光-电双激发模式下有机半导体中的激子行为及相关磁效应

Magnetic field effects (MFEs) in organic semiconductor are among the hot topics in modern organic electronics. Many studies have demonstrated that the current and electroluminescence of the organic devices show pronounced magnetic field responses when the devices are submitted to external magnetic field. However, many critical issues in the MFEs are still not clear, in particular, the role of the excitons on MFEs. In this project we intend to resolve this issue by applying a novel experimental method, called Synchronous Optical and Electrical Excitation (SOEE) mode, in which the number and distribution of exctions and current passing through the devices can be controlled separatedly and effectively by varying the intensity and wavelength of excitation light and by changing the amplitude and direction of drive voltage, respectively. Then, we plan to study the physical origin of three interesting findings obtained in the feasibility studies under SOEE mode. The three findings are (i) magnetoconductance (MC) with 'W' shape at low field (B<200 mT) scale in single layer devices, (ii) different field dependence of MC at high field (B>50 mT) scale in double layer deveices, and (iii) sign invension of MC in doped devices, respectively. The exciton behavior and the role of exciton on the above MFEs under SOEE mode will be discussed specifically. This project is expected to establish the physical model for these intriguing MFEs and find out the key factors that determine the MFEs, laying the foundation for the development of novel multifunctional organic devices with integrated magnetic, optical, and electronic properties. Therefore, we believe that this project is of significant research value and broad application prospect.

有机半导体中的磁效应是当前有机电子学研究领域中的热点问题之一。尽管大量研究表明有机半导体器件中的电流和发光强度在外加磁场作用下会表现出明显的磁响应，但是对其所涉及的微观机制目前存在较大争议，特别是激子在有机磁效应中所扮演的具体角色还不确定。针对这一科学问题，本项目采用光-电双激发模式，实现对激子和载流子的有效控制，重点研究光-电双激发模式下有机磁效应出现以下三种新现象的物理起源：即单层器件磁电导效应在低场附近出现"W"型新峰位、双层器件磁电导的高场部分在正负偏压下出现相反变化趋势以及掺杂器件中正负磁电导的转变，具体讨论有机半导体中的激子行为在上述磁效应产生过程中所起的作用。本项目将构建有机磁效应与激子演变过程之间的关联，建立和完善有机磁效应的微观机制，并确定出影响有机磁效应的关键因素，为开发集磁-光-电各项性能于一体的新型有机功能器件奠定基础，因此具有明显的研究价值和较好的应用前景。

有机磁效应是当前有机电子学领域中的热点问题之一。这是因为有机磁效应不仅在磁存储和磁传感器方面具有巨大的应用前景，同时有机磁效应也可以作为一种探测有机半导体内部电荷输运、激发态演变和自旋输运等微观过程的强有力工具。尽管大量研究表明有机半导体器件中的电流和发光强度在外加磁场作用下会表现出明显的磁响应，但是对其所涉及的微观机制目前存在较大争议，特别是激子（或激发态）在有机磁效应中所扮演的具体角色还不确定。在本项目中，我们采用光-电双激发模式，实现对激子和载流子的有效控制，重点研究了电子-空穴对，激子、双极化子对以及激基复合物等激发态对有机磁效应的产生机制和作用条件，并探索了有机磁效应研究结果在实验教学中的应用。本项目所取得的研究成果如下：（1）确定了电子-空穴对机制在平衡注入条件下会导致具有洛伦兹线型的磁效应产生；而在非平衡注入条件下，三重态激子与电荷的相互作用占主导，并产生具有非洛伦兹线型的磁效应，发现了‘三重态激子与电子’和‘三重态激子与空穴’的作用强度并不一致；（2）证实了有机半导体中的缺陷态可以促进双极化子对的形成，并导致负磁电导效应的产生；（3）发现了磁电导的正负转变过程可以通过调节单重态激子的裂变、辐射和分离等过程来实现；（4）掌握了决定激基复合物发光磁效应的主要因素，并获得了目前为止在有机半导体器件中发现的最大磁效应。本项目在执行过程中，共计已发表SCI论文9篇，教学研究论文1篇，申请国家发明专利1项，达到了预期的研究目标。