D-A型二元嵌段共聚物的合成及其在单一组分全聚合物太阳能电池中的应用

In bulk heterojunction photovoltaic cell, phase separation beteen donor and acceptor is beneficial to form interpenetrating networks and realize high conversion efficiency.Compared to polymer/fullerene, all polymer BHJ PSCs have the advantage of wider absorption, fine-tuning of structure and energy levels of the acceptor materials, higher open-circuit voltage,superior polymer/polymer blends and flexibility in large area and large scale solution processed film coating. Fully conjugated donor-acceptor diblock polymers have better phase separation than its donor/acceptor polymer blends. However,there's very limited examples of these materials,especially D-A diblock conjugated polymer as single component active layer has never been reported to date. Thus, in this project, diblock conjugated polymers by using P3HT as donor unit and various acceptor units are firstly designed. The phase separation behavior between donor and accetor and their application as photo-active layer in all polymer solar cells will also be investigated by camparison with donor/acceptor polymer blend systems. High charge mobility, suitable LUMO level and wide absorption accetor polymers will be further designed and sythesized through carefully tuning of chemical structure to synthesize and construct the diblock D-A conjugated polymers.It is expected to realize high open-circuit voltage and high photo-electron conversion effieciency all polymer solar cell by using the newly designed D-A diblock conjugated polymers as single component active layer. This project is also expected to provide significantly important theory and technical guidance for highly efficient all polymer solar cells and design of superior polymer opto-electronic materials.

在本体异质结光伏电池中，给受体材料间纳米级相分离是形成隧穿网络结构和实现高电池效率的前提。相比聚合物/富勒烯，全聚合物体异质结电池具有材料吸收范围宽、受体结构和能级可灵活调控、开路电压高、聚合物间相容性好，适于大面积、大规模制备等优点。全共轭给-受体型二元嵌段聚合物可获得比给-受体聚合物物理共混膜更好的相分离，但对此类材料的研究极少，尤其将其作为单一活性层的电池未见报导。基于此，本项目拟设计合成以P3HT为给体、不同受体结构的全共轭D-A型二元嵌段共聚物。通过与给-受体物理共混体系对比，系统研究化学键合的嵌段共聚物在相分离和全聚合物太阳能电池中的优越性。进一步优化分子结构，设计具有高电子迁移率、合适LUMO能级、宽吸收光谱的受体及其二元嵌段共聚物，进而制备高开路电压、高效率的单一组分聚合物光伏电池。这对提高全聚合物光伏电池效率和设计性能优异的光电材料具有重要的理论与实践意义。

具有实用意义的全共轭D-A型嵌段共聚物的可控合成是目前国际化学合成的挑战性难题，至今尚无人突破。现有的合成方法仅可实现给体链段P3HT 的可控聚合，而受体链段通常采用逐步缩聚反应，通常合成的嵌段共聚物包含多组分，例如产物二元嵌段共聚物，游离的聚合物给体链和受体链，以及极少量三元嵌段共聚物。合成方法的挑战，大大影响了该领域的发展。本项目在现有技术的基础上，进一步通过制备色谱进行聚合物分离提纯，可获得给、受体聚合物链段长度可调、PDI窄（1.1~1.3）的单分散型全共轭D-A型嵌段共聚物。尤其通过选择具有互溶以及正交溶解性的给、受体聚合物，可有效地调控嵌段共聚物相分离程度。本项目具体开展工作如下。.1) 将具有平衡载流子传输性能的单分散型D-A 型嵌段共聚物P3HT-b-PNBIT2(μh: 2.36×10-4, μe: 1.15×10-5 cm2/V s)作为单一组分活性层，获得最简单结构聚合物太阳能电池效率为1% (New J. Chem., 2016, 40,1825-1833.)；.2) 通过维持D-型P3HT 链长度基本不变，依次调节A-型受体聚合物链段长度，可实现嵌段共聚物P3HT-b-PNDIT 的能级梯度调控(Chin. J. Chem., 2015, 33, 865-872)；.3) 保持受体聚合物PNDIT2 链长度~40-50 kg/mol， 增加P3HT 链由5 、9 至26 kg/mol，发现嵌段共聚物器件效率逐步提升；.4) 在P3HT-b-PNDIT2 及P3HT-b-PNDITBT体系中，改变受体单元结构可有效调控嵌段共聚物的相分离，发现化学键合的D-A 型嵌段共聚物比物理共混体系具有更佳的成膜质量、更好的相分离以及更高的光电转换效率；.5) 选择在氯仿中具有正交溶解性的P3HT 为给体，PCDTBT 为受体，通过制备色谱进一步分离提纯，可最大限度提升嵌段共聚物纯度。将D-A型嵌段共聚物P3HT-b-PCDTBT 以5 wt%的比例作为P3HT/PCBM 的增溶剂，可实现电池光电转换效率的提升。我们的工作为全共全共轭D-A 型嵌段共聚物的发展前景提供了良好的基础(Chin. J. Polym. Sci, 2017, 35, 207-218)。.本项目为全共轭D-A型嵌段共聚物的多功能应用前景提供良好基础。