Quantum dot light-emitting diodes using a graphene oxide/PEDOT:PSS bilayer as hole injection layer

Abstract

Quantum dot (QD) light-emitting diode (QLED) displays are highly promising optoelectronic devices, but several critical issues remain to be solved. The hole-electron charge balance is particularly important but hole-injection is more difficult than electron-injection in QLEDs; as a result, good hole injection ability is required. Here, we introduce a graphene oxide (GO) layer between the anode electrode and a typical hole injection layer of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) to improve the hole injection ability of a QLED device. The device with the GO/PEDOT:PSS bilayer hole injection layer exhibits a three-fold increase in brightness and external quantum efficiency as well as doubled current efficiency compared to a counterpart device using a single PEDOT:PSS layer. In addition, the turn-on voltage is improved from 8.35 V to 5.35 V. The dramatic improvements in the optoelectronic performance are attributed to the stepwise energy band structure in the hole injection bilayers; the work function of the GO layer is measured to be 4.98 eV, which reduces the interfacial barrier energy between the anode and PEDOT:PSS layer.

Improved Charge Injection and Transport of Light-Emitting Diodes Based on Two-Dimensional Materials

“…2D materials are promising candidates to replace or modify PEDOT:PSS. In QLEDs, 2D materials have been introduced as HTL, HIL and dopant in composite HIL/HTL to enhance the performance of devices [58][59][60][61]. Figure 5 shows some related structures of QLED devices based on 2D materials.…”

“…Song inserted a GO HIL between ITO and PEDOT:PSS to improve the hole injection ability of QLED devices, as shown in Figure 6c [59]. The QLED device with the GO HIL exhibited a maximum luminance of 6741 cd/m 2 , CE of 1.34 cd/A and EQE of 1.61, which are 282%, 60% and 39% higher than those of the control device without GO HIL.…”

Reduced Graphene Oxide as Efficient Hole Injection Layer for Quantum‐Dot Light‐Emitting Diodes

“…PEDOT:PSS, a common hole injection layer (HIL), has a high electrical conductivity, high optical transparency, and smooth morphology, but it is highly acidic, which can cause erosion of the anode (indium‐tin‐oxide: ITO), resulting in reduced lifetime of QLED devices . To overcome this issue, new hole injection materials such as graphene oxide (GO), and transition metal‐oxides have been intensively studied as an alternative HIL replacing PEDOT:PSS. Examples of typical transition metal‐oxides for HIL include vanadium oxide (V 2 O 5 ), nickel oxides (NiOx), molybdenum oxide (MoO 3 ), and tungsten oxide (WO 3 ) …”

“…GO is inexpensive and easy to use in solution processes, however, GO is an insulator, and as such, its hole injection ability decreases dramatically with increasing layer thickness . Recently, our group reported that the use of a GO/PEDOT:PSS hole injection bilayer can significantly improve the hole injection ability in QLED compared to pure GO HIL, in which the GO layer was as thin as possible (≈2 nm) and the surface coverage of GO was not perfect .…”

“…GO is inexpensive and easy to use in solution processes, however, GO is an insulator, and as such, its hole injection ability decreases dramatically with increasing layer thickness . Recently, our group reported that the use of a GO/PEDOT:PSS hole injection bilayer can significantly improve the hole injection ability in QLED compared to pure GO HIL, in which the GO layer was as thin as possible (≈2 nm) and the surface coverage of GO was not perfect . The partial coverage of GO between the ITO anode and PEDOT:PSS may not ensure the necessary blocking to prevent the erosion of the ITO, and therefore, the bilayer GO/PEDOT:PSS may be not a perfect solution to solve the long‐term stability issue posed by the acidic properties of PEDOT:PSS.…”