Efficient Cadmium-Free Inverted Red Quantum Dot Light-Emitting Diodes

Abstract

Here, we report an efficient inverted red indium phosphide (InP) comprising QD (InP/ZnSe/ZnS, core/shell structure) light-emitting diode (QLED) by modulating an interfacial contact between the electron transport layer and emissive InP-QDs and applying self-aging approach. The red InP-QLED with optimized interfacial contact exhibits a significant improvement in maximum external quantum efficiency and current efficiency from 4.42 to 10.2% and 4.70 to 10.8 cd/A, respectively, after 69 days of self-aging, which is an almost 2.3-fold improvement compared to the fresh device. The analysis indicates the consecutive reduction in electron injection and accumulation in the emissive QD due to changes in the conduction band minimum of ZnMgO (0.1 eV after 10 days of storage) through a downward vacuum-level shift according to the aging times. During the device aging periods, the oxygen vacancy of ZnMgO reduces, which leads to lower the conductivity of ZnMgO. As a result, charge balance of the device is improved with the suppression of exciton quenching at the interface of ZnMgO and InP-QD.

51‐2: High Efficiency and Long Lifetime InP‐based Red Quantum Dot Light‐Emitting Diodes

“…To confirm the influence of sol-gel ZnMgO on the performance of EL devices, inverted red InP-QLEDs were fabricated using sol-gel ZnMgO and usually used stacked HTLs [6][7][8] (TCTA/TAPC/HATCN) for electron and hole injection/transport, respectively. The schematic of the fabricated device structure is shown in Figure 2.…”

“…Recently, most of the inverted QLEDs were reported with the thermally evaporated stacked hole injection/transport layers, mainly TCTA/TAPC or NPB/HATCN for efficient hole injection and transport. 5,6 However, these HTL materials are less efficient in terms of mobility and stability. Therefore, to further improve charge balance in the emissive layer and to have long operational lifetime, TCTA and TAPC were replaced with new HTLs consisting of deep HOMO and high mobility (KHU-HTL1 and KHU-HTL2) in our optimized QLED.…”

“…In particular, inverted QLEDs are fabricated by sandwiching an emissive QD layer between solution-processed inorganic electron transport layer (ETL), especially zinc oxide nanoparticles (ZnO NPs) (due to high conductivity, suitable energy level, and easy film formation process) and organic holetransport and injection layers (HTL and HIL). 6 In inverted structure, electrons and holes are injected from the ITO cathode and metal (Al) anode, respectively. Additionally, the inverted structure offers the flexibility of choosing suitable smallmolecule HTL and high temperature processed ETL among several materials.…”

Effect of Air Exposure of ZnMgO Nanoparticle Electron Transport Layer on Efficiency of Quantum-Dot Light-Emitting Diodes

“… 9 − 11 Some authors have pointed to spontaneous interfacial reaction of ZnMgO with Al as a major cause of the aging process, 12 while others proposed vacancy reduction in ZnMgO as a possible reason. 13 Recently, a more sophisticated phenomenon such as resistive switching, i.e., electric-field-induced oxygen vacancies migration, which is an intrinsic property of ZnMgO, has been investigated as potentially detrimental to operational stability. 14 …”

Effects of ZnMgO Electron Transport Layer on the Performance of InP-Based Inverted Quantum Dot Light-Emitting Diodes

“…Developing eco-friendly, low-toxic or non-toxic QD materials is key to solving the above problems [ 14 ]. Indium phosphide (InP)-based QDs have attracted wide attention from researchers because of their high fluorescence quantum yield, low toxicity, and environment friendliness [ 15 , 16 , 17 ], and are considered a candidate to replace Cd-based QDs [ 18 ].…”