Nakade Shogo, Makimoto Yohei, Kubo Wataru, Kitamura Takayuki, Wada Yuji, Yanagida Shozo
Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
J Phys Chem B. 2005 Mar 3;109(8):3488-93. doi: 10.1021/jp046002d.
Dye-sensitized solar cells (DSC) were prepared from nanoporous TiO(2) electrodes with two different cobalt complex redox couples, propylene-1,2-bis(o-iminobenzylideneaminato)cobalt(II) {Co(II)(abpn)} and tris(4,4'-di-tert-buthyl-2,2'-bipyridine)cobalt(II) diperchlorate {Co(II)(dtb-bpy)(3)(ClO(4))(2)}. The performances of the DSCs were examined with varying the concentrations of the redox couples and Li cations in methoxyacetonitrile. Under 1 sun conditions, short-circuit currents (J(sc)) increased with the increase of the redox couple concentration, and the maximum J(sc) was found at the Li(+) concentration of 100 mM. To rationalize the observed trends of J(sc), electron diffusion coefficients and lifetimes in the DSCs were measured. Electron diffusion coefficients in the DSCs using cobalt complexes were comparable to the previously reported values of nanoporous TiO(2). Electron lifetime was independent of the concentration of the redox couples when the concentration ratio of Co(II)(L) and Co(III)(L) was fixed. With the increase of Li(+) concentration, the electron lifetime increased. These results were interpreted as due to their slow charge-transfer kinetics and the cationic nature of Co complex redox couples, in contrast to the anionic redox couple of I(-)/I(3)(-). The increase of the lifetimes with Li(+) was interpreted with the decrease of the local concentration of Co(III) near the surface of TiO(2). The addition of 4-tert-butylpyridine (tBP) with the presence of Li(+) increased J(sc) significantly. The observed increase of the electron lifetime by tBP could not explain the large increase of J(sc), implying that tBP facilitates the charge transfer from Co(II)(L) to dye cation, with the association of the change of the reorganization energy between Co(II) and Co(III).
采用具有两种不同钴配合物氧化还原对的纳米多孔TiO₂电极制备了染料敏化太阳能电池（DSC），这两种氧化还原对分别是丙烯-1,2-双（邻亚氨基苄叉氨基）钴（II）{Co(II)(abpn)}和三（4,4'-二叔丁基-2,2'-联吡啶）钴（II）高氯酸二水合物{Co(II)(dtb-bpy)₃(ClO₄)₂}。在甲氧基乙腈中，通过改变氧化还原对和Li⁺阳离子的浓度来考察DSC的性能。在1个太阳光照条件下，短路电流（Jsc）随着氧化还原对浓度的增加而增大，且在Li⁺浓度为100 mM时发现最大Jsc。为了合理解释观察到的Jsc趋势，测量了DSC中的电子扩散系数和寿命。使用钴配合物的DSC中的电子扩散系数与先前报道的纳米多孔TiO₂的值相当。当Co(II)(L)和Co(III)(L)的浓度比固定时，电子寿命与氧化还原对的浓度无关。随着Li⁺浓度的增加，电子寿命增加。这些结果被解释为是由于它们缓慢的电荷转移动力学以及钴配合物氧化还原对的阳离子性质，这与I⁻/I₃⁻的阴离子氧化还原对形成对比。Li⁺导致寿命增加被解释为TiO₂表面附近Co(III)的局部浓度降低。在Li⁺存在下添加4-叔丁基吡啶（tBP）显著提高了Jsc。观察到的tBP使电子寿命增加并不能解释Jsc的大幅增加，这意味着tBP促进了从Co(II)(L)到染料阳离子的电荷转移，同时伴随着Co(II)和Co(III)之间重组能的变化。
