title: Multifunctional Dendrimer Ligands for High-Efficiency, Solution-Processed Quantum Dot Light-Emitting Diodes.
abstract: We present multifunctional dendrimer ligands that serve as the charge injection controlling layer as well as the adhesive layer at the interfaces between quantum dots (QDs) and the electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs). Specifically, we use primary amine-functionalized dendrimer ligands (e.g., a series of poly(amidoamine) dendrimers (PADs, also referred to PAMAM)) that bind to the surface of QDs by replacing the native ligands (oleic acids) and also to the surface of ZnO ETL. PAD ligands control the electron injection rate from ZnO ETL into QDs by altering the electronic energy levels of the surface of ZnO ETL and thereby improve the charge balance within QDs in devices, leading to the enhancement of the device efficiency. As an ultimate achievement, the device efficiency (peak external quantum efficiency) improves by a factor of 3 by replacing the native ligands (3.86%) with PAD ligands (11.36%). In addition, multibranched dendrimer ligands keep the QD emissive layer intact during subsequent solution processing, enabling us to accomplish solution-processed QLEDs. The approach and results in the present study emphasize the importance of controlling the ligands of QDs to enhance QLED performance and also offer simple yet effective chemical mean toward all-solution-processed QLEDs.
authors.affiliation: Department of Chemical and Biological Engineering, Korea University , Seoul 02841, Republic of Korea.
authors.forename: Ikjun
authors.initials: I
authors.lastname: Cho
authors.forename: Heeyoung
authors.initials: H
authors.lastname: Jung
authors.affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 34141, Republic of Korea.
authors.forename: Byeong Guk
authors.identifier: 0000-0002-0544-364X
authors.initials: BG
authors.lastname: Jeong
authors.forename: Jun Hyuk
authors.initials: JH
authors.lastname: Chang
authors.affiliation: Department of Chemical and Biological Engineering, Korea University , Seoul 02841, Republic of Korea.
authors.forename: Younghoon
authors.initials: Y
authors.lastname: Kim
authors.forename: Kookheon
authors.initials: K
authors.lastname: Char
authors.affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 34141, Republic of Korea.
authors.forename: Doh C
authors.identifier: 0000-0002-3489-6189
authors.initials: DC
authors.lastname: Lee
authors.forename: Changhee
authors.initials: C
authors.lastname: Lee
authors.affiliation: Department of Chemical and Biological Engineering, Korea University , Seoul 02841, Republic of Korea.
authors.forename: Jinhan
authors.initials: J
authors.lastname: Cho
authors.affiliation: Photoelectronic Hybrids Research Center, Korea Institute of Science and Technology (KIST) , Seoul 02792, Republic of Korea.
authors.forename: Wan Ki
authors.identifier: 0000-0002-3832-2449
authors.initials: WK
authors.lastname: Bae
keywords: adhesive layer; charge injection; dendrimer ligands; interface engineering; quantum dot-based light-emitting diode