Enhanced electroluminescence performance of all-inorganic quantum dot light-emitting diodes: A promising candidate for h
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Enhanced electroluminescence performance of allinorganic quantum dot light-emitting diodes: A promising candidate for hole transport layer of Cu-doped NiO nanocrystals Yi-Dong Zhang1,a)
Lei Zhao2
1
Key Laboratory for Micro-Nano Energy Storage and Conversion Materials of Henan Province, Institute of Surface Micro and Nano Materials, Xuchang University, Xuchang 461000, People’s Republic of China 2 School of Electronic and Information Engineering, Lanzhou City University, Lanzhou, Gansu Province 730070, People’s Republic of China a) Address all correspondence to this author. e-mail: [email protected] Received: 25 February 2019; accepted: 25 March 2019
Fabrication and characterization of solution-processed, all-inorganic quantum dots (QDs) light-emitting diodes (QLEDs) incorporating colloidal CdSe/ZnS QDs are presented. Using a simple solvothermal process, Cu-doped NiO nanocrystals were fabricated and applied as a hole transport layer in all inorganic QLEDs. Cu-doped NiO nanocrystals are ascribed to bunsenite cubic structure. The transmittance of the film is more than 81%. The hole-only devices of Au/QDs/Cu–NiO/ITO structures showed that 5% mol Cu doped NiO film obtained the largest hole current. The resulting devices show pure QD electroluminescent emissions with a maximum electroluminescence brightness of 2258 cd/m2 after doping 5% mol Cu in NiO, which is almost 4-fold compared with that of intrinsic NiO due to the enhanced carrier concentration and conductivity. The current efficiency and EQE of the assembled all-inorganic QLED exhibited the maximum values of 1.18 cd/A and 1.223%, respectively.
Introduction Since the Allvisatos group first fabricated light-emitting diodes using cadmium selenide nanocrystals (NCs) and a semiconducting polymer in 1994 [1], quantum dots light-emitting diodes (QLEDs) have achieved great development in the fields of display and illumination in the past 20 years thanks to their excellent advantages compared with organic light-emitting diodes (OLED) such as high color purity, saturated emission, low threshold voltage, and so forth [2, 3]. Traditionally, QLEDs with a sandwich structure is composed of organic carrier transport layers, quantum dots (QDs) emitting layer, and metal or metal oxide electrodes [4, 5]. Usually, owing to the unstable characteristic of organic materials in air, the assembly route of QLEDs not only should be operated in a glove box filled with nitrogen (O2 , 0.1 ppm, H2O , 0.1 ppm) but also need to be encapsulated by an ultraviolet (UV) curing adhesive and sliding glass to cover the assembled QLED device to isolate from the water and oxygen in the air. Therefore, it is still a big challenge to seek proper stable inorganic carrier transport materials to
ª Materials Research Society 2019
replace the organic ones to facilitate the QLEDs assembling process to meet the large-scale commercial applications. In 2008, the Bawendi group first reported all-inorganic QLEDs using NiO and ZnO: SnO2 as the hole transport layer (HTL) and electron transport layer (ETL), respectively, by
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