Tuning Hole-Injection in Organic-Light Emitting Diodes with Self-Assembled Monolayers

Despoina Gkeka; Iain Hamilton; Thalis Stavridis; Zhongzhe Liu; Hendrik Faber; Dipti Naphade; Mantas Marčinskas; Tadas Malinauskas; George Harrison; Begimai Adilbekova; Temur Maksudov; Yue Yuan; Dimitrios Kaltsas; Leonidas Tsetseris; Vytautas Getautis; Mario Lanza; Panos Patsalas; Shadi Fatayer; Thomas D Anthopoulos

doi:10.1021/acsami.4c08088

Tuning Hole-Injection in Organic-Light Emitting Diodes with Self-Assembled Monolayers

ACS Appl Mater Interfaces. 2024 Jul 31;16(30):39728-39736. doi: 10.1021/acsami.4c08088. Epub 2024 Jul 18.

Authors

Despoina Gkeka^{1

2}, Iain Hamilton¹, Thalis Stavridis³, Zhongzhe Liu^{1

4}, Hendrik Faber¹, Dipti Naphade¹, Mantas Marčinskas⁵, Tadas Malinauskas⁵, George Harrison¹, Begimai Adilbekova^{1

2}, Temur Maksudov^{1

2}, Yue Yuan², Dimitrios Kaltsas⁶, Leonidas Tsetseris⁶, Vytautas Getautis⁵, Mario Lanza², Panos Patsalas³, Shadi Fatayer^{1

4}, Thomas D Anthopoulos^{1

7}

Affiliations

¹ KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia.
² Materials Science and Engineering Program, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia.
³ Department of Physics, Aristotle University, Thessaloniki GR-54124, Greece.
⁴ Applied Program, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia.
⁵ Department of Organic Chemistry, Kaunas University of Technology, LT-50254 Kaunas, Lithuania.
⁶ School of Applied Mathematical and Physical Sciences, Department of Physics, National Technical University of Athens, Athens 15780, Greece.
⁷ Henry Royce Institute and Photon Science Institute, Department of Electrical and Electronic Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.

PMID: 39024545
DOI: 10.1021/acsami.4c08088

Abstract

Improving hole injection through the surface modification of indium tin oxide (ITO) with self-assembled monolayers (SAMs) is a promising method for modulating the carrier injection in organic light-emitting diodes (OLEDs). However, developing SAMs with the required characteristics remains a daunting challenge. Herein, we functionalize ITO with various phosphonic acid SAMs and evaluate the SAM-modified anodes in terms of their work function (WF), molecular distribution, coverage, and electrical conductivity. We fabricate and characterize green phosphorescent SAM-based OLEDs and compared their performance against devices based on the conventional poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hole-injection layer. We find that the usage of [2-(3,6-diiodo-9H-carbazol-9-yl)ethyl]phosphonic acid (I-2PACz) SAM yields devices with superior performance characteristics, including a maximum luminance of ∼57,300 cd m^-2 and external quantum efficiency of up to ∼17%. This improvement is attributed to synergistic factors, including the deep WF of ITO/I-2PACz (5.47 eV), the formation of larger I-2PACz molecular clusters, and the intrinsic I-2PACz dipole, that collectively enhance hole-injection.

Keywords: hole-injection; interlayers; organic-light emitting diodes; self-assembled monolayers.