Organic dye-sensitized ionic liquid based solar cells:: Remarkable enhancement in performance through molecular design of indoline sensitizers
Organic dye-sensitized ionic liquid based solar cells:: Remarkable enhancement in performance through molecular design of indoline sensitizers
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DOI：
10.1002/anie.200705225
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Graetzel, Michael
中科院分区：
文献类型：
--
作者：
Kuang, Daibin;Uchida, Satoshi;Graetzel, Michael
染料敏化太阳能电池（DSCs）相对于传统的晶体硅太阳能电池具有低成本、易制备、灵活性和透明性等潜在优势，在科学研究和实际应用中引起了极大的关注。[1，2]在过去的十年中，在DSC器件的性能和稳定性方面取得了重大进展。[3-6]敏化剂是染料敏化太阳能电池中的关键元素，对器件的能量转换效率和稳定性有重要影响。尽管迄今为止最有效的敏化剂是钌络合物，但有机染料由于其易于合成、高摩尔消光系数、从可见光到近红外（NIR）区域的可调谐吸收光谱响应以及环境友好和廉价的生产技术而吸引了大量的研究工作。[7-10]最近，据报道，与挥发性溶剂（例如乙腈）电解质组合使用的有机染料敏化太阳能电池的功率转换效率为9%。[7b]由于在较高温度下的封装和稳定性问题，非挥发性或离子液体电解质优于挥发性类似物。离子液体（IL）尤其是非常有吸引力的，因为它们在光伏操作条件下可忽略的蒸气压以及它们的高导电性和热稳定性。[4，11-15]具有钌络合物作为敏化剂的IL基DSC已经显示出令人印象深刻的光伏性能和稳定性。[4，11]然而，它们的转化效率仍然落后于含有有机溶剂的DSC。性能较低的主要原因是离子液体的高粘度，这对全光照下的光电流产生了传质限制。有机敏化剂提供了非常有吸引力的前景，以克服这一缺点，因为它们在可见光的消光系数远高于那些钌配合物使用至今。这使得光捕获可以用更薄的TiO 2膜来完成，从而缓解了质量传输问题。在这里，我们报告的实现7.2%的太阳能（空气质量（AM）1.5，100毫瓦厘米↑ [2]照射）的电力转换效率，使用分子定制的吲哚啉敏化剂。据我们所知，这是第一次使用离子液体电解质获得如此高的效率。电化学阻抗和光电压瞬态研究揭示了吲哚染料的化学结构对器件光伏响应的关键影响。本研究中研究的三种吲哚啉基有机染料的分子结构见图1。D149敏化剂是通过将第二个若丹宁单元连接到D102 [7a]结构上，从而扩展其π共轭而获得的。用辛基链取代D149末端若丹宁单元上的乙基，得到系列中的第三种敏化剂，编码为D205。这三种敏化剂的合成方法如前所述。[7a]D149和D205中增加的共轭导致可见光谱相对于D102的红移。因此，D149在叔丁醇中和D205在THF中的最大吸收分别位于λ= 526 nm（ε= 68 700 mJ/cm ↑ [-1]）和532 nm（ε= 53 000 mJ/cm ↑ [-1]），而D102在THF中的最大吸收位于λ= 494 nm（61 000 mJ/cm ↑ [-1]）。[7a]二氢吲哚染料在介观TiO 2薄膜表面上的吸附拓宽了它们的吸收光谱，并且最大峰值向红色的移位最有可能是由于J聚集体的形成。[7c]图2a显示了基于IL的DSC的电流-电压特性.
Dye-sensitized solar cells (DSCs) have attracted large attention in scientific research and for practical applications owing to the potential advantages of low cost, easy production, flexibility, and transparency relative to conventional crystalline silicon solar cells.[1, 2] Over the past decade, significant progress was made in terms of the performance and stability of DSC devices.[3–6] The sensitizer is a crucial element in DSCs, exerting significant influence on the power conversion efficiency as well as the stability of the devices. Although the most efficient sensitizers to date are ruthenium complexes, organic dyes have been attracting intensive research efforts because of their ease of synthesis, high molar extinction coefficient, tunable absorption spectral response from the visible to the near infrared (NIR) region, as well as environmentally friendly and inexpensive production techniques.[7–10] Recently, 9% power conversion efficiency was reported for an organic-dye-sensitized solar cell used in combination with a volatile solvent (eg, acetonitrile) electrolyte.[7b] Owing to encapsulation and stability issues at higher temperatures, nonvolatile or ionic-liquid electrolytes are preferred over volatile analogues. Ionic liquids (ILs) in particular are very attractive because of their negligible vapor pressure under photovoltaic operating conditions as well as their high conductivity and thermal stability.[4, 11–15] IL-based DSCs with ruthenium complexes as sensitizers have already shown impressive photovoltaic performance and stability.[4, 11] However, their conversion efficiency still lags behind those of organic-solvent-containing DSCs. The main reason for the lower performance is the high viscosity of ILs, which produces mass-transfer limitations on the photocurrent under full sunlight. Organic sensitizers offer very attractive prospects to overcome this drawback, as their extinction coefficients in the visible are much higher than those of the ruthenium complexes employed so far. This allows light harvesting to be accomplished with thinner TiO2 films, alleviating the masstransport problem. Herein we report on the achievement of 7.2% solar (air mass (AM) 1.5, 100 mWcmĄ2 irradiation) to electric power conversion efficiency using a molecularly tailored indoline sensitizer. To our knowledge this is the first time such high efficiency has been obtained for organicdye-based DSCs employing an ionic-liquid electrolyte. Electrochemical impedance and photovoltage transient studies reveal the pivotal influence exerted by the chemical structure of the indolene dye on the photovoltaic response of the device.The molecular structures of the three indoline-based organic dyes examined in this study are presented in Figure 1. The D149 sensitizer was obtained by attaching a second rhodanine unit to the D102 [7a] structure, thus extending its π conjugation. Replacing the ethyl group on the terminal rhodanine unit of D149 by an octyl chain yields the third sensitizer in the series, coded D205. The three sensitizers were synthesized as reported earlier.[7a] The increased conjugation in D149 and D205 results in a red shift of the visible spectrum with respect to D102. Thus, the absorption maxima for D149 in the tert-butyl alcohol and D205 in THF are at λ= 526 nm (ε= 68 700mĄ1 cmĄ1) and 532 nm (ε= 53 000mĄ1 cmĄ1), respectively, whereas that of D102 in THF is located at λ= 494 nm (61 000mĄ1 cmĄ1).[7a] Adsorption of the indoline dyes on the surface of the mesoscopic TiO2 films broadens their absorption spectrum, and a shift of the peak maxima to the red results most likely from the formation of J aggregates.[7c] Figure 2 a shows the current–voltage characteristics of the IL-based DSCs …