Among various solar cell technologies, dye sensitized solar cells (DSSCs) have attracted widespread commercial and academic interest due to their relatively high efficiency and low production cost [1-5].

In DSSCs, dye molecules undergo optical excitation, followed by rapid electron transfer to TiO2.  The ionized dye molecules are then reduced by iodide ions (I) in the electrolyte, which form triiodide ions (I3). The counter electrode uses electrons that flow from the photoelectrode, through the external circuit, to reduce triiodide ions back to iodide, completing the cycle [6, 7].

The dye sensitizer plays a critical role in the light harvesting. Recently, the highest power conversion efficiency of DSSCs based on the Zn-complex dye has achieved 12.3% [8]. But typically ruthenium based complexes are well known to get higher efficiencies. Ruthenium is a rare and potentially toxic heavy metal and ruthenium complexes are expensive. So, there is a need to develop new precious metal-free dye sensitizers that can replace the traditional ruthenium sensitizer. In recent years, organic dyes have attracted lot of researchers because of their variety of molecular structures, high molar extinction coefficient, low cost and simple and environmentally friendly preparation process. In the last decade, many investigations on p-conjugated molecules with donor–acceptor moieties, such as oligothiophene [9], indoline [10], triphenylamine [11] and coumarin [12] have been conducted.

To catalyze the triiodide reduction reaction, platinum is typically used [13, 14].  The high cost and limited availability of platinum is not compatible with a low-cost sustainable technology.  Therefore, researches have been investigating various alternative catalysts, including cobalt sulfide [15-18], carbon black [19-21], graphite [22, 23], graphene [24, 25], and carbon nanotubes [26].

Researchers are also investigating the possibility of fabricating DSSCs on low-cost substrates, instead of transparent conducting oxide (TCO). Typically the TCO is a fluorine-doped tin oxide (FTO), which accounts for approximately 50% of the total cost of DSSCs [27]. Also, these substrates have several advantages over TCO, i.e., low weight, bendability, portability, and high strength. Conductive substrates such as indium tin oxide (ITO)-coated polyethylene terephthalate (PET) film [28], ITO-coated polyethylene naphthalate (ITO-PEN) film [29], composite structure consisting of electrospun polyvinylidene fluoride (PVDF) polymer nanofibers and TiO2 nanoparticles [30] have been reported.

With these advancements, it is possible that DSSCs will be good competitors to their rivals in the future.

-Hafeez Anwar

 

References

1. Brian, O.; Graetzel, M., A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature (London) 1991, 353, 737-740.

2. Asbury, J. B.; Ellingson, R. J.; Ghosh, H. N.; Ferrere, S.; Nozik, A. J.; Lian, T. Q., Femtosecond IR study of excited-state relaxation and electron-injection dynamics of Ru(dcbpy)(2)(NCS)(2) in solution and on nanocrystalline TiO2 and Al2O3 thin films. J Phys Chem B 1999, 103 (16), 3110-3119.

3. Peter, L.M.;Wijayantha K.G.U., Electron transport and back reaction in dye sensitised nanocrystalline photovoltaic cells. Electrochimica Acta 2000, 45 4543–4551.

4. Heimer, T. A.; Heilweil, E. J.; Bignozzi, C. A.; Meyer, G. J., Electron injection, recombination, and halide oxidation dynamics at dye-sensitized metal oxide interfaces. J. Phys. Chem. A 2000, 104 (18), 4256-4262.

5. Gratzel, M., Photoelectrochemical cells. Nature (London) 2001, 414, 338-344.

6. Park, N. G.; Kang, M. G.; Kim, K. M.; Ryu, K. S.; Chang, S. H.; Kim, D. K.; van de Lagemaat, J.; Benkstein, K. D.; Frank, A. J., Morphological and photoelectrochemical characterization of core-shell nanoparticle films for dye-sensitized solar cells: Zn-O type shell on SnO2 and TiO2 cores. Langmuir 2004, 20 (10), 4246-4253.

7. Lee, J. J.; Coia, G. M.; Lewis, N. S., Current density versus potential characteristics of dye-sensitized nanostructured semiconductor photoelectrodes. 1. Analytical expressions. J Phys Chem B 2004, 108 (17), 5269-5281.

8. A. Yella, H. W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. Nazeeruddin, E. W. Diau, C. Y. Yeh, S. M. Zakeeruddin and M. Gratzel, Science, 2011, 334, 629.

9. Liao, Kung-Ching; Anwar, Hafeez; Hill, Ian; Vertelov, Grigory; Schwartz, Jeffrey. Comparative Interface Metrics for Metal-Free Monolayer-Based Dye-Sensitized Solar Cells. Applied Materials & Interfaces. Accepted for publication (November 9, 2012).

10. S. Ito, H. Miura, S. Uchida, M. Takata, K. Sumioka, P. Liska, P. Comte, P. Pechy and M. Gr€atzel, Chem. Commun., 2008, 5194.

11. S. Hwang, J. H. Lee, C. Park, H. Lee, C. Kim, C. Park, M. H. Lee,W. Lee, J. Park, K. Kim, N. G. Park and C. Kim, Chem. Commun., 2007, 4887.

12. Z. S. Wang, Y. Cui, K. Hara, Y. Dan-oh, C. Kasada and A. Shinpo, Adv. Mater., 2007, 19, 1138.

13. Papageorgiou, N., Counter-electrode function in nanocrystalline photoelectrochemical cell configurations. Coordin Chem Rev 2004, 248 (13-14), 1421-1446.

14. Yoo, B.; Lim, M. K.; Kim, K.-J., Application of Pt sputter-deposited counter electrodes based on micro-patterned ITO glass to quasi-solid state dye-sensitized solar cells. Current Applied Physics 2012, 12 (5), 1302-1306.

15. Wang, M.; Anghel, A. M.; Marsan, B. t.; Cevey Ha, N.-L.; Pootrakulchote, N.; Zakeeruddin, S. M.; Grätzel, M., CoS Supersedes Pt as Efficient Electrocatalyst for Triiodide Reduction in Dye-Sensitized Solar Cells. Journal of the American Chemical Society 2009, 131 (44), 15976-15977.

16. Lin, J.-Y.; Liao, J.-H.; Chou, S.-W., Cathodic electrodeposition of highly porous cobalt sulfide counter electrodes for dye-sensitized solar cells. Electrochimica Acta 2011, 56 (24), 8818-8826.

17. Lin, J.-Y.; Liao, J.-H.; Wei, T.-C., Honeycomb-like CoS Counter Electrodes for Transparent Dye-Sensitized Solar Cells. Electrochemical and Solid-State Letters 2011, 14 (4), D41-D44.

18. Lin, J.-Y., Mesoporous Electrodeposited-CoS Film as a Counter Electrode Catalyst in Dye-Sensitized Solar Cells. Journal of The Electrochemical Society 2012, 159 (2), D65.

19. Murakami, T. N.; Ito, S.; Wang, Q.; Nazeeruddin, M. K.; Bessho, T.; Cesar, I.; Liska, P.; Humphry-Baker, R.; Comte, P.; Pechy, P.; Gratzel, M., Highly Efficient Dye-Sensitized Solar Cells Based on Carbon Black Counter Electrodes. Journal of The Electrochemical Society 2006, 153 (12), A2255-A2261.

20. Murakami, T. N.; Grätzel, M., Counter electrodes for DSC: Application of functional materials as catalysts. Inorganica Chimica Acta 2008, 361 (3), 572-580.

21. Li, P.; Wu, J.; Lin, J.; Huang, M.; Huang, Y.; Li, Q., High-performance and low platinum loading Pt/Carbon black counter electrode for dye-sensitized solar cells. Solar Energy 2009, 83 (6), 845-849.

22. Acharya, K. P.; Khatri, H.; Marsillac, S.; Ullrich, B.; Anzenbacher, P.; Zamkov, M., Pulsed laser deposition of graphite counter electrodes for dye-sensitized solar cells. Appl. Phys. Lett. 2010, 97 (20).

23. Veerappan, G.; Bojan, K.; Rhee, S.-W., Sub-micrometer-sized Graphite As a Conducting and Catalytic Counter Electrode for Dye-sensitized Solar Cells. ACS Applied Materials & Interfaces 2011, 3 (3), 857-862.

24. Wang, X.; Zhi, L.; Mullen, K., Transparent, Conductive Graphene Electrodes for Dye-Sensitized Solar Cells. Nano Letters 2007, 8 (1), 323-327.

25. Guai, G. H.; Song, Q. L.; Guo, C. X.; Lu, Z. S.; Chen, T.; Ng, C. M.; Li, C. M., Graphene- counter electrode to significantly reduce Pt loading and enhance charge transfer for high performance dye-sensitized solar cell. Solar Energy 2012, 86 (7), 2041-2048.

26. Anwar, Hafeez; George, Andrew.E.;Hill, Ian. Vertically-aligned carbon nanotube counter electrodes for dye-sensitized solar cells. Solar Energy. Accepted for publication (November 20, 2012).

27. Yen, Chuan-Yu, Shu-Hang Liao, Min-Chien Hsiao, Cheng-Chih Weng, Yu-Feng Lin, Chen-Chi M. Ma, Ming-Chi Tsai, Ay Su, Kuan-Ku Ho, and Po-Lan Liu. “A Novel Carbon-based Nanocomposite Plate as a Counter Electrode for Dye-sensitized Solar Cells.” Composites Science and Technology. 2009, 69(13), 2193–2197.

28. M.D¨ urr, A.Schmid,M.Obermaier,S.Rosselli,A.Yasuda,G.Nelles,Low- temperature fabricationofdye-sensitizedsolarcellsbytransferofcomposite porous layers,NatureMater.4(2005)607–611.

29. T. Miyasaka, M. Ikegami, Y. Kijitori, Photovoltaic performance of plastic dye- sensitized electrodes prepared by low-temperature binder-free coating of mesoscopic titania, J. Electrochem. Soc. 154 (2007) A455–A461.

30. Yuelong Li,ab Doh-Kwon Lee,a Jin Young Kim,a BongSoo Kim,a Nam-Gyu Park,c Kyungkon Kim,d

Joong-Ho Shin,e In-Suk Choi*e and Min Jae Ko*.Highly durable and flexible dye-sensitized solar cells fabricated on plasticsubstrates: PVDF-nanofiber-reinforced TiO2 photoelectrodes. Energy Environ. Sci., 2012, 5, 8950.

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