Hindawi Publishing Corporation Journal of Chemistry Volume 2013, Article ID 910527, 5 pages http://dx.doi.org/10.1155/2013/910527 Research Article Improving the Spectral Response of Black Dye by Cosensitization with a Simple Indoline Based Dye in Dye-Sensitized Solar Cell Md. Akhtaruzzaman, 1 Ashraful Islam, 2 Mohammad Rezaul Karim, 3 A. K. Mahmud Hasan, 1 and Liyuan Han 2 1 Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia 2 Photovoltaic Materials Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan 3 Center of Excellence for Research in Engineering Materials (CEREM), College of Engineering, King Saud University, Riyadh 11421, Saudi Arabia Correspondence should be addressed to Md. Akhtaruzzaman; akhtar@um.edu.my Received 29 June 2012; Accepted 28 August 2012 Academic Editor: Ahmed El-Shafei Copyright © 2013 Md. Akhtaruzzaman et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Indoline dye D-1 was successfully applied as a cosensitizer for improving the spectral response of black dye in dye-sensitized solar cells (DSCs). It was observed that D-1 effectively increases the short-circuit photocurrent by offsetting the competitive light absorption by I/I 3 − electrolyte in the wavelength region 350–500nm when adsorbed on the TiO 2 nanocrystaline �lms in a mix dye system. e DSCs containing the D-1 and black dye achieved a power conversion efficiency of 9.80% with higher short-circuit photocurrent of 19.54 mA/cm 2 compared to the system of black dye without cosensitization under standard AM 1.5 sunlight. 1. Introduction Dye-sensitized solar cells (DSSC) based on nanocrystalline TiO 2 electrodes are promising candidate for low-cost alterna- tive energy sources compared to silicon and other inorganic semiconductor-based photovoltaic devices [1–5]. erefore, many researchers have continued their tremendous efforts over the last two decades for improving the performances of DSCs [6–9]. In DSCs, a sensitizing dye adsorbed at the surface of a wide band gap semiconductor (usually nanostructured TiO 2 ) absorbs light to transfer an electron to the semiconductor conduction band, followed by dye regeneration by a solution redox electrolyte or a solid hole conductor. e most common and efficient dyes employed so far in these solar cells are Ru(II) polypyridyl complexes as their intense charge-transfer (CT) absorption in the whole visible range, high quantum yield for the formation of the lowest CT excited state, and ease to tune redox properties [10–18]. e photoexcitation of the metal-to-ligand charge- transfer (MLCT) excited states of the adsorbed dye leads to an efficient injection of electrons into the conduction band of TiO 2 . Up to now, the highest conversion efficiency () from solar light to electric power for DSCs is over 11% under standard AM 1.5 conditions, which has been obtained from porous TiO 2 electrode using Ru polypyridine complexes (black dye) as sensitizers, and an organic electrolyte con- taining I − /I 3 − as a hole transport media [7]. However, the conversion efficiency of DSCs is still lower than that of the silicon-based photovoltaic cells. It will be required to improve the light harvesting efficiency in the near-IR region as well as over the entire visible region of the solar spectrum to further improve the conversion efficiency. Black dye based DSCs show a strong dip at about 380 nm in the incident photon-to-current conversion efficiency (IPCE) spectrum due to the competitive light absorption of the triiodide and black dye. To overcome this problem, recently a mix dyes system has been used to avoid the competitive adsorption and aggregation among dyes that may induce unfavorable charge or energy transfer and quenching of photo-excited states [8, 9]. Although the efficiency of black dye increased with the combination of an organic dye, the mechanism and selection of this dye in that system has yet to be clear.