Performance Improvement of Quantum Dot-Light-Emitting Diodes Enabled by an Alloyed ZnMgO Nanoparticle Electron Transport Layer

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• 作者：Jong-Hoon Kim ; Chang-Yeol Han ; Ki-Heon Lee ; Ki-Seok An ; Wooseok Song ; Jiwan Kim ; Min Suk Oh ; Young Rag Do ; Heesun Yang
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：January 13, 2015
• 年：2015
• 卷：27
• 期：1
• 页码：197-204
• 全文大小：512K
• ISSN：1520-5002

文摘

Since the introduction of inorganic ZnO, typically in the form of nanoparticles (NPs), as an electron transport layer (ETL) material, the device performance of electrically driven colloidal quantum dot-light-emitting diodes (QLEDs), in particular, with either Cd-based II鈥揤I or non-Cd-based III鈥揤 (e.g., InP) quantum dot (QD) visible-emitters, has been rapidly improved. In the present work, three Zn_1鈥?i>xMg_xO (x = 0, 0.05, 0.1) NPs that possess different electronic energy levels are applied as ETLs of solution-processed, multilayered I鈥揑II鈥揤I type QLEDs that consist of a Cu鈥揑n鈥揝, Cu鈥揑n鈥揋a鈥揝, or Zn鈥揅u鈥揑n鈥揝 QD emitting layer (EML) plus a common organic hole transport layer of poly(9-vinlycarbazole). The luminance and efficiency of those QLEDs are found to be strongly dependent on the type of ZnMgO NP ETL, resulting in the substantial improvements by means of alloyed ZnMgO ETL versus pure ZnO one. Ultraviolet photoelectron and absorption spectroscopic measurements on a series of ZnMgO NP films reveal that their conduction band minimum (CBM) levels are systematically closer to the vacuum level with increasing Mg content. Therefore, such beneficial effects of alloyed NPs on QLED performance are primarily ascribed to the reduced electron injection barrier between ETL and QD EML that is enabled by the upshift of their CBM levels.