcite clay gel electrolyte is obtained, compared to that of the liquid electrolyte. The power conversion efficiency can be achieved as high as 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.
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