Journal
OPTICS LETTERS
Volume 46, Issue 6, Pages 1434-1437Publisher
OPTICAL SOC AMER
DOI: 10.1364/OL.414574
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Funding
- National Research Foundation of Korea [2012M3A6A7054855]
- National Research Foundation of Korea [2012M3A6A7054855] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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The surface hydrophilicity of the quantum dot emitting layer was modified via a ligand exchange to prevent damage during hole transport layer deposition in all-solution-processed inverted QLEDs. By using a hydrophilic ligand, the device's current efficiency and external quantum efficiency were significantly improved, providing a new approach for high-efficiency all-solution-processed inverted QLEDs.
In this Letter, the surface hydrophilicity of the quantum dot (QD) emitting layer (EML) was modified via a ligand exchange to prevent QD EML damage upon hole transport layer (HTL) deposition for all-solution-processed inverted QD-light-emitting diodes (QLEDs). The conventional hydrophobic oleic acid ligand (OA-QDs) was partially replaced with a hydrophilic 6-mercaptohexanol (OH-QDs) through a one-pot ligand exchange. Owing to this replacement, the contact angle of a water droplet on the OH-QD films was reduced to 71.7 degrees from 89.5 degrees on the OA-QD films, indicating the conversion to hydrophilic hydroxyl ligands. The OH-QD EML maintained its integrity without any noticeable damage, even after HTL deposition, enabling all-solution processing for inverted QLEDs with well-organized multilayers. Inverted QLEDs with the OH-QD EMLs were compared with those with OA-QD EMLs; the maximum current efficiency of the device with the OH-QD EML significantly improved to 39.0 cd A(-1) from 5.3 cd A(-1), and the peak external quantum efficiency improved to 9.3% from 1.2%, which is a seven-fold increase over the OA-QD device. This approach is believed to be effective for forming solid QD films with resistance to chlorobenzene, a representative HTL solvent, and consequently contributes to high-efficiency all-solution-processed inverted QLEDs. (C) 2021 Optical Society of America
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