Exploring charge generation and separation in tandem organic light-emitting diodes based on magneto-electroluminescence

Abstract

Abstract 5,6,11,12-tetraphenylnaphthacene (rubrene) exhibits resonant energy properties (ES1,rub≈2ET1,rub), resulting in rubrene-based OLED devices that undergo singlet fission (STT) process at room temperature. This unique process gives rise to a distinct magneto-electroluminescence (MEL) profile, differing significantly from the typical intersystem crossing (ISC) process. Therefore, toward investigate charge generation and separation in the interconnector, and the mechanism of charge transport in tandem OLEDs at room temperature using MEL tools. This paper fabricates tandem OLEDs composed of green (Alq3) and yellow (Alq3:rubrene) electroluminescence (EL) units using different interconnector. The results showed that all devices exhibited significant rubrene emission, but MEL didn’t show an STT process with increasing magnetic field, but rather a triplet-triplet annihilation (TTA) process. Because of direct carrier trapping (DCT) in doped EL units, which hinders the transport of rubrene trapped charges, resulting in an extension of the triplet exciton (T1, rub) lifetime. Thus, the increased T1, rub concentration causes TTA occur at room temperature, causing the rapid decrease of MEL in all devices under high magnetic fields. In devices with only TTA process, the TTA increases with the increasing current. Therefore, the high magnetic field of devices A~C is only related to TTA. The high magnetic field TTA of the device D in Alq3/HAT-CN interconnector regardless of current. This is because the two EL units in the device emission together, resulting in the triplet-charge annihilation (TQA) process of Alq3 in the high magnetic field of the MEL. Furthermore, the MEL rapid increase of low magnetic field in all devices is caused by ISC between Alq3 polaron pairs. The throughout process involves the Förster and Dexter energy transfer (i.e. FET and DET). This article not only novel insights into charge generation and separation in the interconnector, enhancing our understanding of the microscopic mechanisms in tandem OLED devices.