Researchers fabricate an economical solution-processed OLED device with higher efficiency and lifetime compared to present state-of-the-art

Solution-processed organic light-emitting diodes (OLEDs) are more economical compared to conventional OLEDs. However, their lifetime and efficiency are limited by the difficulty of stacking the composite layers in the OLED, preventing large-scale commercialization of solution-processed OLEDs. To this end, researchers have now developed a novel thermally cross-linkable poly(iminoarylene), a solvent-resistant hole injection layer material with excellent film-forming properties, optimum energy level and high mobility, a major stepping stone toward commercial viability of solution-processed OLEDs.

Infographic title: A novel, low-cost hole injection layer (HIL) material for solution-processed OLEDs

Infographic caption: Researchers have developed thermally cross-linkable novel HIL material with excellent properties for commercially viable solution-processed OLEDs, overcoming the bottleneck of stacking. This cost-effective solution offers increased efficiency and lifetime compared to popular methods currently in use.

Image credit: Do-Hoon Hwang of Pusan National University

License type: Original content

Usage restrictions: Not to be reproduced without permission

Organic light-emitting diode (OLED) displays are widely used in cameras, mobile phones, television sets, and other modern day electronic devices. However, the present technology for fabricating

 OLEDs is cost and labor intensive. In this regard, solution-processed OLEDs offer the promise of an economical, large-scale fabrication technique. However, solution-processed OLEDs have limited efficiency and lifetime owing to the difficulty of stacking the constituent layers such as the anode, cathode, hole injection layer (HIL), hole transport layer (HTL), etc. on top of each other to construct the LED. “Research is being conducted to solve this problem using solvent-resistant materials. Many HTL materials having solvent resistance have been developed, but research on the HIL has not been conducted much,” explains Professor Do-Hoon Hwang from the Department of Chemistry at Pusan National University, Korea, who has been conducting research on organic semiconductor materials and electronic device applications for over two decades.

To this end, Prof. Hwang and his colleagues have synthesized and characterized a novel solvent-resistant HIL material, thermally cross-linkable poly(iminoarylene) poly(FA₉₀-co-BFA₁₀), and fabricated a functional solution-processed red phosphorescent OLED device using the same. In a recent article published in Chemical Engineering Journal, the researchers have detailed this breakthrough development. This paper was made available online on 22 October 2022 and was published in Volume 454, Part 1, Article number 139944 of the journal on 15 February 2023.

This novel HIL material with over 99% solvent resistance, has an optimum energy level that is intermediate between that of the indium tin oxide (ITO) electrode and the HTL. As a result, the researchers achieved photo-crosslinking of (poly-TPD) as HTL on top of crosslinked HIL. Moreover, the researchers demonstrated that the HIL material has high mobility and excellent film-forming properties that are crucial for the commercial viability of solution-processed OLEDs.

Remarkably, the researchers achieved a greater efficiency and lifetime with this novel HIL material, compared to (PEDOT:PSS), the most widely used hole injection layer material, in terms of efficiency and lifetime.” notes Prof. Hwang.

Taken together, this development is a major step forward for the commercialization of efficient solution-processed OLED displays.

Reference

Authors: Seon Lee Kwak ¹, Hea Jung Park ¹, Jae-Ho Jang ¹, Jeong Yong Park ¹, Jong Mok Park ², Jihoon   Lee ³, and Do-Hoon Hwang ¹

Title of original paper:  Synthesis and characterization of thermally cross-linkable poly

(iminoarylene)-based hole injection layer for solution-processed organic light-emitting diodes

Journal:  Chemical Engineering Journal

DOI: 10.1016/j.cej.2022.139944

Affiliations:

¹Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 46241, Republic of Korea

²Research Center for Advanced Specialty Chemicals, Korea Research Institute of Chemical Technology, Ulsan 44412, Republic of Korea

³Department of Polymer Science and Engineering and Department of IT & Energy Convergence (BK21 FOUR), Korea National University of Transportation, Chungju

27469, Republic of Korea  

*Corresponding author’s email: dohoonhwang@pusan.ac.kr

About Pusan National University

Pusan National University, located in Busan, South Korea, was founded in 1946, and is now the no. 1 national university of South Korea in research and educational competency. The multi-campus university also has other smaller campuses in Yangsan, Miryang, and Ami. The university prides itself on the principles of truth, freedom, and service, and has approximately 30,000 students, 1200 professors, and 750 faculty members. The university is composed of 14 colleges (schools) and one independent division, with 103 departments in all.    

Website: https://www.pusan.ac.kr/eng/Main.do

About the authors

Professor Do-Hoon Hwang is a professor in the Department of Chemistry at Pusan National University and has been conducting research on organic semiconductor materials and electronic device applications for more than 25 years. He has authored over 300 papers and holds over 50 patents.

The first author, Seon Lee Kwak, is a Ph. D student in the Department of Chemistry at Pusan National University and is conducting research on the design and synthesis of charge transport materials that can have solvent resistance through crosslinking.

Lab website: http://chemlab.pusan.ac.kr/chemlabpolymer/index.do

ORCID id: 0000-0003-4183-0185