In order to modify the pore morphology of TiO2 (pore size, surface area, and porosity) to improve the DSSC performance, solvents and PEG in different molecular weights and loadings were added to TiO2 paste, in addition to using different PEG burn out rate after TiO2 films coating. In specific, TiO2 films with different pore morphology were prepared by coating commercial TiO2 nanoparticles (P25) and a scattering layer on FTO conducting glass using doctor-blade technique. The surface area, porosity, and pore size of TiO2 films and the photochemical characteristics of DSSCs with these TiO2 films have been examined by SEM, BET, and EIS analysis.
Results showed that PEG addition could separate the TiO2 particles leading to modify the pore morphology of TiO2. In butanol based solvent, the surface area, pore size and porosity of TiO2 film only increased slightly because butanol is a poor solvent for PEG, and PEG molecules tend to curl in a poor solvent. Even changed the molecular weights, there was almost no difference of molecule sizes in the TiO2 paste.
When the solvent was changed from butanol to water, the average pore size was increased from 11.8 nm to 22 nm due to the large solubility of PEG leading full PEG chain extension in the TiO2 particle matrix. And the molecular weights adjusting in water solution increased the pore size from 22 nm for 35k PEG to 30.5 nm for 100k PEG. Because the PEG porogen (pore generator) in good solvent (water) leading the polymer chains of PEG tend to extend well, as the PEG polymer chains are fully extended in water-based TiO2 paste, higher molecular weight shall lead to larger polymer coil size.
In addition to using different solvents and molecular weights of PEG, burn out rate is another issue to modify the pore morphology of TiO2. When an additional
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isothermal bake at 100oC the average pore size increased due to the expansion of PEG polymer chains and possibly some degree of PEG chain aggregation. In contrast, PEG chains were decomposed readily without enough time for chain extension. This yielded smaller pore size (11.8 nm for 35K PEG in butanol system, or 22.0 nm for 35k PEG in water system) under a fast burn-out rate at 400oC.
Applying these pore morphology modified TiO2 films to DSSCs. By PEG addition, the conversion efficiency of DSSC increased with increasing pore size because electrolyte diffuse more easily in large pore size TiO2 films led to faster dye regeneration, and the electron transport resistance in the TiO2/dye/electrolyte interface (R2) and the resistance (R3) of Nernstian diffusion decreased. In this study, the best conversion efficiency of DSSC reached 5.13% with open circuit voltage 0.73V and short circuit current density 13.07mA/cm2. TiO2 electrode of this DSSC was prepared by 15% 35k PEG loading TiO2 paste in water system and the average pore size was 22 nm.
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Reference
[1] M. Grätzel, Nature, 414, 338 (2001)
[2] 李佳徽, “ Synthesis of Pt/Ni Bimetallic Nanoparticles and Its Application in Dye-Sensitized Solar Cells”, National Tsing Hua University, master thesis (2008) [3] Newport Corporation Website
[4] B. O’Regan and M. Grätzel, Nature, 353, 737 (1991) [5] M. Grätzel, J. Photochem. Photobiol. A, 164, 3 (2004) [6] M. Grätzel, Prog. Photovoltaics, 14, 429 (2006)
[7] Q. Shen and T. Toyoda, Thin Solid Films 167 438 (2003)
[8] S. Ngamsinlapasathian, S. Sakulkhaemaruethai, S. Pavasupree, A. Kitiyanan, T.
Sreethawong, Y. Suzuki, and S. Yoshikawa, J. Photochem. Photobiol. A164, 145 (2004)
[15] M. Grätzal, Curr. Opin. Colloid Interface Sci., 4, 314 (1999) [16] J. R. Durrant and S. A. Haque, Nature Mat., 2, 362 (2003) [17] M. Grätzel, Prog. Photovolt. Res. Appl., 8, 171 (2000)
81
[18] T. Miyasala and Y. Kijitori, J. Electrochem. Soc., 151, A1767 (2004) [19] M. Grätzel, MRS Bull., 30, 23 (2005)
[20] C. J. Barbe, F. Arendse, P. Comte, M. Jirousek, F. Lenzmann, V. Shklover, and M.
Grätzel, J. Am. Ceram. Soc., 80, 3157 (1997)
[21] K. Kalyanasundaram and M. Grätzel, Coord. Chem. Rev., 77 (1998)
[22] M. K. Nazeeruddin, A. Kay, I. Rodicio, R. Humphrybaker, E. Muller, P. Liaka, N.
Vlachopoulos, and M. Gratzel, J. Am. Ceram. Soc., 115, 6382 (1993) [23] G. P. Smestad and M. Grätzel, J. Chem. Educ., 75, 752 (1998)
[24] D.S. Tsoukleris, I. M. Arabatzis, E. Chatzivasiloglou, A. I. Kontos, V. Belessi, M.
C. Bernard, and P. Flaras, Sol. Energy, 79, 422 (2005)
[25] S. Karuppuchamy, K. Nonomura, T. Yoshida, T. Sugiura, and H. Minoura, Solid State Ion., 151, 19 (2002)
[26] S. Karuppuchamy, D. P. Amalnerkar, K. Yamaguchi, T. Yoshida, T. Sugiura, and H. Minoura, Chem. Lett., 78 (2001)
[27] M. S. wong, T. S. Yang, and C. B. Shiu, Surf. Sci., 548, 75 (2004)
[28] S. B. Amor, G. Baud, J. P. Besse, and M. Jacquet, Thin Solid Films, 293, 163 (1997)
[29] M. Gomez, E. Magnusson, E. Olsson, A. Hagfeldt, S. E. Lindquist, and C. G.
Granquiat, Sol. Energy Mater. Sol. Cells, 62, 269 (2000) [30] D. Dumitriu, Appl. Catal. B-Environ., 25, 83 (2000) [31] K. Okimura, Surf. Coat. Technol., 135, 186 (2001)
[32] P. Zeman and S. Takabayashi, Surf. Coat. Technol., 153, 93 (2002) [33] D. Byun, J. Hazard. Mater., 73, 199 (2000)
[34] D. R. Burgess, P. A. Morris, T. J. Anderson, and J. L. Hohman, J. Cryst. Growth, 166, 763 (1999)
[35] M. Paulose, K. Shankar, O. K. Varghese, G. K. Mor, and C. A. Grimes, J. Phys.
82
D: Appl. Phys., 39, 2498 (2006)
[36] B. Tan and Y. Y. Wu, J. Phys. Chem. B, 110, 15932 (2006) [37] Solaronix Website
[38] M. Grätzel, Inorg. Chem., 44, 6841 (2005)
[39] T. Naoki and Y. Wang, Langmuir, 10, 4574 (1994)
[40] S. R. Brankovic, J. McBreen, and R. R. Adzic, Surf. Sci., 479, L363 (2001) [41] A. Kay and M. Grätzel, Sol. Energy Mater. Sol. Cells, 44, 99 (1996)
[42] S. Cherian and C. C. Wamser, J. Phys. Chem. B, 104, 3624 (2000)
[43] J. Hagen, W. Schaffrath, P. Otschik, R. Fink, A. Bacher, H. W. Schmidt, and D.
Haarer, Synth. Met., 89, 215 (1997)
[44] Y. X. Li, J. Hagen, W. Schaffrath, P. Otschik, and D. Haarer, Sol. Energy Mater.
Sol. Cells, 56, 167 (1999)
Gerhard, S. Himmler, and P. Wasserscheid, Solid State Ion., 177, 3141 (2006) [48] P. Wang, S. M. Zakeeruddin, J. E. Moser, M. K. Nazeeruddin, T. Sekiguchi, and
M. Grätzel, Nature Mate., 2, 498 (2003)
83
[52] W. Kubo, K. Murakoshi, T. Kitamura, S. Yoshida, M. Haruki, K. Hanabusa, H.
Shirai, Y. Wada, and S. Yanagida, J. Phys. Chem. B, 105, 12809 (2001)
[53] R. Kawano, H. Matsui, C. Matsuyama, A. Sato, M. Susan, N. Tanabe, and M.
[57] N. Papageorgiou, Coord. Chem. Rev., 248, 1421 (2004)
[58] Y. Chiba, A. Islam, Y. Watanabe, R. Komiya, N. Koide, and L. Y. Han, Japanese J. Appl. Phys. Part 2-Letters & Express Letters, 45, L638 (2006)
[59] T. C. Wei, C. C. Wan, and Y. Y. Wang, J. Phys. Chem. C, 111, 4847 (2007) [60] T. C. Wei, C. C. Wan, and Y. Y. Wang, Appl. Phys. Lett., 88, 103122 (2006) [61] Y. Saito, W. Kubo, T. Kitamura, Y. Wada, and S. Yanagida, J. Photochem.
Photobiol. A-Chem., 164, 153 (2004)
[62] Y. Saito, T. Kitamura, Y. Wada, and S. Yanagida, Chem. Lett., 31, 1060 (2002) [63] E. Ramasamy, W. J. Lee, D. Y. Lee, and J. S. Song, Appl. Phys. Lett., 90,
173103 (2007)
[64] K. Imoto, K. Takahashi, T. Yamaguchi, T. Komura, J. Nakamura, and K. Murata, Sol. Energy Mater. Sol. Cells, 79, 459 (2003)
[65] R. Kikuchi, T. Hoshikawa, and K. Eguchi, J. Electroanal. Chem., 588, 59 (2006) [66] K. Suzuki, M. Yamaguchi, M. Kumagai, and S. Yanagida, Chem. Lett., 32, 28
(2003)
[67] T. Kitamura, M. Maitani, M. Matsuda, Y. Wada, and S. Yanagida, Chem. Lett.,
84
1054 (2001)
[68] N. Ikeda, K. Teshima and T. Miyasaka, Chem. Commun., 1733 (2006)
[69] S. Ito, N. L. C. Ha, G. Rothenberger, P. Liska, P. Comte, S. M. Zakeeruddin, P.
Pechy, M. K. Nazeeruddin, and M. Grätzel, Chem. Commun., 38, 4004 (2006) [70] P. M. Sommeling, B. C. O'Regan, R. R. Haswell, H. J. P. Smit, N. J. Bakker, J. J.
T. Smits, J. M. Kroon, and J. A. M. van Roosmalen, J. Phys. Chem. B, 110, 19191 (2006)
[71] N. G. Park, G. Schlichthorl, J. van de Lagemaat, H. M. Cheong, A. Mascarenhas, and A. J. Frank, J. Phys. Chem. B, 103, 3308 (1999)
[72] L. Y. Zeng, S. Y. Dai, K. J. Wang, X. Pan, C. W. Shi, and L. Guo, Chin. Phys.
Lett., 21, 1835 (2004)
[73] S. Ito, P. Liska, P. Comte, R. L. Charvet, P. Pechy, U. Bach, L. Schmidt-Mende, S. M. Zakeeruddin, A. Kay, M. K. Nazeeruddin, and M. Grätzel, Chem.
Commun., 41, 4351 (2005)
[74] S. Hore and R. Kern, Appl. Phys. Lett., 87, 263504 (2005)
[75] T. Miyasaka, M. Ikegami, and Y. Kijitori, J. Electrochem. Soc., 154 A455 (2007) [76] S. H. Kang, J.-Y. Kim, H. S. Kim, H.-D. Koh, J.-S. Lee, and Y.-E. Sung, J.
85
[81] L. Hu, S. Dai, J. Weng, S. Xiao, Y. Sui, Y. Huang, S. Chen, F. Kong, X. Pan, L.
Liang, and K. Wang, J. Phys. Chem. B, 111, 358 (2007)
[82] L. Zhao, J. Yu, J. Fan, P. Zhai, and S. Wang, Electrochem. Commun., 11, 2052 (2009)
[83] C. N. Rao, B.C. Satishkumar, A. Govindaraj, E. M. Vogl, and L. Basumallick, J.
Mater. Res., 12, 604 (1997)
[84] H. C. Zeng, S. M. Liu, L. M. Gan, L. H. Liu, and W. D. Zhang, Chem. Mater., 14, 1391 (2002)
[85] Y. Bando, M. Zhang, and K. Wada, J. Mater. Sci. Lett., 20 167 (2001)
[86] H. Imai, Y. Takei, K. Shimizu, M. Matsuda, and H. Hirashima, J. Mater. Chem., 9, 2971 (1999)
[94] Y. Saito, S. Kambe, T. Kitamura, Y. Wada, and S. Yanagida, Sol. Energy Mater.
Sol. Cells 83, 1 (2004)
86
[95] K. M. Lee, V. Suryanarayanan, and K. C. Ho, Sol. Energy Mater. Sol. Cells, 90, 2398 (2006)
[96] K. M. Lee, C. Y. Hsu, W. H. Chiu, M. C. Tsui, Y. L. Tung, S. Y. Tsai, and K. C.
Ho, Sol. Energy Mater. Sol. Cells, 93 2003 (2009)
[97] Y. H. Lai, C. Y. Lin, J. G. Chen, C. C. Wang, K. C. Huang, K. Y. Liu, K. F. Lin, J. J. Lin, and K. C. Ho, Sol. Energy Mater. Sol. Cells, 94, 668 (2010)
[98] S. Brunauer, P. H. Emmett, and E. Teller, J. Am. Chem. Soc., 60, 309 (1938) [99] R. B. Andersoann and W. K. Hall, J. Am. Chem. Soc., 70, 1727 (1984)
[100] J. Jagiello, M. Thommes, J. Jagiello, and M. Thommes, Carbon 42, 1227 (2004) [101] F. Kremer, A. Schonhals, and W. Luck, Broadband Dielectric Spectroscopy,
Springer-Verlag, Berlin Germany, 2002
[102] A. M. Sidorovich, Ukrainian Physical Journal, 29, 8, 1175 (1984) [103] A. R. Hippel, Dielectrics and Wave, John Willey & Sons, N. Y., 1954
[104] A. A. Volkov and A. S. Prokhorov, Radiophys. Quantum Electron., 46, 657 (2003)
[105] D. Kim, P. Roy, K. Lee, and P. Schmuki, Electrochem. Commun., 12, 574 (2010)
[106] Y. Chen, E. Stathatos, and D. D. Dionysiou, J. Photochem. Photobiol. A-Chem., 203, 192 (2009)
[107] S. Kang, J.-S. Yu, M. Kruk, and M. Jaroniec, Chem. Commun., 38, 1670 (2002) [108] J. Jiu, F. Wang, M. Sakamoto, J. Takao, and M. Adachi, Sol. Energy Mater. Sol.
Cells 87, 77 (2005)
[109] K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti, J.
Rouquerol, T. Siemieniewska, Pure Appl. Chem., 57, 603 (1985) [110] The University of Southern Maine, O=CHem Directory, Solvents [111] E. E. Dormidontova, Macromolecules, 37, 7747 (2004)