Rubrene分子间距对有机发光二极管中单重态激子裂变过程的调控

利用5，6，11，12-tetraphenylnaphthacene（Rubrene）中单重态激子分裂的性质（一个单重态激子（S）可以分裂成两个三重态激子（T），S→T＋T），本文制备了Rubrene与Bathocuproine（BCP）共混型有机发光二极管（OLEDs），测量了器件电致发光的磁效应（Magneto-Electroluminescence，MEL）及其瞬态电致发光光谱．实验发现，随着Rubrene分子间距的增大（掺杂浓度减小），单重态激子分裂强度逐渐变弱，即Rubrene分子间距对内部激子分裂有调控作用．该调控作用表现在两个方面：第一，MEL的高场上升幅度（-500mT处对应的值）随着掺杂浓度减小而下降，当浓度为20wt％时高场出现下降；第二，在～20mT处MEL的值随着掺杂浓度的减小从负变到正．此外，器件瞬态电致发光光谱在撤去脉冲电压后的快速下降部分在小掺杂浓度时下降变快．通过分析单重态激子分裂与Rubrene分子间距之间的关系，以及磁场对单重态激子分裂的影响，我们对该现象做了定性的讨论．

Control of singlet fission processes through modifying the molecular space of Rubrene in OLEDs

By utilizing singlet fission property of 5, 6, 11, 12-tetraphenylnaphthacene （Rubrene）, i.e., a singlet exciton can convert into two triplet excitons （STT）, the Rubrene doped organic light emitting diodes （OLEDs） were fabricated in this work. The magneto-electroluminescence （MEL） and transient electroluminescent were measured in our devices. We found that the strength of singlet fission decreased with decreasing Rubrene concentration （increasing molecular space of Rubrene）, i.e. singlet fission can be regulated through modifying the molecular space in Rubrene. This was manifested in two aspects： first, the magnitude of MEL in higher fields （-500 mT） decreased with decreasing Rubrene concentration. When the doping concentration was 20wt%, the MEL curves in higher fields showed a decline; second, the values of the MEL at B=20 mT change from negative to positive with decreasing Rubrene concentration. In addition, the fast decay component of transient electroluminescence after turning off the voltage pulse had a more rapid decline in lower doped concentration. A qualitative discussion was made by analyzing the relation between singlet fission and molecular space of Rubrene, and exploiting magnetic field dependence of singlet fission.