双共轭链及取向调控对环状硫脲染料光物理和光伏性能影响研究

Dye-sensitized solar cells (DSSCs) are one of the most attractive research topics in the new and clean energy area. Among others, the research on how to broaden the absorption bands and increase the absorption intensity of sensitizers have an important impact on the improved performances of the DSSCs, and thereby being a bottleneck for further development of DSSCs. On basis of the fact that an increase of the conjugated system can broaden the absorption spectrum and the question how to affect the photovoltaic properties by double conjugation linkages and its mechanism, a series of new dye molecules are designed, in which the cyclic thiourea benzopiperazine as a donor is connected at 4,5 position with double conjugation linkages and tuned their orientation in this project. It will focus on the relationship of the impact of bis-axes angles on their photophysical, electrochemical, orbital energy level and dye-loading properties. A theoretical mode of the relationship between stereo configuration and properties will be established. The contents involve a combination of the cyclic thiourea functionalized donor, invented by our group, with an increase of conjugated system. Theoretical molecular modulation, synthetic methodology, measurements of UV-vis absorption, Cyclic Voltammetry and Impedance, and Thermal Analysis for dye loading will be used to obtain the corresponding physical and chemical parameters. Finally, the correlation of the physical and chemical properties with the stereo structures will be carried out, which will be significant to design and synthesize the valuable dye sensitizers, and prompt the development of the DSSCs.

染料敏化太阳能电池（DSSCs）是清洁新能源领域的主要研究方向之一，而光敏染料的光吸收范围和强度是决定电池效率的关键因素，也是制约DSSCs发展的主要瓶颈。基于增加共轭体系可以拓宽分子吸光谱带的事实和共轭桥链增加对光伏性能影响机制尚不清楚的问题，本项目在已有环状硫脲三苯胺为供体的基础上，设计增加共轭链并调控其取向，探索两个共轭链夹角对其光物理性能、电化学性能和光伏性能的影响规律，建立该类染料分子立体结构与性能之间的理论关系。项目将已发明的环状硫脲供体与多种共轭体系相结合，从分子计算模拟、合成方法探索到测试紫外可见吸收光谱和电化学能级等物理化学参数研究，最终关联其结构与光物理和光伏性能，为高性能光敏染料分子的设计与合成提供理论基础。本研究对合成高效有机光敏染料、促进染料敏化太阳能电池领域的进步有重要意义。

本项目主要研究了：1. 环状硫脲供体染料中桥链二面角对光物理及光伏性能的影响。①桥链中共轭单元（苯环、噻吩、呋喃）对光物理及光伏性能的影响；②在桥链中增加辅助受体（D-A′-π-A，D-π-A′-A）对光物理及光伏性能的影响；③桥链中增加共轭供电子基因对光物理及光伏性能的影响。上述研究结果表明，二面角大有助于抑制团聚，但角度过大，电子传输性能下降。桥链中引入苯基能提高开路电压，但是降低桥链的电子传输效率，而五元杂环的效果正好与苯基相反，噻吩基是桥链中比较好的共轭单元。增加辅助受体能显著提高捕光强度，特别是D-π-A′-A型分子中，由于分子偶极矩的增加，光伏性能明显增加。供电子烷基苯引入到桥链中，增加了共轭效应，拓展了捕光能力，对光伏性能有提升作用。2.双（D-π-A）是以乙烯为中心，一端双氢被供体取代（环状硫脲三苯胺、三苯胺、甲氧基三苯胺），另一端双氢被π-A桥链取代，合成了剪刀状双（D-π-A）染料。该类染料都具有很强的捕光能力和高的光电转化效率。从供体来说，环状硫脲三苯胺＞三苯胺＞甲氧基三苯胺。桥链的夹角越小，染料的负载量越大，但是光伏性能变化不明显，其中甲氧基三苯胺性能较差。环状硫脲双（D-π-A）染料的光电转化效率最高达到9.33%，经过20多批次的DSSC制备及测试，其光电转化效率集中在8.4%-9.3%之间。该双（D-π-A）染料的突出特点是稳定性高，在3000小时的稳定性考查中，能够保持效率在初始值的98%以上，详细机理仍在研究中。上述研究从染料分子中桥链夹角、共轭单元、增加辅助供体和受体等对光物理及光伏性能影响方面进行了全面的探索，能够对高性能染料的分子设计提供有益的借鉴。双（D-π-A）染料的捕光性能，光伏性能和器件稳定性明显优于D-π-A染料。双桥链既有良好的捕光作用，也是提高和稳定染料负载的主要因素。对今后高效高稳定敏化染料分子的设计具有重要的指导意义。