单晶衍射技术在有机太阳能电池受体材料中的应用

The application of single crystal diffraction technique in organic solar cells

有机太阳能电池器件的光电转化效率已超过18%.为了进一步推动其发展,有必要从原子层面上了解材料的堆积信息,来帮助设计和开发性能优异的受体分子.通过单晶X射线技术可观察到的分子在固态下的堆积排列方式和分子间的相互作用力,通常被用来指导设计具有预期物理化学性质的材料.本文主要讨论单晶X射线衍射技术在非富勒烯有机太阳能电池受体中的应用进展,着重强调受体材料结构设计、堆积排列和器件性能之间的关系.此外,我们发现了受体分子"三维网络堆积"的现象,对比了其在A-D-A体系和A-DAD-A体系中的不同,研究了其在氯取代、氟取代、溴取代和三氟甲基取代体系中的特性.对三维网络传输的理解可为高性能材料的设计提供指导,通过单晶分析理解和调整材料的聚集状态和分子间相互作用对开发新型受体具有重要意义.

As one of the most promising technologies for production of clean and renewable energy,solar cells which convert light to electricity have attracted a great deal of attention.Here,the power conversion efficiency of organic solar cells has exceeded 18%.In order to further promote the device performance,it is necessary to understand the packing information from the atomic level to help design next generation materials.Single crystal X-ray technology can be used to observe the packing arrangement of molecules in the solid state and understand the intermolecular interactions,which is usually applied to guide the designing of materials with expected physical and chemical properties.This review mainly discusses the application of single crystal X-ray diffraction technique in the non-fullerene acceptors of organic solar cells,with emphasis on the relationship between the structure design,packing arrangement and device performance of materials.For example,we found more ordered J-aggregates in chlorinated acceptor compared its fluorinated and hydrogenated analogues due to the empty 3 d orbitals chlorine atom can accommodate lone pairs of sulfur atom to enter into extra noncovalent interactions.Then,it is proved that the isomerization has a great effect on molecular packing arrangements and photovoltaic performance:In general,the substitution of halogen at the γ-position is better than at the δ-or β-position in IC groups,the substitution of halogen at the γ-position of an IC group might be an important way to construct the 3 D network packing structures.Next,the electron coupling values can be effectively improved to some extent by increasing the halogenated numbers.In addition,we found the phenomenon of "3 D network packing" of acceptors,where it can be considered as the electron transported along x,y and z directions,where one more group of molecules in the x-axis direction,aligned to the y-axis group of molecules by well-ordered π…π stacking end group tunnels to form a closed shape of rectangle or ellipse,endowing it a 2 D transmission property in the x-y plane,cooperated with the π…π hopping along z-axis,the 3 D transport property in three directions can be realized,which is similar to the isotropic charge transfer of fullerene acceptors.The packing models from 1 D to 2 D and to a 3 D π…π stacking are compared in this review,it was found the increased mobilities from 1.43×10-5 to 2.7×10-4 and to 8.3×10-4 cm2 V-1 S-1 were realized in the system,this suggests a better coplanar molecular configuration would encourage a closer and more ordered packing arrangement,and a more promising 3 D network structure by π…π stacking from x,y,and z directions can be realized by combining Br…S and Br…π intermolecular interactions.Finally,the intermolecular interactions and aggregation states in A-DAD-A-type acceptors are significantly different from that in A-D-A-type acceptors,the coordinated H/J-aggregates leading to more electron transport channels,it might be an important reason for the high efficiency of A-DAD-A-type acceptors,and we also studied their characteristics in chlorine-,fluorine-,bromine-,and trifluoromethyl substituted systems.In conclusion,understanding and adjusting the aggregation state and intermolecular interaction of materials through single crystal analysis is of great significance for the development of new acceptors.