Search

The storage of charges in organic light-emitting diodes (OLEDs) has drawn much attention for its damage to device performance as well as the loss to carriers. Thus, it is essential to address the issue and do further investigation. The traditional approach to storage analysis is mainly based on transient measurement since it is sensitive to transient instead of steady signal. In this paper, we proposed a new benchmark to investigate the single-layer OLEDs capable of stored charges with poly (methyl methacrylate) (PMMA), which is just based on electrical and optical characteristics. Since the stored charges contribute both to luminance and current of the devices with PMMA, the area between them can be taken as a benchmark and evaluated the storage of charges. In our experiment, the areas of 4 nm, 6 nm, 8 nm, and 10 nm PMMA devices are 0.348, 0.554, 0.808, and 0.894, respectively, indicating a higher capability of storage in thicker PMMA. It is exactly in line with the results taken from transient electroluminescence (EL) measurement. Thus, this new benchmark is practical and provides a more accessible approach to investigate the storage of charges in OLEDs. [ABSTRACT FROM AUTHOR]

In this paper, capacitance/conductance-voltage characteristics (C/G-V) under illumination was achieved to investigate the dynamic mechanism of stored charges in OLEDs with a structure of ITO/ PEDOT:PSS/PMMA/Alq3/Al. For all devices, at least two peaks presented in the optical capacitance-voltage curve. Compared to curves of devices under dark, the first peak increased remarkably with a deviation to Vbi, which can be explained in the form of stored charges combined with the optical conductance characteristics. It was also found that a great decrease in capacitance is followed by the collapse of the first peak with PMMA thickness increased. It can account for the presence of interfacial charges, which is proved further by the conductance curves. To the device with 10 nm PMMA, a third peak took place in optical capacitance and it was due to the storage of electrons by PMMA. Also, the first capacitance peak enhanced approximate linearly as the illumination power increased, which can verify the contribution of the stored charges. Additionally, it shows the potential for the stored charges in optical detections. [ABSTRACT FROM AUTHOR]

Exciplex states play a crucial role in governing the ultimate device performance, as both current density-voltage-luminescence characteristics and external quantum efficiency directly depend on it. For electron-hole evolution, exciplex states represent the intermediate but essential step between exciton recombination and dissociation. Therefore, the fundamental understanding of the processes involving the exciplex state is essential for utilizing such mediate state to achieve high emission efficiencies approaching the theoretical limits with simple structured organic light-emitting diodes (OLEDs). Herein, we systemically investigate the evolution of exciplex states using transient photoluminescence measurements compiling with transient electroluminescence measurements on high-performance exciplex type thermally activated delayed fluorescence (TADF) OLEDs. The dynamic properties of the long-lived fluorescent exciplex states upon both photo-excitation and electro-excitation offer in-depth insight to the fundamental mechanisms driving its decay pathways, and by studying the electric-field dependent motion of exciplex, we can explore its transport and emission evolution. [ABSTRACT FROM AUTHOR]