A Series of Squaraine Dyes: Effects of Side Chain and the Number of Hydroxyl Groups on Material Properties and Photovoltaic Performance
A Series of Squaraine Dyes: Effects of Side Chain and the Number of Hydroxyl Groups on Material Properties and Photovoltaic Performance
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DOI：
10.1021/cm4034929
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发表时间：
2014-02-11
影响因子：
8.6
通讯作者：
Kido, Junji
中科院分区：
文献类型：
--
作者：
Chen, Guo;Sasabe, Hisahiro;Kido, Junji
方酸菁染料被认为是有机光电器件领域中一类重要的光活性材料。在这项工作中，我们特意调整了一系列方酸菁（SQ）染料（即SQ1 - 4）的侧链和羟基（OH）基团的数量，以研究结构变化对材料性能的影响以及这些染料作为体异质结（BHJ）光伏电池中的给体材料的性能。使用各种工具对这些方酸菁的材料结构和性能进行了系统表征。基于这些方酸菁化合物并与[6,6]-苯基 - C71 - 丁酸甲酯（PC71BM）作为受体的溶液处理的体异质结光伏电池在100 mW/cm²的AM 1.5G太阳光照下实现了大于4.0%的有效功率转换效率。我们的观察结果表明，羟基使给体的最高占据分子轨道（HOMO）能级降低，从而提高了开路电压，而线性链改善了体异质结薄膜中的电荷传输性能。侧链和羟基的数量在决定这些方酸菁在固态薄膜中的聚集行为方面都起着重要作用：含有四个羟基和支化侧链的SQ1由于其侧链的空间位阻而呈现J - 聚集；含有四个羟基和线性侧链的SQ2呈现H - 聚集和J - 聚集；含有两个羟基和线性侧链的SQ3呈现优先的H - 聚集；含有线性侧链但无羟基的SQ4呈现J - 聚集，这很可能是由于其强烈的分子间耦合和分子间氢键相互作用形成头 - 尾堆积模式，即J - 聚集。有趣的是，体异质结电池中J - 聚集物的吸收有助于电池在长波长下的光响应，从而导致更高的光电流。我们的结果表明了方酸菁染料的分子结构与其决定光伏性能的物理性质之间的明确关系。
Squaraine dyes are considered an important group of photoactive materials in the field of organic photovoltaic devices. In this work, we purposely tuned the side chains and number of hydroxyl (OH) groups in a series of squaraine (SQ) dyes, i.e., SQ1-4, to investigate the effect of structural variations on the material properties as well as the performance of these dyes as donor materials in bulk heterojunction (BHJ) photovoltaic cells. The material structure and properties of these SQs were systematically characterized using various tools. Solution-processed BHJ photovoltaic cells based on these SQ compounds combined with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor gave efficient power conversion efficiencies greater than 4.0% under AM 1.5G solar illumination at 100 mW/cm(2). Our observations show that the OH groups deepened the highest occupied molecular orbital (HOMO) of the donor and thus enhanced the open-circuit voltage, whereas the linear chain improved the charge transport properties in the BHJ films. Both the side chain and the number of OH groups play important roles in determining the aggregation behavior of these SQs in solid-state films: SQ1, which contains four OH groups and branched side chains, exhibits J-aggregation,because of the steric hindrance of its side chains; SQ2, which contains four OH groups and linear side chains, exhibits both H-aggregation and J-aggregation; SQ3, which contains two OH groups and linear side chains, exhibits preferential H-aggregation; SQ4, which contains linear side chains without OH groups, exhibits J-aggregation, this is most likely because of its strong intermolecular coupling and intermolecular hydrogen-bonding interactions to form a head-to-tail packing mode, i.e., J-aggregation. Interestingly, the absorption of J-aggregates in BHJ cells contributes to the cells' photoresponse at long wavelengths, and thus results in higher photocurrent. Our results demonstrate a clear relationship between the molecular structures of SQ dyes and their physical properties that govern their photovoltaic Performance.