具有光诱导分子内电子转移的柱状相盘状液晶光伏材料的合成及性质研究

In order to improve the power conversion efficiencies of the organic solar cells, in this project designing and synthesizing organic photovoltaic materials made from discotic columnar liquid crystals having photoinduced intramolecular electron transfer behavior are presented, in the way that the problems of exciton loss and carrier loss would be addressed. The molecules designed have donor, acceptor and bridge (/and chromophore) components. When excited there are photoinduced intramolecular electron transfer in the molecules, resulting in charge-separated states, that is the donor becomes positively charged and the acceptor becomes negatively charged. While the charges recombination can be slowed down by applying 'electron spin control' and 'inverted-region effect', etc. The discotic columnar liquid crystal molecules usually form columnar phases, which generally have high charge carrier mobility and used as 1D nanowires. When the materials face-on align on the surfaces of the electrodes, electrons and holes can pass through the nanowires which are perpendicular to the electrode surfaces, respectively, reaching the cathode and the anode. Thus the carrier loss decreases. Through choosing the candidates of donors, acceptors and bridges (/and chromophores), and using the computer simulation at the same time, the discotic liquid crystal dyads and triads which have specific absorption in the solar spectrum, having columnar phase and photoinduced intramolecular electron transfer, would be synthesized. In addition, the properties, such as the temperature ranges of the mesophase, the types of the liquid crystal phases, how they aligning on the substrates, the rates of the photoinduced intramolecular electron transfer, and life times of the charge-separated states, and how they affecting the power conversion efficiencies of the organic photovoltaic devices, will be investigated fully and thoroughly.

为了提高有机太阳能电池的效率，本项目以减少激子损失和载流子损失为途径，设计并合成具有光诱导分子内电子转移的柱状相盘状液晶光伏材料。该类材料分子内含有电子给体单元、受体单元和桥体。吸收光能后，激发态分子内发生快速电子转移，产生电子和空穴，而其复合可以通过电子自旋控制、反转区效应等方法得到抑制；由于柱状相盘状液晶分子易自组装，生成柱状相，其载流子迁移率较高，可作为一维纳米导线使用。当盘状液晶在电极表面垂面取向时，空穴和电子分别通过垂直于电极表面的纳米线高效传输到正、负极，从而减少载流子损失。具体工作为：选择具有不同结构的给体、受体、和桥体或生色团，并借助计算机分子模拟，设计新结构，探索并优化合成方法，合成在太阳光波段内具有选择性光吸收的柱状相盘状液晶二元和三元化合物；进而研究材料的液晶性质、在不同衬底上的取向性、光诱导分子内电子转移的速率常数、电荷分离态寿命、以及对电池效率的影响。

有机太阳能电池具有轻便、柔性和可溶液加工的特点，三十多年来一直是科学研究的热点之一。本课题利用盘状液晶具有自修复缺陷和在柱状相时具有较高载流子迁移率的特点，以提高激子拆分效率和提高载流子传输速率为目的，设计一系列含有电子给体（D）单元和受体（A）单元的二元和三元化合物。目前已经合成以烷氧基苯并菲和烷氧基卟啉为D单元，以二烷基苝二酰亚胺、苝四甲酸四烷基酯、苝单亚胺二甲酸二烷基酯和烷氧基卟啉为A单元，以柔性烷氧基和刚性乙炔基苯基为桥的二元和三元化合物。通过核磁共振、元素分析和红外光谱等手段对目标产物进行结构表征。通过紫外可见有收光谱、荧光光谱、电化学工作站、偏光显微镜、示差扫描热分析、X-射线衍射、真空镀膜仪等手段和仪器研究材料的液晶性质、能级结构（电子的最高占有分子轨道, 最低未占有分子轨道和光学带隙）、光电导及光伏性质。实验结果表明，当给体单元和受体单元均具有柱状液晶相，柔性链连接的D-A型二元化合物桥体长度在某一临界值以下时，二元化合物没有液晶性质；在临界值以上时，具有液晶性质，且为液晶柱状相；降温时含有卟啉和苯并菲单元的二元化物液晶材料易在玻璃表面形成垂面取向；刚性桥连接的D-A型二元化合物，在桥体较短时有利于形成液晶相，而桥体较长时，液晶相反而消失；三元化合物的液晶性比较复杂。在可见光照射时，具有液晶性的二元化合物能够发生有效的分子内电子转移，生成具有电荷分离态的分子。苯并菲-乙炔基苯基桥-苝单亚胺二酯二元化合物具有分子内光诱导电子转移效率接收1和六方柱状液晶相的性质。在光照时光电流响应曲线证实该分子生成电荷分离态。此外，柔性链桥接的苯并菲-苝二酰亚胺-苯并菲-三元化合物可以作为非富勒烯受体，与P3HT共混制备的光伏器件具有明显的光伏响应性。因此，含有D、A单元且具有柱状液晶相的二元和三元化合物具有作为新型有机光伏材料的前景。