掺杂无定形有机半导体的载流子传输与激子动力学研究

发布时间：2019-03-09 14:28

【摘要】：随着有机光电子学的发展,掺杂无定形有机半导体在有机光电器件中得到了广泛应用。目前,对掺杂无定形有机半导体的电荷传输机理和激子动力学的研究还不完善。本论文结合理论计算和实验,系统研究了掺杂对无定形有机半导体的电荷传输的影响;基于激子动力学,系统研究了热活化敏化发光器件的效率滚降和器件寿命。主要成果为:1.通过实验和蒙特卡洛模拟(MC),系统地研究了陷阱对无定形有机半导体迁移率的影响,提出竞争性跳跃传输模型合理地解释了无定形有机半导体的陷阱效应。实验和MC模拟均表明,对浅陷阱而言,迁移率随陷阱深度增加而减小;深陷阱的引入对迁移率没有显著的降低作用,但大大降低了器件中的有效传输载流子浓度。浅陷阱显著增大了体系的有效能量无序度,而深陷阱对有效能量无序度的影响较小。基于离传输能级越近的载流子发生到传输能级的跳跃几率越大的思想,本文提出了竞争性跳跃传输模型。模型的结果很好地解释了实验上的迁移率-温度关系、迁移率-载流子浓度关系和迁移率-陷阱深度关系。2.以8-羟基喹啉铝(Alq_3):4,4'-N,N'-二咔唑基联苯(CBP)蒸镀薄膜作为研究对象,系统研究了掺杂无定形有机半导体的迁移率随掺杂浓度的变化规律。Alq_3:CBP掺杂半导体的迁移率随CBP浓度的增加先下降后升高。当CBP掺杂浓度超过10%时,迁移率-掺杂浓度关系与渗流理论实现了很好的拟合。CBP的空穴和电子传输渗流阈值分别为9%和8.3%。利用短程有序假设计算了CBP跳跃传输的配位数,结合键渗流理论,对CBP的渗流阈值实现了准确地预测。3.通过对主客体掺杂型OLED器件的激子动力学进行研究,证明当主体的小单-三线态劈裂(ΔE_(ST))和主客体间的大能量传递速率同时满足时,热活化敏化发光可以同时实现高效率、低效率滚降和长器件寿命。TADF器件的效率滚降的主要原因是单线态-三线态湮灭和三线态-三线态湮灭。导致TADF器件具有高效率滚降的主要原因是:同一分子难以同时具有小ΔE_(ST)和大辐射跃迁速率,从而具有低三线态浓度。热活化敏化发光利用了主客体间快速的能量转移,可以有效降低三线态浓度,从而在高亮度下降低器件的发光效率损失,实现低效率滚降。同时,低三线态浓度降低了主体通过TPA生成缺陷的速率,从而使热活化敏化发光的亮度随时间的衰减变慢,使器件寿命变长。
[Abstract]:With the development of organic optoelectronics, doped amorphous organic semiconductors have been widely used in organic optoelectronic devices. At present, the study of charge transfer mechanism and exciton dynamics of doped amorphous organic semiconductors is not perfect. In this thesis, the effect of doping on charge transfer in amorphous organic semiconductors is systematically studied, and based on exciton dynamics, the efficiency drop and device lifetime of thermally activated sensitized light emitting devices are systematically studied. Key results are: 1. The effects of traps on the mobility of amorphous organic semiconductors are systematically studied by experiments and Monte Carlo simulation (MC),. A competitive jump transport model is proposed to explain the trap effect of amorphous organic semiconductors reasonably. Both experiments and MC simulations show that for shallow traps, mobility decreases with the increase of trap depth, and the introduction of deep traps has no significant effect on mobility reduction, but greatly reduces the effective carrier concentration in the device. Shallow traps significantly increase the effective energy disorder of the system, while deep traps have little effect on the effective energy disorder. In this paper, a competitive jump transfer model is proposed based on the idea that the carrier closer to the transfer energy level is more likely to jump from the carrier to the transfer level. The model results well explain the experimental mobility-temperature relationship, mobility-carrier concentration relationship and mobility-trap depth relationship. 8-hydroxyquinoline aluminum (Alq_3): 4,4-N, N-dicarbazole-based biphenyl (CBP) evaporation film was used as the research object. The variation of mobility of doped amorphous organic semiconductors with doping concentration has been studied systematically. The mobility of ALQ _ 3:CBP doped semiconductors decreases first and then increases with the increase of CBP concentration. When the doping concentration is more than 10%, the mobility-doping concentration relationship is well fitted with the percolation theory. The hole and electron transport thresholds of CBP are 9% and 8.3%, respectively. Based on the assumption of short range order, the coordination number of CBP jump transmission is calculated, and the percolation threshold of CBP is predicted accurately by using bond percolation theory. 3. By studying the exciton dynamics of host-guest doped OLED devices, it is shown that when the small single-triple state splitting (螖 E _ (ST) and the high energy transfer rate between host and guest are satisfied, Thermal activation sensitized luminescence can simultaneously achieve high efficiency, low efficiency roll-off and long device lifetime. The main reasons for the efficiency roll-off of TADF devices are singlet-triplet annihilation and triplet-trilinear annihilation. The main reason for the high efficiency roll-off of TADF device is that it is difficult for the same molecule to have small 螖 E _ (ST) and large radiative transition rate at the same time, so it has a low concentration of triplet state. Thermal activation sensitized luminescence makes use of the fast energy transfer between host and guest, which can effectively reduce the concentration of triplet state, so as to reduce the loss of luminous efficiency of the device at high brightness and realize the low efficiency roll-off. At the same time, the low triplet concentration reduces the rate of defects generated by the main body through TPA, so that the brightness of thermally activated photoluminescence slows down with time, and the lifetime of the device becomes longer.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN30

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