激子分裂、载流子散射和激子-电荷湮灭在有机磁效应中的作用

Large magnetic field effects (MFEs) on current and electroluminescence (i.e. MC and MEL), which are observed under small field and at room temperature in organic semiconductor devices without any magnetic active layer, have recently attracted broad interest. Despite significant advances in organic MFEs have been made, however, the mechanisms underlying the plentiful phenomena related with magnetic field responses still need to be deeply elucidated. For this project we have tried, ahead of time, four device structures to investigate the roles of singlet exciton fission into triplet exciton(STT), carriers's sccattering, and triplet exciton-charge annihilation (TQA) in organic MFEs. The physical principles related to organic MFEs could be deeply understanded by studying the temperature effects, bias dependence, and transient properties for MC and MEL through controlling the device-structure parameters such as the energy band structure, physical mixture, and carriers's density. The feasibility studies of this project show some interesting findings, that is, 'W'-lineshape or fine structure of MC were found in the singlet fission system at high and low magnetic field, respectively; hyperfine interaction which plays important roles in MEL at low field scale is not mirrored in MC of the scattering system; new lineshape of MC with smaller magnitude is found in TQA system under high field scale. This project is thought to be a significant research since it is expected to uncover deeply the mechanism of the organic MFEs based on these novel findings in three featured systems.

最近，在不包含任何磁性功能层的有机半导体器件中，发现其电流与发光在室温和小磁场下具有较强的磁效应(MC和MEL)，这引起了一个研究热潮。尽管已取得较大进展，但其不断呈现的实验新现象和多种微观机制并存的现状亟待深入研究。针对这一科学问题，本项目预研了四种器件，重点研究单重态激子分裂成三重态激子(STT)、载流子散射和三重态激子-电荷湮灭(TQA)等微观过程对有机磁效应的影响。通过控制有机功能薄膜的能带结构、共混程度以及载流子浓度等结构参数，并利用温度效应、偏压关系和瞬态特性等性质，深入理解三种微观过程的物理规律，诠释预研实验得到的新结果：即在STT体系中MC可以呈现'W'型的高场特性或振荡变化的低场特性；在散射体系中MEL有明显的超精细作用但在MC中则无相应体现；在强TQA体系中MC的高场部分出现非单调变化的新线型。该项目以实验新现象从更深层次揭示有机磁效应的物理机制，具有明显的科学价值。

有机磁场效应（Organic Magnetic Field Effects, OMFEs）不仅为研究有机光电器件内部的微观机制提供了一种非接触的、实时监测的手段，而且也拓宽了有机光电器件.的应用范围，使其在磁存储、手写输入、新型磁性传感器等方面具有巨大的应用前景。因此，对OMFEs的有效调控，无论是在基础研究还是在器件应用方面都具有非常重要的意义。到目前为止，OMFEs的研究中存在的最大问题就是不能有效调控OMFEs，以至于对OMFEs的物理机制还存在较大争议。在本项目中，我们利用新近发现的高场效应作为自旋态演变过程的灵敏“探针”，通过在“e-h 对”复合区附近掺入客体分子、插入隧穿层以及空穴阻挡层等途径，并且借助于光电双激发驱动方式，控制“e-h 对”界面自旋态的形成及演化过程，掌握了调控有机半导体中的奇特磁效应的方法。在此基础上，利用瞬态电致发光技术、速率演变方程和激子湮灭唯象理论揭示了OMFEs的物理起源。本项目所取得的重要结果如下：(i)找到了操控掺杂体系主客体分子间的“e-h 对”的界面自旋态调控OMFEs的方法；(ii)掌握了插入隧穿层和空穴阻挡层改变界面“e-h 对”的自旋态来调控“e-h 对”和传导电荷聚集状态的途径，对OMFEs进行了有效调控；(iii)借助速率演变方程，确认了三重激子对(TTA →S*→S0+hv)的自旋演变过程可以使得量子产率突破25%的理论极限；(iv)利用光电双激发驱动模式，获得了小磁场下正、负偏压的磁电导相反的变化规律，实现了对小磁场范围内的磁电导效应的调控，并结合器件中激子输运规律，证实了双极化子演变过程是小磁场下磁效应的主要原因。在本项目执行过程中，共计发表国外A1类论文21篇，国内T类论文12篇，国内A1类论文1篇，申获批专利1项，成功立项重庆市杰出青年项目、中央高校业务基金重大项目等课题。