Supplementary Materials

Flexible photoanodes of TiO2 particles and metallic single-walled carbon nanotubes for flexible dye-sensitized solar cells

Jiyong Leea†, Hosung Kangb†, Jae-Yeol Hwangc, Sung Wng Kima,c and Seunghyun Baik*c,d

a Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Koreab SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 440-746, Koreac Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 440-746, Republic of Korea. d School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746, Korea†These authors contributed equally to this work

*E-mail : sbaik@me.skku.ac.kr; Fax:+82-31-290-5889; Tel: +82-31-290-7456

Figure S1. High-resolution transmission electron microscopy images of M-SWNTs.

Figure S2. Raman spectra of M-SWNTs (a) and S-SWNTs (b). The excitation wavelengths were 514 and 785 nm. Metallic or semiconducting peak regions are designated [S1, S2]. The semiconducting peak was more apparent for S-SWNTs at 514 nm whereas the metallic peak was dominant for M-SWNTs at 785 nm.

Figure S3. Absorbance spectra of M-SWNTs (a) and S-SWNTs (b). Metallic and semiconducting peak regions are designated, and the spectra were normalized for comparison [S1, S3]. The purity of M-SWNTs (Nanointegris, IsoNanotubes-M) and S-SWNTs (Nanointegris, IsoNanotubes-S) specified in the technical data sheet was 95%.

Figure S4. Thermogravimetric analysis of a photoanode. The relative weight ratio between pure TiO2

particles and the photoanode composed of M-SWNTs and TiO2 particles was 100:98.8 at 600C. Therefore, the relative weight ratio of M-SWNTs in the photoanode was found to be 1.2% by thermogravimetric analysis. The relative weight ratio between M-SWNTs and TiO2 particles was 1:99 in the initial mixture for the fabrication of the photoanode.

M-SWNT weight concentration (%)

Jsc (mA/cm2) Voc (V) Fill Factor (%)

Efficiency(%)

3.5 1.2 0.48 42.1 0.24

1.3 3.2 0.49 45.3 0.70

1.0 4.4 0.52 46.5 1.1

Table S1. The photoanodes with different M-SWNT concentration were assembled for conventional sandwich-type front-illuminated DSCs for photovoltaic performance comparison. The SWNT-TiO2

photoanode was applied on an ITO-coated PET film. The fluorine-doped tin oxide (FTO)-coated glass (NSG; 8 ohm/sq) was used as a counter electrode. The two electrodes were combined by a plastic thin film spacer to have cavity for electrolyte filling. A detailed description about the fabrication process of conventional sandwich-type front-illuminated DSCs was published elsewhere [S4, S5, S6]. All the DSCs were characterized in flat condition.

Figure S5. Current-voltage characteristics of DSCs were investigated in flat condition as a function of the photoanode thickness. The thickness was controlled by multiple-transfer of the free standing SWNT-TiO2 film on the ITO-coated PET substrate. The corresponding thicknesses of 2, 3, and 4 layers were 8, 12, and 16 µm.

Figure S6. J-V characteristics of the conventional sandwich-type front-illuminated DSC characterized in flat condition. The photoanode was fabricated using pure TiO2 particles without nanotubes. A detailed description about the fabrication process of conventional sandwich-type front-illuminated DSCs was published elsewhere [S4, S5, S6]. Briefly, the FTO glass was pretreated by 40 mM TiCl 4

solution followed by the application of TiO2 paste and annealing (500 C for 2 hours). The thickness

of the TiO2 layer was 12 m. The working electrode was then immersed in N-719 solution (0.5 mM in ethanol) for 24 hours. The platinum-sputtered FTO glass was used as a counter electrode. Finally, the sandwich-type cell was fabricated by combining the working electrode and counter electrode using a hot-melted plastic spacer film. The electrolyte was introduced into the cavity by the vacuum filling method [S4, S5, S6].

Figure S7. The EIS characterization of the front-illuminated DSC with the M-SWNTs/TiO2

photoanode. The optical images of the DSC are provided with the corresponding bending radius. The real part range of each semicircle in Nyquist plot indicates the corresponding resistance. The sum of Rh and R1 increased as the photoanode was bent from the flat status to the bending radius of 5 mm. It

is difficult to isolate the shunt resistance from the EIS data since R2 is affected by shunt resistance, charge transfer within the photoanode, and charge transfer at the interface [S6, S7, S8].

Figure S8. Normalized efficiency as a function of the photoanode thickness. The bending radius was 5 mm.

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