利用红荧烯激子能量共振分析三重态激子-电荷作用的磁电导机制  

Analysis of the mechanism for magneto-conductance induced by triplet-charge interaction by energy resonance of excitons in rubrene

作　　者：贾伟尧[1] 刘虹[1] 臧克宽[1] 刘冬玉 汤仙童 袁德[1] 熊祖洪[1] 

机构地区：[1]西南大学物理科学与技术学院,重庆400715

出　　处：《科学通报》2017年第5期385-393,共9页Chinese Science Bulletin

基　　金：国家自然科学基金(11374242);中央高校基本业务费专项(XDJK2015C149)资助

摘　　要：为了研究三重态激子与电荷作用(triplet-charge interaction,TCI)产生磁电导(magneto-conductance,MC)的原因,分别用Al,Li F/Al和Ca等不同功函数的金属作为阴极制作了一系列红荧烯(rubrene)型有机发光器件.在室温下Al电极器件中出现了随磁场增加单调下降的负MC.器件的电流-电压特征曲线表明,Al电极器件中空穴为多余载流子,电子注入困难易形成陷阱电荷.利用rubrene中单重态激子(singlet,S)和三重态激子(triplet,T)的能量共振改变S激子裂变(STT)和T激子聚变(TTA)来调控T激子的比率,并通过更换阴极来改变电子注入势垒高度从而调控电荷(charge,C)的浓度,最终实现对TCI的调控.调控结果表明,Al电极器件中负的MC不应该是T激子与多余空穴通过解离或者散射通道的TCI引起的,而是T与陷阱中的束缚电子通过TCI的去陷阱(T+C_t→S_0+C)通道淬灭导致的.另外,载流子注入较为平衡的Li F/Al和Ca电极器件的MC比Al电极器件的小1个量级,且随磁场的增加先减小后增大,这并非是因为平衡注入器件内的TCI弱,而是由于器件内rubrene功能层中的陷阱容易被电子占满,TCI去陷阱淬灭通道和陷阱捕获淬灭通道对电流的影响变低.因此,载流子陷阱在TCI的磁效应中具有重要地位,使有机功能层中的陷阱尽量多且不易被载流子占满是利用TCI磁效应的重要方向.To analyze the mechanism for magneto-conductance（MC） induced by triplet-charge interaction（TCI）, the rubrene-based organic emitting devices with Al, LiF /Al and Ca acting as metallic cathodes were fabricated, respectively. The MC in Al-cathode device decreases monotonously with increasing external magnetic field, which is obviously different from the one in LiF /Al- or Ca-cathode device. Using the energy resonance of singlet（S） and triplet（T） excitons in rubrene, the singlet fission and triplet fusion was changed to alter the ratio of T. The charge（C） was also changed by metallic cathode modulated electronic injection barrier. Consequently, the TCI was substantially modulated. The results suggested that the negative MC curves were due to the quenching of T exciton by trapped charges via detrapped channel（T＋Ct→S0＋C）, rather than by dissociation or scattering of excessive charges. It was also suggested that the MC of LiF /Al- and Ca-cathode devices with balanced carriers injection is an order of magnitude smaller than the one of Al-cathode device. Additionally, the MC decreases in low-field region（〈100 mT） and then turns to increase with increasing B field. The weak MC in balanced devices is not due to the weakness of TCI, but to the assumption that the existence of detrapping and trapping channels has a weak impact of on electronic current. This is because the traps in active layer of rubrene are fully occupied by minority electrons which are easier injected from cathode. Hence, the carrier traps in quenching way paly a primary role in the MC response of TCI. Our work suggests that producing plenty enough un-occupied carrier traps in organic functional layer is a promising approach to utilize the MC of TCI.

关 键 词：有机电子器件 能量共振 三重态激子 金属电极 载流子陷阱 

分 类 号：TN303[电子电信—物理电子学]