1

Supporting Information

Improving Performance via Blocking Layers in Dye-Sensitized Solar Cells

Based on Nanowire Photoanodes

Luping Li,1* Cheng Xu,2 Yang Zhao,1 Shikai Chen,1 and Kirk J. Ziegler1,2*

1 Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 2 Department of Materials Science & Engineering, University of Florida, Gainesville, Florida 32611 * Corresponding author. Email address: kziegler@che.ufl.edu (K. Ziegler); lupingli@ufl.edu (L.

Li)

2

Figure S1 shows the TEM images of nanowires with different thicknesses of the porous

TiO2 coating on the HfO2 blocking layer. These nanowires were used as the photoanode for

DSSCs. Different TiO2 thicknesses were shown to impact dye loading and device performances

(see Figure 4 and Table 2 of main text).

Figure S1: TEM images of ITO nanowires with TiO2 coatings with a thickness of (a) 45; (b) 70; and (c) 90 nm.

Figure S2: UV-vis spectra of dye desorbed in 0.1 M NaOH water/ethanol (1:1 v/v) solution from

nanowire photoanodes.

3

Figure S2 shows the UV-vis spectra of the desorbed dye solutions from the nanowire

photoanodes. The photoanodes were soaked in a 0.1 M NaOH water/ethanol (1:1 v/v) solution

for 2 h to desorb the dye. The amount of dye adsorbed onto TiO2 shell increases with the

thickness of the TiO2 shell. Note that the concentration of dye is similar for the same porous

shell thickness regardless of the composition of the compact layer.

100

101

102

103

104

105

0

5

10

15

20

25

HfO2 ALD

TiO2 ALD

Ph

as

e (

De

g.)

Frequency (Hz)

Figure S3: Bode phase plot for the cells with HfO2 or TiO2 ALD layers between ITO nanowires and porous TiO2 shell. EIS were performed in open circuit conditions under AM 1.5 illumination.

Figure S3 shows a Bode phase plot for the cells with HfO2 or TiO2 ALD layers between

ITO nanowires and porous TiO2 shell. EIS measurements were performed at open circuit

conditions under AM 1.5 illumination. On a Bode phase plot of a DSSC, typically three

characteristic peaks are observed:1 (a) a high frequency peak (kHz range) representing charge

transport at the Pt counter electrode; (b) a medium frequency peak (10-100 Hz range)

representing charge transport in TiO2; and (c) a low frequency peak (mHz range) representing

the Nernstian diffusion in the electrolyte (not shown). Electron lifetime can be calculated using

4

τ=(2·π·fpeak)-1, where fpeak represents the peak frequency in a Bode phase plot. Using the peaks

centered around 10 Hz in Figure S3, the electron lifetime is calculated to be 0.025 and 0.012 s

for devices with HfO2 and TiO2 blocking layers, respectively. These results are in agreement

with the electron lifetime obtained from OCVD measurement presented in Figure 8.

References

(1) Kern, R.; Sastrawan, R.; Ferber, J.; Stangl, R.; Luther, J., Modeling and Interpretation of

Electrical Impedance Spectra of Dye Solar Cells Operated under Open-Circuit Conditions.

Electrochim. Acta 2002, 47, 4213-4225.