title: Nanoclay gelation approach toward improved dye-sensitized solar cell efficiencies: an investigation of charge transport and shift in the TiO2 conduction band.
abstract: 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 TiO(2)/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]:[I(2)] = 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 TiO(2)/electrolyte interface, resulting in an upward shift in the conduction band and a boost in open-circuit voltage (V(OC)). Higher V(OC) 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.
authors.affiliation: School of Materials Science & Engineering, Nanyang Technological University, Block N4.1 Nanyang Avenue, Singapore 639798.
authors.forename: Xiu
authors.initials: X
authors.lastname: Wang
authors.forename: Sneha A
authors.initials: SA
authors.lastname: Kulkarni
authors.forename: Bruno Ieiri
authors.initials: BI
authors.lastname: Ito
authors.forename: Sudip K
authors.initials: SK
authors.lastname: Batabyal
authors.forename: Kazuteru
authors.initials: K
authors.lastname: Nonomura
authors.forename: Chee Cheong
authors.initials: CC
authors.lastname: Wong
authors.forename: Michael
authors.initials: M
authors.lastname: Grätzel
authors.forename: Subodh G
authors.initials: SG
authors.lastname: Mhaisalkar
authors.forename: Satoshi
authors.initials: S
authors.lastname: Uchida