Functional Pyrene-Pyridine-Integrated Hole-Transporting Materials for Solution-Processed OLEDs with Reduced Efficiency Roll-Off

Krishan Kumar; Kiran Kishore Kesavan; Diksha Thakur; Subrata Banik; Jayachandran Jayakumar; Chien-Hong Cheng; Jwo-Huei Jou; Subrata Ghosh

doi:10.1021/acsomega.0c04080

Functional Pyrene-Pyridine-Integrated Hole-Transporting Materials for Solution-Processed OLEDs with Reduced Efficiency Roll-Off

ACS Omega. 2021 Apr 15;6(16):10515-10526. doi: 10.1021/acsomega.0c04080. eCollection 2021 Apr 27.

Authors

Krishan Kumar¹, Kiran Kishore Kesavan², Diksha Thakur¹, Subrata Banik³, Jayachandran Jayakumar⁴, Chien-Hong Cheng⁴, Jwo-Huei Jou², Subrata Ghosh¹

Affiliations

¹ School of Basic Sciences, IIT Mandi, Mandi, Himachal Pradesh 175005, India.
² Department of Materials Science and Engineering, National Tsing Hua University, 101, Sec. 2, Guang-Fu Road, Hsinchu 30013, Taiwan, R.O.C.
³ Department of Chemistry, School of Chemical and Biotechnology, SASTRA Deemed University, Thanjavur 613401, Tamil Nadu, India.
⁴ Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan, R.O.C.

Abstract

A series of new functional pyridine-appended pyrene derivatives, viz., 2,6-diphenyl-4-(pyren-1-yl)pyridine (Py-03), 2,6-bis(4-methoxyphenyl)-4-(pyren-1-yl)pyridine (Py-MeO), 4-(pyren-1-yl)-2,6-di-p-tolylpyridine (Py-Me), and 2,6-bis(4-bromophenyl)-4-(pyren-1-yl)pyridine (Py-Br) were designed, developed, and studied as the hole-transporting materials (HTMs) for organic light-emitting diode (OLED) application. The crystal structures of two molecules revealed to have a large dihedral angle between the pyrene and pyridine units, indicating poor π-electronic communication between them due to ineffective orbital overlap across the pyrene-pyridine systems as the two p-orbitals of pivotal atoms are twisted at 66.80° and 68.75° angles to each other in Py-03 and Py-Me, respectively. The influence of variedly functionalized pyridine units on the electro-optical properties and device performance of the present integrated system for OLED application was investigated. All of the materials have suitable HOMO values (5.6 eV) for hole injection by closely matching the HOMOs of indium tin oxide (ITO) and the light-emitting layer. All of the synthesized molecules have suitable triplet energies, glass transition temperatures, and melting temperatures, which are highly desirable for good HTMs. The pyrene-pyridine-based devices demonstrated stable performance with low-efficiency roll-off. The device with Py-Br as HTM showed a maximum luminance of 17300 cd/m² with a maximum current efficiency of 22.4 cd/A and an EQE of 9% at 3500 cd/m² with 7% roll-off from 1000 to 10 000 cd/m². Also, the devices with Py-Me and Py-03 showed performance roll-up while moving from 1000 to 10 000 cd/m².