High-Performance Flexible Organic Light-Emitting Diodes Using Amorphous Indium Zinc Oxide Anode

Abstract

We demonstrate a high-performance flexible organic light-emitting diode ͑OLED͒ employing amorphous indium zinc oxide ͑IZO͒ anode. The amorphous IZO on flexible polycarbonate ͑PC͒ substrate shows similar electrical conductivity and optical transmittance with commercial ͑ITO͒ glass, even though it was prepared at Ͻ50°C. Moreover, it exhibits little resistance change during 5000 bending cycles, demonstrating good mechanical robustness. A green phosphorescent OLED fabricated on amorphous IZO on flexible PC shows maximum external quantum efficiency of ext = 13.7% and power efficiency of p = 32.7 lm/W, which are higher than a device fabricated on a commercial ITO on glass ͑ ext = 12.4% and p = 30.1 lm/W͒ and ITO on flexible PC ͑ ext = 8.5% and p =14.1 lm/W͒. The mechanical robustness and low-temperature deposition of IZO combined with high OLED performance clearly manifest that the amorphous IZO is a promising anode material for flexible displays. There has been increasing activity for flexible organic lightemitting diodes ͑OLEDs͒ over the past few years, and it has focused on developing indium tin oxide ͑ITO͒-coated polymer substrates, such as polyethylene terephthalate ͑PET͒, 1-5 polycarbonate ͑PC͒,polyimide, 8 polyethersulfone ͑PES͒, 9 polyethylene naphthalate ͑PEN͒, 9 and polycyclic olefin ͑PCO͒. 9 However, ITO electrode comes with its own set of problems such as chemical instability in a reduced ambient, poor transparency in the blue region, release of oxygen and indium into the organic layer, imperfect work function alignment with typical hole-transport layers, and easy deterioration of ITO targets. 5 In addition, the optimum properties of ITO film can only be obtained from fully crystallized film deposited at high temperature ͑ϳ300°C͒ or annealed in air or oxygen ambient. 10 With the increasing interest in the development of flexible OLEDs, there is great need for a more mechanically robust and transparent electrode because the resistance of crystallized ITO films on flexible substrate increases with increasing mechanical stain. The increase in resistance is related to the number of cracks generated in the electrode, which depends on applied strain and film thickness. 1,3 For this reason, new transparent conducting materials have been explored to replace ITO for flexible OLED anodes. To achieve better performance of flexible OLEDs, Zn-based transparent conducting oxide ͑TCO͒ films, such as ZnSn 2 O 4 , ZnSnO 3 , Zn 2 In 2 O 5 , and Al͑Ga͒-doped ZnO, have been applied as the anode.11-16 Among various Zn-based transparent conducting oxides, the Zn-doped In 2 O 3 ͑IZO͒ films recently have been recognized as promising TCO materials for OLEDs due to its good conductivity, high transparency, excellent surface smoothness, high etching rate, and low deposition temperature. [13][14][15][16] In particular, it has been confirmed that electrical and optical properties of amorphous IZO ͑a-IZO͒ films can be optimized at Ͻ50°C without a postannealing process. Therefore it is considered that a-IZO anode films can be applied to...

Light-Emitting Devices – Luminescence from Low-Dimensional Nanostructures

“…At the first stages of the fabrication of OLEDs by Philips, the devices consisted of simple structures of poly(dialkoxy-p-phenylenvinylene) (dialkoxy-PPV) that were situated between a metallic electrode and tin-doped indium oxide (ITO) as the transparent conductive layer [8]. Glass is extensively used as a substrate to fabricate this type of LED, while polyethylene terephthalate (PET) can also be used for fabrication of flexible devices [9,10].…”

Carbon Nanotube Transparent Electrodes

“…Amorphous metal oxides, such as In x Zn 1Àx O, appear to meet the requirement of flexibility [98] but these materials still contain costly indium. Satisfactory p-type or hole conducting has not been yet demonstrated in a readily available TCO material [99].…”

Effect of Thickness on Surface Morphology of Silver Nanoparticle Layer During Furnace Sintering

“…Printing offers the potential for low-cost, large-area electronics for displays, sensors, radiofrequency identification, and polymer micro-electromechanical systems. [1][2][3][4][5][6] Crucial components of printed electronics include conductive lines and electrodes using metal nanoparticle inks. Gold nanoparticles have been used for conductive materials due to their high electrical conductivity and thermal stability.…”