Performance Improvement of Organic Light Emitting Diodes Using Poly(N‐vinylcarbazole) (PVK) as a Blocking Layer

Abstract

High efficiency organic light-emitting-devices (OLED) have been fabricated by incorporation of a polymeric layer as a controller of the unbalanced charge. In device configuration of ITO/PEDOT:PSS/PVK/Alq 3 /LiF:Al, poly(N-vinylcarbazole) (PVK) was selected as a blocking layer (BL) because it has a hole transporting property and a higher band gap, especially a lower LUMO level than the emitting layer (Alq 3 ) and a higher HOMO level than the hole injection layer (PEDOT: PSS). As a result, the optimal structure with this bl layer showed a peak efficiency of 6.89 cd/A and 2.30 lm/W compared to the device without the PVK layer of 1.08 cd/A, 0.27 lm/W. This result shows that the PVK layer could effectively block the electrons from metal cathode and confine them in the emitting layer and accomplish the charge balance, which leads to enhanced hole-electron balance for achieving high recombination efficiency.

A New Supramolecular Hole Injection/Transport Material on Conducting Polymer for Application in Light‐Emitting Diodes

“…Excellent hole injection/transport and electron‐blocking properties in combination with good solubility only in polar solvents make the PTC‐U a promising candidate for HITL in the fabrication of high‐efficiency organic or multilayer polymer light‐emitting devices. We achieved a luminous efficiency of 1.5 cd/A and a maximum brightness of 8828 cd/m 2 from the Alq3‐based bilayer device, which is comparable to the reported data (efficiency: 1.70 cd/A or 1.08 cd/A, maximum brightness: 7500 cd/m 2 ) using a conventional PEDOT‐PSS layer as a HITL 20–22. Moreover, a trilayer device using PTC‐U as HITL achieved a maximum brightness levels as high as 48233 cd/m 2 , external quantum efficiency and luminance efficiency of 2.40% and 8.0 cd/A, respectively, which is approximately 1.6 times higher than that of PEDOT‐PSS‐based devices.…”

“…Although the PTC‐U possesses fairly high uracil content, its presence does not interfere the hole‐transporting property of the PTC‐U. It's notable that the performance of the ITO/PTC‐U/Alq3/LiF/Al device in terms of maximum brightness (8828 cd/m2) and luminance efficiency (1.5 cd/A) is higher than multilayer device of ITO/PEDOT‐PSS/Alq3/LiF/Al reported elsewhere,20–22 indicating improved hole injection, transport and electron‐blocking from the U‐U interactions of PTC‐U.…”

Energy transfer from both triplet and singlet energy levels of PVK to DCM2 induced by heavy-ion

“…2. 5 The energy difference between the work function of ITO and the ionization potential of PVK is a bit large (around 1 eV), leading to formation of energy barrier at the interface between ITO and PVK and blocking hole injection. 6 Insertion of PEDOT:PSS would decrease the energy step and play other favorable roles such as smoothing the interface between ITO and PVK.…”

Manufacturing polymer light emitting diode with high luminance efficiency by solution process

“…Therefore, interest of solution processed OLEDs was boosted due to their simple manufacturing process, low cost process and possibility for large area flexible display [1]. This paper presents a solution processed OLEDs who's structures to be ITO/PEDOT:PSS/Ir(mppy) 3 surface morphology [2][3][4]. Hence, we fabricated several OLED devices as a function of emission layer thickness and annealing temperatures in order to find optimized condition for solution processed OLED devices.…”