Electronic Optimization of Heteroleptic Ru(II) Bipyridine Complexes by Remote Substituents: Synthesis, Characterization, and Application to Dye-Sensitized Solar Cells
作者:Won-Sik Han、Jung-Kyu Han、Hyun-Young Kim、Mi Jin Choi、Yong-Soo Kang、Chyongjin Pac、Sang Ook Kang
DOI:10.1021/ic101909e
日期:2011.4.18
We prepared a series of new heteroleptic ruthenium(II) complexes, Ru(NCS)(2)LL' (3a-3e), where L is 4,4'-di(hydroxycarbonyl)-2,2'-bipyridine and L' is 4,4'-di(p-X-phenyl)-2,2'-pyridine (x = CN (a), F (b), H (c), OMe (d), and NMe2 (e)), in an attempt to explore the structure activity relationships in their photophysical and electrochemical behavior and in their performance in dye-sensitized solar cells (DSSCs). When substituent X is changed from electron-donating NMe2 to electron-withdrawing CN, the absorption and emission maxima reveal systematic bathochromic shifts. The redox potentials of these dyes are also significantly influenced by X. The electronic properties of the dyes were theoretically analyzed using density functional theory calculations; the results show good correlations with the experimental results. The solar-cell performance of DSSCs based on dye-grafted nanocrystalline TiO2 using 3a-3e and standard N3 (bis[(4,4'-carboxy-2,2'-bipyridine)(thiocyanato)]ruthenium(II)) were compared, revealing substantial dependences on the dye structures, particularly on the remote substituent X. The 3d-based device showed the best performance: eta = 8.30%, J(SC) = 16.0 mA center dot cm(-2), V-OC = 717 mV, and ff = 0.72. These values are better than N3-based device.