Thin Nanostructured Crystalline TiO₂ Films Templated by Block-copolymer and their Applications in dye-sensitized Solar Cells
Yajun Cheng^1┼, Jiaoli Li^1╪, Sebastian lenz¹, Mine Memesa¹, Sebastian Nett¹, Sebastian Emmerling¹, and Jochen. S. Gutmann^{1, 2}

1. Max-Planck Institute for Polymer Research, Mainz, Germany. ┼ Current address: Biomaterials group, polymer division, National Institute of Standards and Technology, Gaithersburg, MD, USA

╪ Current address: Organic Opto-electronics Lab, Department of Chemistry, Tsinghua University, Beijing, P. R. China 2. Inst. of. Physical Chemistry, University of Mainz, Mainz, Germany

Thin TiO₂ films showing rich morphologies are achieved by using sol-gel chemistry coupled with an amphiphilic polystyrene-block-poly (ethylene oxide) (PS-b-PEO) diblock copolymer as a structure-directing agent. The block copolymer undergoes a good-poor-solvent pair induced phase separation in a mixed solution of 1, 4-dioxane, concentrated hydrochloric acid (HCl) and Titanium tetraisopropoxide (TTIP). The morphologies of the titania-block copolymer composite films can be tuned by two different ways: Varying the weight fractions among 1, 4-dioxane, HCl, and TTIP with fixed copolymer concentration of 1.0 wt. % and changing the copolymer concentration with fixed weight fractions among 1, 4-dioxane, HCl, and TTIP. Through calcination the amorphous titania composite films can be converted to crystalline anatase phase. The local film structures are characterized by imaging analysis, for example, Scanning Electron Microscopy (SEM) and correspondingly, the long range lateral structures are measured by Grazing Incidence Small Angle X-ray Scattering (GISAX), as exhibited in Figure 1. On the basis of the morphology control, TiO₂ films of different morphologies are incorporated into hybrid dye-sensitized solar cells as the electron transport layers. By changing the morphology the performance of the solar cells can be tuned and the performance-morphology relationship of TiO₂ films is investigated.

Figure1. SEM images and 2D GISAXS images (insets, unit of q_y: Å^-1) of the crystalline TiO₂ thin films with different morphologies tuned by a series of PS-b-PEO concentrations in 1, 4-dioxane (From left to right: 0.25 wt. %, 0.50 wt. %, and 1.0 wt. %) with the weight fractions as following: W_{1, 4-dioxane}, 0.964, W_HCl, 0.007 and W_TTIP, 0.029.

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Name: Yajun Cheng

Mentor’s name: Sheng Lin-Gibson

Division: Polymers (854)

Laboratory: Materials Science and Engineering

Room and Building: B106, Bldg. 224

Mail Stop: 8543

Telephone: (301) 975 5520

FAX: (301) 975 4977

E-mail: yajun.cheng@nist.gov

Sigma Xi member: No

Category: Materials