Performance improvement of organic light emitting diode with aluminum oxide buffer layer for anode modification

Abstract

A thin Al 2 O 3 insulating buffer layer deposited on indium tin oxide (ITO) anode by atomic layer deposition has been investigated for organic light-emitting diodes (OLEDs). With an optimal thickness of 1.4 nm and low density of structural defects of the Al 2 O 3 film, the OLEDs current efficiency and power efficiency were simultaneously improved by 12.5% and 23.4%, respectively. The improvements in both current and power efficiency mean lower energy loss during holes injection process and better balanced charge injection. To understand the mechanism behind the enhanced performance of OLED by the buffer layer, a series of Al 2 O 3 films of different thicknesses were deposited on ITO anode and characterized. The roughness, sheet resistance, and surface potential (E F 0 ) of the Al 2 O 3 modified ITO were characterized. Also, the properties of Al 2 O 3 films were investigated at the device level. It is believed that the block of holes injection by the Al 2 O 3 buffer layer makes more balanced carrier density in the emitting layer, thus enhances the current efficiency. Although less number of holes are injected into OLED due to the Al 2 O 3 buffer layer, quantum tunneling through the ultra-thin buffer layer play an important role in contributing to the holes injection, which avoids crossing the interface barrier, resulting in less energy consumed and power efficiency enhanced. V C 2013 AIP Publishing LLC. [http://dx.

Insertion of an Inorganic Barrier Layer as a Method of Improving the Performance of Quantum Dot Light-Emitting Diodes

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“…The efficiency degradation of QLEDs and OLEDs has been shown to originate from metal ion diffusion and migration, unbalanced rate of electron and hole injection, − and Auger recombination . To improve the performance of QLEDs, many researchers have tried to balance the rates of electron and hole injection into the EML by inserting nonconductive materials as a carrier-blocking layer ,, and attempted to enhance charge transfer within the QD layer by shortening the length of QD-bound ligands to increase the QD packing density . In addition, various approaches such as core–shell alloy/gradient shell formation and change of shell thickness have been adopted to reduce the number of defects originating from the lattice mismatch at the core–shell interface in core–shell-structured QDs.…”

Investigation of hole injection enhancement by MoO3 buffer layer in organic light emitting diodes

“…Organic light emitting diodes (OLEDs) have attracted much attention in the past two decades because of their high efficiency, light weight, flexibility, and easy fabrication. [1][2][3][4][5][6][7] Achieving efficient hole injection is a fundamental topic in OLEDs. Indium tin oxide (ITO) is usually used as transparent conductive anode in OLEDs.…”

Observation of Nanometer-Sized Electro-Active Defects in Insulating Layers by Fluorescence Microscopy and Electrochemistry

“…ss elec (1) where n is the number of electrons exchanged, F is Faraday's constant, D is the diffusion coefficient, and C* is the bulk concentration. The value of D for FcDM is taken as 6.7 × 10 −6 cm 2 /s.…”