Extremely stable graphene electrodes doped with macromolecular acid

Sung-Joo Kwon,Tae-Woo Lee,Byung Hee Hong,Youngsoo Kim,Yang Yang,Kwang S Kim,Nannan Li,Sunmin Ryu,Dong Jin Kim,Tae-Hee Han,Sang-Hoon Bae,Taeg Yeoung Ko

doi:10.1038/s41467-018-04385-4

Abstract

Although conventional p-type doping using small molecules on graphene decreases its sheet resistance (Rsh), it increases after exposure to ambient conditions, and this problem has been considered as the biggest impediment to practical application of graphene electrodes. Here, we report an extremely stable graphene electrode doped with macromolecular acid (perfluorinated polymeric sulfonic acid (PFSA)) as a p-type dopant. The PFSA doping on graphene provides not only ultra-high ambient stability for a very long time (> 64 days) but also high chemical/thermal stability, which have been unattainable by doping with conventional small-molecules. PFSA doping also greatly increases the surface potential (~0.8 eV) of graphene, and reduces its Rsh by ~56%, which is very important for practical applications. High-efficiency phosphorescent organic light-emitting diodes are fabricated with the PFSA-doped graphene anode (~98.5 cd A−1 without out-coupling structures). This work lays a solid platform for practical application of thermally-/chemically-/air-stable graphene electrodes in various optoelectronic devices.

Highlights

Conventional p-type doping using small molecules on graphene decreases its sheet resistance (Rsh), it increases after exposure to ambient conditions, and this problem has been considered as the biggest impediment to practical application of graphene electrodes
Since the development of chemical vapor deposition (CVD) methods to produce high-quality and large-area graphene[2,3,4,5], much research has been devoted to applying graphene in flexible electronics such as organic lightemitting diodes (OLEDs)[8,9,10,11,12,13,14,15,16], organic solar cells[17,18,19], and organic transistors[20,21,22]
To study PFSA doping characteristics on graphene, we spin-cast a PFSA on high-quality and large-area single-layered graphene (SLG) that had been prepared using CVD on Cu foil, followed by conventional wet-transfer[4,8,10,14]

Summary

Introduction

Conventional p-type doping using small molecules on graphene decreases its sheet resistance (Rsh), it increases after exposure to ambient conditions, and this problem has been considered as the biggest impediment to practical application of graphene electrodes. Seoul National University, 1 Gwanak-ro Gwanak-gu, Seoul 08826, Republic of Korea These authors contributed : Sung-Joo Kwon, Tae-Hee Han. Graphene has outstanding electrical, mechanical, and optical properties[1,2,3,4,5], so it has been regarded as an alternative to indium tin oxide (ITO), which is the conventional transparent electrode in optoelectronic devices but is not suitable for electrodes in flexible optoelectronics due to its brittleness and increasing cost[6,7]. Ideal chemical doping of graphene for practical use as an anode in electronic devices should achieve: (1) low Rsh, (2) high WF, (3) high stability against heat, chemical, and ambient conditions, (4) smooth film surface, and (5) high OT

Methods

Results

Conclusion