氰根有机磁性半导体“自旋筛”电致发光器件的物性研究

The luminous efficiency can be greatly improved by increasing the proportion of singlet excitons for the emitting from organic light-emitting devices (OLED). It is a new way to increase the distribution ratio of singlet exciton by injecting a carrier with a given spin orientation into a luminescent material. Organic magnetic semiconductor was discovered for providing the possibility for the realization of this idea. Science it has organic and magnetic properties at room temperature. With forward bias, the holes injected from the p-layer and the electrons injected from the n-layer pair up to form excitons in the OLED. An exciton can be either a triplet or a singlet. For most organic emitter, the singlet exciton decays radioactively and rapidly emitting a photon but the triplet exciton decays non-radioactively. Thus, the relative population of triplet and singlet excitons determines the internal quantum efficiency of the OLED. For unpolarized carrier injection, the probability of forming a triplet is 75 %. Therefore at least 75% of electron-hole recombination events are wasted in heat, and the maximum internal quantum efficiency is limited to meager 25 %. This situation can be changed if spin polarized holes and electrons are injected in the OLED. It would then be possible to preferentially form triplets or singlets by controlling the spin polarizations of the injected carriers. Using this method, the relative population of the singlet and hence the internal quantum efficiency can reach a theoretical maximum, leading to brighter and more energy-efficient OLED. For this to happen, it is necessary to ensure that the exciton formation and radiative recombination rates are much larger than the spin relaxation rate. Thus for this purpose, long spin relaxation times are desirable and are indeed achievable in optically active organic compound like Cyanogen, Poly-BIPO, V[TCNE]x. In this project, we will investigate the intrinsic spin polarization using a novel spin filter structure. We believed that spin polarized holes and electrons were injected in an OLED structure which led to increase in the electroluminescence efficiency and device lifetime compared to the case when both type of carriers are unpolarized. This project will focus on field, micro-structure, interface, material matching, device structure, manufacturing process and effect of temperature on the spin injection and transport by using the magnetic field probe, XAFS, VSM, XPS, TEM and other experimental characterization methods, combined with the one-dimensional tight binding SSH+Heisenberg model and Green function method. The research of this project will try to achieve the quantitative results and decisive conclusions, thoroughly analyzing the microscopic mechanisms of spin injection and transport, and promoting the progress in the aspects of theoretical explanation and device application of spin-OLED research.

在有机电致发光器件（OLED）发光过程中，如果能提高单线态激子的比例，就会大大提高器件的效率。通过“自旋筛”向发光材料注入具有给定自旋取向的载流子是提高单线态激子分布比例的一种新思路。而集有机材料和磁性材料特性于一身的室温有机磁性半导体的发现，为这种思路的实现提供了可能。本项目拟利用氰根系列和Poly-BIPO等室温有机磁性半导体分别作为“自旋筛”，构建一种对电子和空穴同步过滤的独特器件结构。着眼于载流子传输过程，试图对其自旋态进行操控，提高发光层单线态激子的比例，研制成功新型、高效“自旋筛”OLED。运用磁场探针、XAFS、VSM等实验表征手段，结合一维紧束缚SSH模型和格林函数方法，探讨外场、微结构、界面、材料匹配、器件结构、制备方法等因素对自旋注入和输运的影响。力图获得定量的结果和确定性的结论，深入解析自旋注入和输运的微观物理机制，促进自旋相关的发光器件机理解释与应用两方面的发展。

本项目利用新型有机半导体R-NDCQNU和S-NDCQNU作为“自旋筛”，构建了一种对电子和空穴同步过滤的独特器件结构。着眼于载流子传输过程，对其自旋态进行操控，提高发光层了单线态激子的比例，研制成功新型、高效“自旋筛”OLED。这些被极化的电子和空穴在器件发光材料内部相遇，形成单线态激子的比例接近于50%，相应器件的效率高达10.20 cd/A，是普通参比器件的1.58倍。运用磁场探针等实验表征手段，结合一维紧束缚SSH模型和格林函数方法，探讨了外场、微结构、界面、材料匹配、器件结构、制备方法等因素对自旋注入和输运的影响。分别从实验和理论两个方面展开研究，圆满完成了本项目任务书制订的研究计划，取得了一系列有特色的成果。在国际和国内学术刊物发表高质量论文 29 篇；申请国家发明专利 3项，其中2项已经被授权，一项正在公示；培养研究生 16 人，培养本科生 33 人；荣获重庆市自然科学奖（三等）1项（本项目主持人排名第一）；本项目主持人被重庆市委组织部等6部委评为重庆市创新科技领军人才；本项目课题组成员陈丽佳博士晋升为教授。