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- 저자 : MUDE NAGARJUNA NAIK (검색결과 1 건)
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(A) Study on High Efficiency and Long Lifetime InP-based Quantum Dot Light-Emitting Diodes
MUDE NAGARJUNA NAIK 경희대학교 대학원 2023 국내박사
This study focus on the improvement of high efficiency and long-lifetime InP-based quantum dot light-emitting diodes (QLEDs). Generally, zinc oxide (ZnO) is commonly used as an electron transport layer (ETL) in QLEDs due to its superior properties compared to other metal-oxide ETLs. However, the efficiency and device lifetime of QLEDs shows poor performances due to charge imbalance because of its high mobility and well-matched energy level of ZnO with QD emissive layer (EML). To overcome such issues we have developed different techniques to modulate the charge injection and electronic structure behavior of ZnO. This research work is divided into five different parts and emphasis on improvement of InP-based QLED device performance. In the first part, we studied about the magnesium (Mg) doped ZnO NPs as ETL in inverted QLED and applied self-aging technique. The maximum external quantum efficiency (EQE) of inverted red InP-QLED is improved from 4.4% to 10.2%. This study specifies that a decrease in electron injection is due to raise in conduction band minimum (CBM) after aging times. During the aging periods of QLED device, the oxygen vacancies of ZnMgO NPs is reduced, which causes the conductivity of ZnMgO NPs to decrease. As a result, the exciton quenching is suppressed at the ZnMgO NPs/QD interface and charge balance is enhanced. In second part, we employed optimized sol-gel ZnMgO ETL and a high mobility hole transport layer (HTL) with deep HOMO level in inverted red InP-based QLEDs. To decrease the ZnMgO NPs ETL mobility, a sol−gel ZnMgO ETL with a 17% doping of Mg, at low annealing temperature (180 °C), and self-aging method is used on ITO. Good charge balance condition and suppression of non-radiative losses in QLEDs are achieved by high mobility HTL (DBTA) and an optimized Zn0.83Mg0.17O sol-gel ETL with self-aging technique. The QLED shown a maximum EQE of 21.8% with a half-lifetime (LT50) of 1095 hours at 1000 cd/m2. We also examined, with and without UV-ozone treatment effect on ITO and attained a maximum EQE of 20.2%. In the third part, we studied about the BPPB small molecule doped ZnO as hybrid interlayer in inverted red InP-QLEDs. The ZnO:BPPB (15 wt%) device showed a maximum EQE of 16.7% with a half-lifetime (LT50) of 595 hours. Using a 15 nm hybrid interlayer, the exciton quenching of QD at the interface is suppressed and also reduced the electron injection of ZnO to match the charge balance. In the fourth part, used a novel stable inorganic zinc sulfide (ZnS) ETL material, which has a relatively higher CBM and lower electron mobility compared to ZnO. Analysis shows that by using ZnO/ZnS cascaded ETL, the electron injection is reduced resulting in an improvement of charge balance in the QD layer, and also the exciton quenching is suppressed and preserves the emission properties of QDs. The optimized device with ZnO/ZnS cascaded ETL shows a maximum EQE of 10.8%, maximum current efficiency (CE) of 37.5 cd/A, and a long lifetime (LT50) of 1000 hours at 1000 cd/m2 in inverted green InP-QLED device. We also studied QD:HTL doping approach in inverted red QLED device, achieved a maximum EQE of 11.5% with a long operational lifetime (LT50) of 3800 hours at 1000 cd/m2. In final part, we studied about (nickel) Ni doping in ZnO as an alternative ETLs. Using Ni-doping in ZnO, the CBM and conductivity can be modulated, which helps in enhancement of charge balance in the QLEDs. The optimized devices with NiZnO-3% ETL shows a maximum EQE of 5.0% with a long operational lifetime. Furthermore, using ZnS as interlayer, the device demonstrated a maximum EQE of 10.6 %, which are 2.1-fold higher than NiZnO-3% ETL devices. The device also exhibited a long operational lifetime (LT50) of 2600 hours at 1000 cd/m2.
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