Improving the photoresponse of copper(i) dyes in dye-sensitized solar cells by tuning ancillary and anchoring ligand modules
作者:Biljana Bozic-Weber、Sven Y. Brauchli、Edwin C. Constable、Sebastian O. Fürer、Catherine E. Housecroft、Frederik J. Malzner、Iain A. Wright、Jennifer A. Zampese
DOI:10.1039/c3dt51416a
日期:——
The syntheses of five homoleptic copper(I) complexes [CuL2][PF6] are described in which L is a 4,4′-di(4-bromophenyl)-6,6′-dialkyl-2,2′-bipyridine ligand (compounds 1–4 with methyl, nbutyl, isobutyl and hexyl substituents, respectively) or 4,4′-di(4-bromophenyl)-6,6′-diphenyl-2,2′-bipyridine (5). The new ligands 2–5 and copper(I) complexes [CuL2][PF6] (L = 1–5) have been fully characterized. The single crystal structures of 2[Cu(1)2][PF6]}·3Me2CO, [Cu(2)2][PF6], 2[Cu(3)2][PF6]}·Et2O and [Cu(5)2][PF6]·CH2Cl2 have been determined. The first three structures show similar distorted tetrahedral environments for the Cu+ ions with angles between the least squares planes of the bpy domains of 85.6, 86.4 and 82.9°, respectively; in contrast, the Cu+ ion in [Cu(5)2][PF6]·CH2Cl2 is in a flattened coordinate environment due to intra-cation face-to-face π-interactions. The solution absorption spectra of the complexes with ligands 1–4 are virtually identical with an MLCT band with values of λmax = 481–488 nm. In contrast, the absorption spectrum of [Cu(5)2][PF6] shows two broad bands in the visible region. Cyclic voltammetric data show that oxidation of the copper(I) centre occurs at a more positive potential in [Cu(2)2][PF6], [Cu(3)2][PF6] and [Cu(4)2][PF6] than in [Cu(1)2][PF6] or [Cu(5)2][PF6] with the latter being oxidized at the lowest potential. The complexes have been used to prepare dye-sensitized solar cells (DSCs) incorporating heteroleptic dyes of type [Cu(L)(Lanchor)]+ where L is 1–5 and Lanchor is a 6,6′-dimethyl-2,2′-bipyridine functionalized in the 4- and 4′-positions with phosphonic acid groups with (Lanchor = 7) and without (Lanchor = 6) a spacer between the metal-binding and anchoring domains. The presence of the spacer results in enhanced performances of the dyes, and the highest energy conversion efficiencies are observed for the dyes [Cu(3)(7)]+ (η = 2.43% compared to 5.96% for standard dye N719) and [Cu(5)(7)]+ (η = 2.89% compared to 5.96% for N719). Measurements taken periodically over the course of a week indicate that the cells undergo a ripening process (most clearly seen for [Cu(5)(6)]+ and [Cu(5)(7)]+) before their optimum performances are achieved. IPCE (EQE) data are presented and confirm that, although the photo-to-current conversions are promising (37–49% for λmax ≈ 480 nm), the copper(I) dyes do not realize the broad spectral response exhibited by N719.
描述了合成五种均配铜(I)配合物[CuL2][PF6]的过程,其中L是4,4′-二(4-溴苯基)-6,6′-二烷基-2,2′-联吡啶配体(化合物1-4分别具有甲基、正丁基、异丁基和己基取代基)或4,4′-二(4-溴苯基)-6,6′-二苯基-2,2′-联吡啶(5)。新配体2-5和铜(I)配合物[CuL2][PF6](L=1-5)已得到充分表征。已测定2[Cu(1)2][PF6]}·3Me2CO,[Cu(2)2][PF6],2[Cu(3)2][PF6]}·Et2O和[Cu(5)2][PF6]·CH2Cl2的单晶结构。前三个结构显示Cu+离子处于类似扭曲的四面体环境中,bpy域的最小二乘平面的夹角分别为85.6、86.4和82.9°;相比之下,[Cu(5)2][PF6]·CH2Cl2中的Cu+离子由于阳离子内部的面对面的π相互作用处于扁平的配位环境中。配合物与配体1-4的溶液吸收光谱几乎相同,具有λmax=481-488 nm的MLCT带。相比之下,[Cu(5)2][PF6]的吸收光谱在可见区显示出两个宽阔的带。循环伏安数据表明,铜(I)中心的氧化在[Cu(2)2][PF6]、[Cu(3)2][PF6]和[Cu(4)2][PF6]中比在[Cu(1)2][PF6]或[Cu(5)2][PF6]中发生在更高的电位,后者被氧化在最低电位。这些配合物已被用于制备染料敏化太阳能电池(DSCs),整合了[Cu(L)(Lanchor)]+型杂配体染料,其中L是1-5,Lanchor是6,6′-二甲基-2,2′-联吡啶,在4-和4′-位置带有膦酸基团(Lanchor=7)和没有间隔基(Lanchor=6)在金属结合和锚定域之间。间隔基的存在导致染料性能增强,最高的能量转换效率在染料[Cu(3)(7)]+(η=2.43%,而标准染料N719为5.96%)和[Cu(5)(7)]+(η=2.89%,而N719为5.96%)中观察到。一周内的定期测量表明,电池经历了一个成熟过程(最明显的是[Cu(5)(6)]+和[Cu(5)(7)]+),然后达到最佳性能。IPCE(EQE)数据显示,尽管光对电流的转换有希望(λmax≈480 nm时为37-49%),但铜(I)染料未能实现N719展示的宽光谱响应。